ageing#Measure of age

File:Hydras (8).JPG, a relative of the jellyfish]]

Human beings and members of other species, especially animals, age and die. Fungi, too, can age.{{Cite journal |vauthors=Mortimer RK, Johnston JR |date=June 1959 |title=Life span of individual yeast cells |url=http://www.escholarship.org/uc/item/9j53s5wd |journal=Nature |volume=183 |issue=4677 |pages=1751–2 |bibcode=1959Natur.183.1751M |doi=10.1038/1831751a0 |pmid=13666896 |hdl-access=free |s2cid=4149521 |hdl=2027/mdp.39015078535278}} In contrast, many species can be considered potentially immortal: for example, bacteria fission to produce daughter cells, strawberry plants grow runners to produce clones of themselves, and animals in the genus Hydra have a regenerative ability by which they avoid dying of old age.

Early life forms on Earth, starting at least 3.7 billion years ago,{{Cite journal |vauthors=Nutman AP, Bennett VC, Friend CR, Van Kranendonk MJ, Chivas AR |date=September 2016 |title=Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures |url=http://ro.uow.edu.au/smhpapers/4157 |journal=Nature |type=Submitted manuscript |volume=537 |issue=7621 |pages=535–538 |bibcode=2016Natur.537..535N |doi=10.1038/nature19355 |pmid=27580034 |s2cid=205250494}} were single-celled organisms. Such organisms (Prokaryotes, Protozoans, algae) multiply by fission into daughter cells; thus single celled organisms have been thought to not age and to be potentially immortal under favorable conditions.{{Cite book |title=Evolutionary Biology of Aging |vauthors=Rose MR |publisher=Oxford University Press |year=1991 |location=New York}}{{Cite journal |vauthors=Partridge L, Barton NH |date=March 1993 |title=Optimality, mutation and the evolution of aging |journal=Nature |volume=362 |issue=6418 |pages=305–11 |bibcode=1993Natur.362..305P |doi=10.1038/362305a0 |pmid=8455716 |s2cid=4330925}} However, evidence has been reported that aging leading to death occurs in the single-cell bacterium Escherichia coli, an organism that reproduces by morphologically symmetrical division.{{cite journal |vauthors=Stewart EJ, Madden R, Paul G, Taddei F |title=Aging and death in an organism that reproduces by morphologically symmetric division |journal=PLOS Biol |volume=3 |issue=2 |pages=e45 |date=February 2005 |pmid=15685293 |pmc=546039 |doi=10.1371/journal.pbio.0030045 |doi-access=free |url=}} Evidence of aging has also been reported for the bacterium Caulobacter crescintus.{{cite journal |vauthors=Ackermann M, Stearns SC, Jenal U |title=Senescence in a bacterium with asymmetric division |journal=Science |volume=300 |issue=5627 |pages=1920 |date=June 2003 |pmid=12817142 |doi=10.1126/science.1083532 |url=}} and the single cell yeast Saccharomyces cerevisiae.{{cite journal |vauthors=Sinclair DA |title=Paradigms and pitfalls of yeast longevity research |journal=Mech Ageing Dev |volume=123 |issue=8 |pages=857–67 |date=April 2002 |pmid=12044934 |doi=10.1016/s0047-6374(02)00023-4 |url=}}{{cite journal |vauthors=Jazwinski SM |title=Growing old: metabolic control and yeast aging |journal=Annu Rev Microbiol |volume=56 |issue= |pages=769–92 |date=2002 |pmid=12213938 |doi=10.1146/annurev.micro.56.012302.160830 |url=}}

Ageing and mortality of the individual organism became more evident with the evolution of eukaryotic sexual reproduction,{{Cite journal |vauthors=Williams GC |year=1957 |title=Pleiotropy, Natural Selection, and the Evolution of Senescence |journal=Evolution |volume=11 |issue=4 |pages=398–411 |doi=10.2307/2406060 |jstor=2406060}} which occurred with the emergence of the fungal/animal kingdoms approximately a billion years ago, and the evolution of seed-producing plants 320 million years ago. The sexual organism could henceforth pass on some of its genetic material to produce new individuals and could itself become disposable with respect to the survival of its species. This classic biological idea has however been perturbed recently by the discovery that the bacterium E. coli may split into distinguishable daughter cells, which opens the theoretical possibility of "age classes" among bacteria.

Even within humans and other mortal species, there are cells with the potential for immortality: cancer cells which have lost the ability to die when maintained in a cell culture such as the HeLa cell line,{{Cite journal |vauthors=Pereira-Smith OM, Ning Y |year=1992 |title=Molecular genetic studies of cellular senescence |journal=Experimental Gerontology |volume=27 |issue=5–6 |pages=519–22 |doi=10.1016/0531-5565(92)90006-L |pmid=1426085 |s2cid=27839420}} and specific stem cells such as germ cells (producing ova and spermatozoa).{{Cite journal |vauthors=Forster P, Hohoff C, Dunkelmann B, Schürenkamp M, Pfeiffer H, Neuhuber F, Brinkmann B |date=March 2015 |title=Elevated germline mutation rate in teenage fathers |journal=Proceedings. Biological Sciences |volume=282 |issue=1803 |pages=20142898 |doi=10.1098/rspb.2014.2898 |pmc=4345458 |pmid=25694621}} In artificial cloning, adult cells can be rejuvenated to embryonic status and then used to grow a new tissue or animal without ageing.{{Cite journal |display-authors=6 |vauthors=Wakayama S, Kohda T, Obokata H, Tokoro M, Li C, Terashita Y, Mizutani E, Nguyen VT, Kishigami S, Ishino F, Wakayama T |date=March 2013 |title=Successful serial recloning in the mouse over multiple generations |journal=Cell Stem Cell |volume=12 |issue=3 |pages=293–7 |doi=10.1016/j.stem.2013.01.005 |pmid=23472871 |doi-access=free}} Normal human cells however die after about 50 cell divisions in laboratory culture (the Hayflick Limit, discovered by Leonard Hayflick in 1961).

{{See also|Old age#Signs}}

{{listen|filename=17.4 kHz sine wave.flac|align=right|title=Hearing loss with age (presbycusis)|description= Teenagers begin to lose the ability to hear high-pitched sounds. Beyond the age of 25, many adults cannot hear this 10-second audio clip at a frequency of 17.4 kHz.{{cite web |url=https://www.scientificamerican.com/article/bring-science-home-high-frequency-hearing/ |title=Sonic Science: The High-Frequency Hearing Test |author=Education.com |work=Scientific American |date=23 May 2013 |accessdate=25 May 2017}}|format=Wav}}

File:Senescence.JPG

File: Age dynamics of the body mass.svg

File:Alzheimer's disease brain comparison.jpg]]

A number of characteristic ageing symptoms are experienced by a majority, or by a significant proportion of humans during their lifetimes.

• Teenagers lose the young child's ability to hear high-frequency sounds above 20 kHz.{{Cite journal |vauthors=Rodríguez Valiente A, Trinidad A, García Berrocal JR, Górriz C, Ramírez Camacho R |date=August 2014 |title=Extended high-frequency (9–20 kHz) audiometry reference thresholds in 645 healthy subjects |journal=International Journal of Audiology |volume=53 |issue=8 |pages=531–45 |doi=10.3109/14992027.2014.893375 |pmid=24749665 |s2cid=30960789}}
• Wrinkles develop mainly due to photoageing, particularly affecting sun-exposed areas such as the face.{{Cite journal |vauthors=Thurstan SA, Gibbs NK, Langton AK, Griffiths CE, Watson RE, Sherratt MJ |date=April 2012 |title=Chemical consequences of cutaneous photoageing |journal=Chemistry Central Journal |volume=6 |issue=1 |pages=34 |doi=10.1186/1752-153X-6-34 |pmc=3410765 |pmid=22534143 |doi-access=free }}
• After peaking from the late teens to the late 20s, female fertility declines.{{Cite book |date=25 March 2015 |chapter=Infertility: Overview |chapter-url=https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0076677/ |title=InformedHealth.org |publisher=Institute for Quality and Efficiency in Health Care |location=Cologne |via=NCBI Bookshelf}}
• After age 30, the mass of the human body is decreased until 70 years and then shows damping oscillations.
• People over 35 years of age are at increasing risk for losing strength in the ciliary muscle of the eyes, which leads to difficulty focusing on close objects, or presbyopia.{{Cite web |title=Facts About Presbyopia |url=https://nei.nih.gov/health/errors/presbyopia |access-date=11 September 2016 |publisher=National Eye Institute |archive-date=4 October 2016 |archive-url=https://web.archive.org/web/20161004195255/https://www.nei.nih.gov/health/errors/presbyopia |url-status=dead }}{{Cite journal |vauthors=Weale RA |year=2003 |title=Epidemiology of refractive errors and presbyopia |journal=Survey of Ophthalmology |volume=48 |issue=5 |pages=515–43 |doi=10.1016/S0039-6257(03)00086-9 |pmid=14499819}} Most people experience presbyopia by age 45–50.{{Cite journal |vauthors=Truscott RJ |date=February 2009 |title=Presbyopia. Emerging from a blur towards an understanding of the molecular basis for this most common eye condition |journal=Experimental Eye Research |volume=88 |issue=2 |pages=241–7 |doi=10.1016/j.exer.2008.07.003 |pmid=18675268}} The cause is lens hardening by decreasing levels of alpha-crystallin, a process which may be sped up by higher temperatures.{{Cite journal |vauthors=Pathai S, Shiels PG, Lawn SD, Cook C, Gilbert C |date=March 2013 |title=The eye as a model of ageing in translational research—molecular, epigenetic and clinical aspects |journal=Ageing Research Reviews |volume=12 |issue=2 |pages=490–508 |doi=10.1016/j.arr.2012.11.002 |pmid=23274270 |s2cid=26015190}}
• Around age 55, hair turns grey.{{Cite journal |vauthors=Pandhi D, Khanna D |date=2013 |title=Premature graying of hair |journal=Indian Journal of Dermatology, Venereology and Leprology |volume=79 |issue=5 |pages=641–53 |doi=10.4103/0378-6323.116733 |pmid=23974581 |doi-access=free}} Pattern hair loss by the age of 55 affects about 30–50% of males{{Cite journal |vauthors=Hamilton JB |date=March 1951 |title=Patterned loss of hair in man; types and incidence |journal=Annals of the New York Academy of Sciences |volume=53 |issue=3 |pages=708–28 |bibcode=1951NYASA..53..708H |doi=10.1111/j.1749-6632.1951.tb31971.x |pmid=14819896 |s2cid=32685699}} and a quarter of females.{{Cite journal |vauthors=Vary JC |date=November 2015 |title=Selected Disorders of Skin Appendages--Acne, Alopecia, Hyperhidrosis |journal=The Medical Clinics of North America |volume=99 |issue=6 |pages=1195–211 |doi=10.1016/j.mcna.2015.07.003 |pmid=26476248}}
• Menopause typically occurs between 44 and 58 years of age.{{Cite journal |vauthors=Morabia A, Costanza MC |date=December 1998 |title=International variability in ages at menarche, first livebirth, and menopause. World Health Organization Collaborative Study of Neoplasia and Steroid Contraceptives |journal=American Journal of Epidemiology |volume=148 |issue=12 |pages=1195–205 |doi=10.1093/oxfordjournals.aje.a009609 |pmid=9867266 |doi-access=free}}
• In the 60–64 age cohort, the incidence of osteoarthritis rises to 53%. Only 20%, however, report disabling osteoarthritis at this age.{{Cite journal |vauthors=Thomas E, Peat G, Croft P |date=February 2014 |title=Defining and mapping the person with osteoarthritis for population studies and public health |journal=Rheumatology |volume=53 |issue=2 |pages=338–45 |doi=10.1093/rheumatology/ket346 |pmc=3894672 |pmid=24173433}}
• Almost half of people older than 75 have hearing loss (presbycusis), inhibiting spoken communication.{{Cite web |date=2016-01-26 |title=Hearing Loss and Older Adults |url=https://www.nidcd.nih.gov/health/hearing-loss-older-adults |access-date=11 September 2016 |publisher=National Institute on Deafness and Other Communication Disorders |format=Last Updated 3 June 2016}} Many vertebrates such as fish, birds and amphibians do not develop presbycusis in old age, as they are able to regenerate their cochlear sensory cells; mammals, including humans, have genetically lost this ability.{{Cite journal |vauthors=Rubel EW, Furrer SA, Stone JS |date=March 2013 |title=A brief history of hair cell regeneration research and speculations on the future |journal=Hearing Research |volume=297 |pages=42–51 |doi=10.1016/j.heares.2012.12.014 |pmc=3657556 |pmid=23321648}}
• By age 80, more than half of all Americans either have a cataract or have had cataract surgery.{{Cite web |date=September 2015 |title=Facts About Cataract |url=https://www.nei.nih.gov/health/cataract/cataract_facts |access-date=14 August 2016}}
• Frailty, a syndrome of decreased strength, physical activity, physical performance and energy, affects 25% of those over 85.{{Cite journal |display-authors=6 |vauthors=Fried LP, Tangen CM, Walston J, Newman AB, Hirsch C, Gottdiener J, Seeman T, Tracy R, Kop WJ, Burke G, McBurnie MA |date=March 2001 |title=Frailty in older adults: evidence for a phenotype |journal=The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences |volume=56 |issue=3 |pages=M146-56 |citeseerx=10.1.1.456.139 |doi=10.1093/gerona/56.3.m146 |pmid=11253156}}Percentage derived from Table 2 in Fried et al. 2001 Muscles have a reduced capacity of responding to exercise or injury and loss of muscle mass and strength (sarcopenia) is common.{{Cite journal |vauthors=Ryall JG, Schertzer JD, Lynch GS |date=August 2008 |title=Cellular and molecular mechanisms underlying age-related skeletal muscle wasting and weakness |journal=Biogerontology |volume=9 |issue=4 |pages=213–28 |doi=10.1007/s10522-008-9131-0 |pmid=18299960 |s2cid=8576449}} Maximum oxygen use and maximum heart rate decline.{{Cite journal |vauthors=Betik AC, Hepple RT |date=February 2008 |title=Determinants of VO2 max decline with aging: an integrated perspective |journal=Applied Physiology, Nutrition, and Metabolism |volume=33 |issue=1 |pages=130–40 |doi=10.1139/H07-174 |pmid=18347663 |s2cid=24468921}} Hand strength and mobility decrease.{{Cite journal |vauthors=Ranganathan VK, Siemionow V, Sahgal V, Yue GH |date=November 2001 |title=Effects of aging on hand function |journal=Journal of the American Geriatrics Society |volume=49 |issue=11 |pages=1478–84 |doi=10.1046/j.1532-5415.2001.4911240.x |pmid=11890586 |s2cid=22988219}}
• Atherosclerosis is classified as an ageing disease.{{Cite journal |vauthors=Wang JC, Bennett M |date=July 2012 |title=Aging and atherosclerosis: mechanisms, functional consequences, and potential therapeutics for cellular senescence |journal=Circulation Research |volume=111 |issue=2 |pages=245–59 |doi=10.1161/CIRCRESAHA.111.261388 |pmid=22773427 |doi-access=free}} It leads to cardiovascular disease (for example, stroke and heart attacks),{{Cite journal |vauthors=Herrington W, Lacey B, Sherliker P, Armitage J, Lewington S |date=February 2016 |title=Epidemiology of Atherosclerosis and the Potential to Reduce the Global Burden of Atherothrombotic Disease |journal=Circulation Research |volume=118 |issue=4 |pages=535–46 |doi=10.1161/CIRCRESAHA.115.307611 |pmid=26892956 |doi-access=free}} which, globally, is the most common cause of death.{{Cite web |last= |date=9 December 2020 |title=The top 10 causes of death |url=https://www.who.int/news-room/fact-sheets/detail/the-top-10-causes-of-death |access-date=11 March 2021 |publisher=WHO}} Vessel ageing causes vascular remodelling and loss of arterial elasticity, and as a result, causes the stiffness of the vasculature.
• Evidence suggests that age-related risk of death plateaus after the age of 105.{{Cite web |date=28 June 2018 |title=Does Human Life Span Really Have a Limit? |url=https://www.webmd.com/healthy-aging/news/20180628/does-human-life-span-really-have-a-limit#1 |website=WebMD}} The maximum human lifespan is suggested to be 115 years.{{Cite news |author-link=Carl Zimmer |date=5 October 2016 |title=What's the Longest Humans Can Live? 115 Years, New Study Says |work=The New York Times |url=https://www.nytimes.com/2016/10/06/science/maximum-life-span-study.html |access-date=6 October 2016 |vauthors=Zimmer C}}{{Cite journal |vauthors=Dong X, Milholland B, Vijg J |date=October 2016 |title=Evidence for a limit to human lifespan |journal=Nature |volume=538 |issue=7624 |pages=257–259 |bibcode=2016Natur.538..257D |doi=10.1038/nature19793 |pmid=27706136 |s2cid=3623127|pmc=11673931 }} The oldest reliably recorded human was Jeanne Calment, who died in 1997 at 122.

Dementia becomes more common with age.{{Cite journal |vauthors=Larson EB, Yaffe K, Langa KM |date=December 2013 |title=New insights into the dementia epidemic |journal=The New England Journal of Medicine |volume=369 |issue=24 |pages=2275–7 |doi=10.1056/nejmp1311405 |pmc=4130738 |pmid=24283198}} About 3% of people between the ages of 65 and 74, 19% of those between 75 and 84, and nearly half of those over 85 years old have dementia.{{Cite book |url=https://books.google.com/books?id=I9ltC-ZrNOMC&pg=PA838 |title=Neurological rehabilitation |vauthors=Umphred D |date=2012 |publisher=Elsevier Mosby |isbn=978-0-323-07586-2 |edition=6th |location=St. Louis, MO |page=838}} The spectrum ranges from mild cognitive impairment to the neurodegenerative diseases of Alzheimer's disease, cerebrovascular disease, Parkinson's disease and Lou Gehrig's disease. Furthermore, many types of memory decline with ageing, but not semantic memory or general knowledge such as vocabulary definitions. These typically increase or remain steady until late adulthood {{Cite book |title=Developmental Influences on Adult Intelligence |vauthors=Schaie KW |year=2005 |isbn=978-0-19-515673-7 |doi=10.1093/acprof:oso/9780195156737.001.0001}}{{page needed|date=November 2013}} (see Ageing brain). Intelligence declines with age, though the rate varies depending on the type and may, in fact, remain steady throughout most of the human lifespan, dropping suddenly only as people near the end of their lives. Individual variations in the rate of cognitive decline may therefore be explained in terms of people having different lengths of life.{{Cite book |title=The Psychology of Ageing: An Introduction |vauthors=Stuart-Hamilton I |publisher=Jessica Kingsley Publishers |year=2006 |isbn=978-1-84310-426-1 |location=London}} There are changes to the brain: after 20 years of age, there is a 10% reduction each decade in the total length of the brain's myelinated axons.{{Cite journal |vauthors=Marner L, Nyengaard JR, Tang Y, Pakkenberg B |date=July 2003 |title=Marked loss of myelinated nerve fibers in the human brain with age |journal=The Journal of Comparative Neurology |volume=462 |issue=2 |pages=144–52 |doi=10.1002/cne.10714 |pmid=12794739 |s2cid=35293796}}{{Cite book |title=Brain Aging: Models, Methods, and Mechanisms |vauthors=Peters A |date=1 January 2007 |publisher=CRC Press/Taylor & Francis |isbn=978-0-8493-3818-2 |veditors=Riddle DR |series=Frontiers in Neuroscience |chapter=The Effects of Normal Aging on Nerve Fibers and Neuroglia in the Central Nervous System |pmid=21204349 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK3873/}}

Age can result in visual impairment, whereby non-verbal communication is reduced,{{Cite book |title=Communication disability in aging: from prevention to intervention |vauthors=Worrall L, Hickson LM |date=2003 |publisher=Delmar Learning |veditors=Worrall L, Hickson LM |location=Clifton Park, NY |pages=32–33 |chapter=Theoretical foundations of communication disability in aging}} which can lead to isolation and possible depression. Older adults, however, may not experience depression as much as younger adults, and were paradoxically found to have improved mood, despite declining physical health.{{Cite journal |vauthors=Lys R, Belanger E, Phillips SP |date=April 2019 |title=Improved mood despite worsening physical health in older adults: Findings from the International Mobility in Aging Study (IMIAS) |journal=PLOS ONE |volume=14 |issue=4 |pages=e0214988 |bibcode=2019PLoSO..1414988L |doi=10.1371/journal.pone.0214988 |pmc=6453471 |pmid=30958861 |doi-access=free}} Macular degeneration causes vision loss and increases with age, affecting nearly 12% of those above the age of 80.{{Cite journal |vauthors=Mehta S |date=September 2015 |title=Age-Related Macular Degeneration |journal=Primary Care |volume=42 |issue=3 |pages=377–91 |doi=10.1016/j.pop.2015.05.009 |pmid=26319344}} This degeneration is caused by systemic changes in the circulation of waste products and by the growth of abnormal vessels around the retina.{{Cite book |title=Communication and aging |vauthors=Nussbaum JF, Thompson TL, Robinson JD |date=1989 |publisher=Harper & Row |veditors=Nussbaum JF, Thompson TL, Robinson JD |location=New York |pages=234–53 |chapter=Barriers to conversation}}

Other visual diseases that often appear with age are cataracts and glaucoma. A cataract occurs when the lens of the eye becomes cloudy, making vision blurry; it eventually causes blindness if untreated.{{Cite web |title=Cataracts {{!}} National Eye Institute |url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/cataracts |access-date=2021-07-03 |website=www.nei.nih.gov}} They develop over time and are seen most often with those that are older. Cataracts can be treated through surgery. Glaucoma is another common visual disease that appears in older adults. Glaucoma is caused by damage to the optic nerve, causing vision loss.{{Cite web |title=Glaucoma {{!}} National Eye Institute |url=https://www.nei.nih.gov/learn-about-eye-health/eye-conditions-and-diseases/glaucoma |access-date=2021-07-03 |website=www.nei.nih.gov}} Glaucoma usually develops over time, but there are variations to glaucoma, and some have a sudden onset. There are a few procedures for glaucoma, but there is no cure or fix for the damage, once it has occurred. Prevention is the best measure in the case of glaucoma.

In addition to physical symptoms, aging can also cause a number of mental health issues as older adults deal with challenges such as the death of loved ones, retirement and loss of purpose, as well as their own health issues. Some warning signs are: changes in mood or energy, changes in sleep or eating habits, pain, sadness, unhealthy coping mechanisms such as smoking, suicidal ideations, and others. [https://medlineplus.gov/olderadultmentalhealth.html Older Adult Mental Health] Older adults are more prone to social isolation as well, which can further increase the risk for physical and mental conditions such as anxiety, depression, and cognitive decline. [https://www.nia.nih.gov/news/social-isolation-loneliness-older-people-pose-health-risks Social isolation, loneliness in older people pose health risks]

A distinction can be made between "proximal ageing" (age-based effects that come about because of factors in the recent past) and "distal ageing" (age-based differences that can be traced to a cause in a person's early life, such as childhood poliomyelitis).

Ageing is among the greatest known risk factors for most human diseases. Of the roughly 150,000 people who die each day across the globe, about two-thirds--100,000 per day--die from age-related causes. In industrialized nations, the proportion is higher, reaching 90%.{{Cite journal |vauthors=De Grey AD |year=2007 |title=Life Span Extension Research and Public Debate: Societal Considerations |journal=Studies in Ethics, Law, and Technology |volume=1 |citeseerx=10.1.1.395.745 |doi=10.2202/1941-6008.1011 |s2cid=201101995}}{{Cite journal |vauthors=Lopez AD, Mathers CD, Ezzati M, Jamison DT, Murray CJ |date=May 2006 |title=Global and regional burden of disease and risk factors, 2001: systematic analysis of population health data |journal=Lancet |volume=367 |issue=9524 |pages=1747–57 |doi=10.1016/S0140-6736(06)68770-9 |pmid=16731270 |s2cid=22609505}}[https://stanford.edu/group/brunet/background.html Brunet Lab: Molecular Mechanisms of Longevity and Age Related Diseases]. Stanford.edu. Retrieved on 11 April 2012.

{{Main|Senescence}}

File:Old woman with young baby boy.JPG

In the 21st century, researchers are only beginning to investigate the biological basis of ageing even in relatively simple and short-lived organisms, such as yeast.{{Cite journal |display-authors=3 |vauthors=Janssens GE, Meinema AC, González J, Wolters JC, Schmidt A, Guryev V, Bischoff R, Wit EC, Veenhoff LM, Heinemann M |date=December 2015 |title=Protein biogenesis machinery is a driver of replicative aging in yeast |journal=eLife |volume=4 |pages=e08527 |doi=10.7554/eLife.08527 |pmc=4718733 |pmid=26422514 |doi-access=free }} Little is known of mammalian ageing, in part due to the much longer lives of even small mammals, such as the mouse (around 3 years). A model organism for the study of ageing is the nematode C. elegans {{ndash}} having a short lifespan of 2–3 weeks {{ndash}} enabling genetic manipulations or suppression of gene activity with RNA interference, and other factors.{{Cite book |title=Caenorhabditis Elegans: Cell Biology and Physiology |vauthors=Wilkinson DS, Taylor RC, Dillin A |publisher=Academic Press |year=2012 |isbn=978-0-12-394620-1 |veditors=Rothman JH, Singson A |pages=353–381 |chapter=Analysis of Aging |chapter-url=https://books.google.com/books?id=F-jp8kwcHiAC}} Most known mutations and RNA interference targets that extend lifespan were first discovered in C. elegans.{{Cite journal |vauthors=Shmookler Reis RJ, Bharill P, Tazearslan C, Ayyadevara S |date=October 2009 |title=Extreme-longevity mutations orchestrate silencing of multiple signaling pathways |journal=Biochimica et Biophysica Acta (BBA) - General Subjects |volume=1790 |issue=10 |pages=1075–1083 |doi=10.1016/j.bbagen.2009.05.011 |pmc=2885961 |pmid=19465083}}

The factors proposed to influence biological ageing fall into two main categories, programmed and error-related.{{Cite journal |vauthors=Jin K |date=October 2010 |title=Modern Biological Theories of Aging |journal=Aging and Disease |volume=1 |issue=2 |pages=72–74 |pmc=2995895 |pmid=21132086}} Programmed factors follow a biological timetable that might be a continuation of inherent mechanisms that regulate childhood growth and development. This regulation would depend on changes in gene expression that affect the systems responsible for maintenance, repair and defense responses.

Factors causing errors or damage include internal and environmental events that induce cumulative deterioration in one or more organs.

{{Main|Hallmarks of aging}}

One 2013 review assessed ageing through the lens of the damage theory, proposing nine metabolic "hallmarks" of ageing in various organisms but especially mammals:{{Cite journal |vauthors=López-Otín C, Blasco MA, Partridge L, Serrano M, Kroemer G |date=June 2013 |title=The hallmarks of aging |journal=Cell |volume=153 |issue=6 |pages=1194–217 |doi=10.1016/j.cell.2013.05.039 |pmc=3836174 |pmid=23746838}}

• genomic instability (mutations accumulated in nuclear DNA, in mtDNA, and in the nuclear lamina)
• telomere attrition (the authors note that artificial telomerase confers non-cancerous immortality to otherwise mortal cells)
• epigenetic alterations (including DNA methylation patterns, post-translational modification of histones, and chromatin remodelling). Ageing and disease are related to a misregulation of gene expression through impaired methylation patterns, from hypomethylation to hypermethylation. {{Cite journal |vauthors=Arleo A, Bares M, Bernard JA, Bogoian HR, Bruchhage MM |date=July 2013 |title=Consensus Paper: Cerebellum and Ageing |journal=Cerebellum |volume=23 |issue=2 |pages=802–832 |doi=10.1007/s12311-023-01577-7 |pmid=37428408|s2cid=259499418 |pmc=10776824 }}
• loss of proteostasis (protein folding and proteolysis)
• deregulated nutrient sensing (relating to the Growth hormone/Insulin-like growth factor 1 signalling pathway{{Broken anchor|date=2024-06-16|bot=User:Cewbot/log/20201008/configuration|target_link=Insulin-like growth factor 1#Aging|reason= The anchor (Aging) has been deleted.}}, which is the most conserved ageing-controlling pathway in evolution and among its targets are the FOXO3/Sirtuin transcription factors and the mTOR complexes, probably responsive to caloric restriction)
• mitochondrial dysfunction (the authors point out however that a causal link between ageing and increased mitochondrial production of reactive oxygen species is no longer supported by recent research)
• cellular senescence (accumulation of no longer dividing cells in certain tissues, a process induced especially by p16INK4a/Rb and p19ARF/p53 to stop cancerous cells from proliferating)
• stem cell exhaustion (in the authors' view caused by damage factors such as those listed above)
• altered intercellular communication (encompassing especially inflammation but possibly also other intercellular interactions)
• inflammageing, a chronic inflammatory phenotype in the elderly in the absence of viral infection, due to over-activation and a decrease in the precision of the innate immune system
• dysbiosis of gut microbiome (e.g., loss of microbial diversity, expansion of enteropathogens, and altered vitamin B12 biosynthesis) is correlated with biological age rather than chronological age.{{Cite journal |vauthors=Ratiner K, Abdeen SK, Goldenberg K, Elinav E |date=March 2022 |title=Utilization of Host and Microbiome Features in Determination of Biological Aging |journal=Microorganisms |volume=10 |issue=3 |page=668 |doi=10.3390/microorganisms10030668 |pmc=8950177 |pmid=35336242 |doi-access=free}}

There are three main metabolic pathways which can influence the rate of ageing, discussed below:

• the FOXO3/Sirtuin pathway, probably responsive to caloric restriction
• the Growth hormone/Insulin-like growth factor 1 signalling pathway{{Broken anchor|date=2024-06-16|bot=User:Cewbot/log/20201008/configuration|target_link=Insulin-like growth factor 1#Aging|reason= The anchor (Aging) has been deleted.}}
• the activity levels of the electron transport chain in mitochondria{{Cite journal |vauthors=Berdyshev GD, Korotaev GK, Boiarskikh GV, Vaniushin BF |year=2008 |title=Molecular Biology of Aging |journal=Cell |publisher=Cold Spring Harbor |volume=96 |issue=2 |pages=347–62 |doi=10.1016/s0092-8674(00)80567-x |isbn=978-0-87969-824-9 |pmid=9988222 |doi-access=free |s2cid=17724023}} and (in plants) in chloroplasts.

It is likely that most of these pathways affect ageing separately, because targeting them simultaneously leads to additive increases in lifespan.{{Cite journal |vauthors=Taylor RC, Dillin A |date=May 2011 |title=Aging as an event of proteostasis collapse |journal=Cold Spring Harbor Perspectives in Biology |volume=3 |issue=5 |pages=a004440 |doi=10.1101/cshperspect.a004440 |pmc=3101847 |pmid=21441594}}

The rate of ageing varies substantially across different species, and this, to a large extent, is genetically based. For example, numerous perennial plants ranging from strawberries and potatoes to willow trees typically produce clones of themselves by vegetative reproduction and are thus potentially immortal, while annual plants such as wheat and watermelons die each year and reproduce by sexual reproduction. In 2008 it was discovered that inactivation of only two genes in the annual plant Arabidopsis thaliana leads to its conversion into a potentially immortal perennial plant.{{Cite journal |vauthors=Melzer S, Lens F, Gennen J, Vanneste S, Rohde A, Beeckman T |date=December 2008 |title=Flowering-time genes modulate meristem determinacy and growth form in Arabidopsis thaliana |url=http://www.repository.naturalis.nl/record/429531 |journal=Nature Genetics |volume=40 |issue=12 |pages=1489–92 |doi=10.1038/ng.253 |pmid=18997783 |s2cid=13225884}} The oldest animals known so far are 15,000-year-old Antarctic sponges,{{Cite news |date=12 June 2017 |title=The oldest living thing on Earth |work=BBC News |url=https://www.bbc.com/news/science-environment-40224991 |access-date=16 September 2017 |vauthors=Chesterton M}} which can reproduce both sexually and clonally.

Clonal immortality apart, there are certain species whose individual lifespans stand out among Earth's life-forms, including the bristlecone pine at 5062 years{{Cite web |title=Oldlist |url=http://www.rmtrr.org/oldlist.htm |access-date=2016-08-12 |publisher=Rocky Mountain Tree Ring Research}} or 5067 years, invertebrates like the hard clam (known as quahog in New England) at 508 years,{{Cite journal |vauthors=Sosnowska D, Richardson C, Sonntag WE, Csiszar A, Ungvari Z, Ridgway I |date=December 2014 |title=A heart that beats for 500 years: age-related changes in cardiac proteasome activity, oxidative protein damage and expression of heat shock proteins, inflammatory factors, and mitochondrial complexes in Arctica islandica, the longest-living noncolonial animal |journal=The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences |volume=69 |issue=12 |pages=1448–61 |doi=10.1093/gerona/glt201 |pmc=4271020 |pmid=24347613}} the Greenland shark at 400 years,{{Cite journal |display-authors=6 |vauthors=Nielsen J, Hedeholm RB, Heinemeier J, Bushnell PG, Christiansen JS, Olsen J, Ramsey CB, Brill RW, Simon M, Steffensen KF, Steffensen JF |date=August 2016 |title=Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus) |url=https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-9911bdd03b09 |journal=Science |volume=353 |issue=6300 |pages=702–4 |bibcode=2016Sci...353..702N |doi=10.1126/science.aaf1703 |pmid=27516602 |hdl-access=free |s2cid=206647043 |hdl=2022/26597}} various deep-sea tube worms at over 300 years,{{Cite journal |vauthors=Durkin A, Fisher CR, Cordes EE |date=August 2017 |title=Extreme longevity in a deep-sea vestimentiferan tubeworm and its implications for the evolution of life history strategies |journal=Die Naturwissenschaften |volume=104 |issue=7–8 |pages=63 |bibcode=2017SciNa.104...63D |doi=10.1007/s00114-017-1479-z |pmid=28689349 |s2cid=11287549}} fish like the sturgeon and the rockfish, and the sea anemoneTimiras, Paola S. (2003) Physiological Basis of Ageing and Geriatrics. Informa Health Care. {{ISBN|0-8493-0948-4}}. p. 26. and lobster.{{Cite web |date=2007-07-05 |title=Is there a 400 pound lobster out there? |url=http://animals.howstuffworks.com/marine-life/400-pound-lobster.htm/printable |publisher=howstuffworks |vauthors=Silverman J}}{{Cite book |title=Consider the Lobster and Other Essays |title-link=Consider the Lobster |vauthors=Wallace DF |publisher=Little, Brown & Company |year=2005 |isbn=978-0-316-15611-0}}{{page needed|date=November 2013}} Such organisms are sometimes said to exhibit negligible senescence.{{Cite journal |vauthors=Guerin JC |date=June 2004 |title=Emerging area of aging research: long-lived animals with "negligible senescence" |journal=Annals of the New York Academy of Sciences |volume=1019 |issue=1 |pages=518–20 |bibcode=2004NYASA1019..518G |doi=10.1196/annals.1297.096 |pmid=15247078 |s2cid=6418634}} The genetic aspect has also been demonstrated in studies of human centenarians.

{{Main|Evolution of ageing}}

Life span, like other phenotypes, is selected for in evolution. Traits that benefit early survival and reproduction will be selected for even if they contribute to an earlier death. Such a genetic effect is called the antagonistic pleiotropy effect when referring to a gene (pleiotropy signifying the gene has a double function – enabling reproduction at a young age but costing the organism life expectancy in old age) and is called the disposable soma effect when referring to an entire genetic programme (the organism diverting limited resources from maintenance to reproduction). The biological mechanisms which regulate lifespan probably evolved with the first multicellular organisms more than a billion years ago. However, even single-celled organisms such as yeast have been used as models in ageing, hence ageing has its biological roots much earlier than multi-cellularity.{{Cite book |last1=Sampaio-Marques |first1=Belém |last2=Burhans |first2=William C. |last3=Ludovico |first3=Paula |title=Yeasts in Biotechnology and Human Health |chapter=Yeast at the Forefront of Research on Ageing and Age-Related Diseases |series=Progress in Molecular and Subcellular Biology |date=2019 |volume=58 |pages=217–242 |doi=10.1007/978-3-030-13035-0_9 |isbn=978-3-030-13034-3 |issn=0079-6484 |pmid=30911895 |hdl=1822/62308 |s2cid=85516879|hdl-access=free }}

• DNA damage theory of ageing: DNA damage is thought to be the common basis of both cancer and ageing, and it has been argued that intrinsic causes of DNA damage are the most important causes of ageing.{{Cite journal |vauthors=Gensler HL, Bernstein H |date=September 1981 |title=DNA damage as the primary cause of aging |journal=The Quarterly Review of Biology |volume=56 |issue=3 |pages=279–303 |doi=10.1086/412317 |jstor=2826464 |pmid=7031747 |s2cid=20822805}}{{Cite journal |vauthors=Freitas AA, de Magalhães JP |year=2011 |title=A review and appraisal of the DNA damage theory of ageing |journal=Mutation Research |volume=728 |issue=1–2 |pages=12–22 |doi=10.1016/j.mrrev.2011.05.001 |pmid=21600302|bibcode=2011MRRMR.728...12F }} Genetic damage (aberrant structural alterations of the DNA), mutations (changes in the DNA sequence), and epimutations (methylation of gene promoter regions or alterations of the DNA scaffolding which regulate gene expression), can cause abnormal gene expression. DNA damage causes the cells to stop dividing or induces apoptosis, often affecting stem cell pools and therefore hindering regeneration. However, lifelong studies of mice suggest that most mutations happen during embryonic and childhood development, when cells divide often, as each cell division is a chance for errors in DNA replication.{{Cite journal |vauthors=Robert L, Labat-Robert J, Robert AM |date=August 2010 |title=Genetic, epigenetic and posttranslational mechanisms of aging |journal=Biogerontology |volume=11 |issue=4 |pages=387–99 |doi=10.1007/s10522-010-9262-y |pmid=20157779 |s2cid=21455794}} A meta analysis study of 36 studies with 4,676 participants showed an association between age and DNA damage in humans.{{cite journal |vauthors=Soares JP, Cortinhas A, Bento T, Leitão JC, Collins AR, Gaivão I, Mota MP |title=Aging and DNA damage in humans: a meta-analysis study |journal=Aging (Albany NY) |volume=6 |issue=6 |pages=432–9 |date=June 2014 |pmid=25140379 |doi=10.18632/aging.100667 |pmc=4100806 |url=}} In the human hematopoietic stem cell compartment DNA damage accumulates with age.{{cite journal |vauthors=Beerman I |title=Accumulation of DNA damage in the aged hematopoietic stem cell compartment |journal=Semin Hematol |volume=54 |issue=1 |pages=12–18 |date=January 2017 |pmid=28088982 |doi=10.1053/j.seminhematol.2016.11.001 |pmc=5242379 |url=}} In healthy humans after 50 years of age, chronological age shows a linear association with DNA damage accumulation in blood mononuclear cells.{{cite journal |vauthors=Vlachogiannis NI, Ntouros PA, Pappa M, Kravvariti E, Kostaki EG, Fragoulis GE, Papanikolaou C, Mavroeidi D, Bournia VK, Panopoulos S, Laskari K, Arida A, Gorgoulis VG, Tektonidou MG, Paraskevis D, Sfikakis PP, Souliotis VL |title=Chronological Age and DNA Damage Accumulation in Blood Mononuclear Cells: A Linear Association in Healthy Humans after 50 Years of Age |journal=Int J Mol Sci |volume=24 |issue=8 |date=April 2023 |page=7148 |pmid=37108309 |doi=10.3390/ijms24087148 |doi-access=free |pmc=10138488 |url=}} Genome-wide profiles of DNA damage can be used as highly accurate predictors of mammalian age.{{cite journal |vauthors=Cao H, Deng B, Song T, Lian J, Xia L, Chu X, Zhang Y, Yang F, Wang C, Cai Y, Diao Y, Kapranov P |title=Genome-wide profiles of DNA damage represent highly accurate predictors of mammalian age |journal=Aging Cell |volume=23 |issue=5 |pages=e14122 |date=May 2024 |pmid=38391092 |doi=10.1111/acel.14122 |pmc=11113270 |url=}}
• Genetic instability: Dogs annually lose approximately 3.3% of the DNA in their heart muscle cells while humans lose approximately 0.6% of their heart muscle DNA each year. These numbers are close to the ratio of the maximum longevities of the two species (120 years vs. 20 years, a 6/1 ratio). The comparative percentage is also similar between the dog and human for yearly DNA loss in the brain and lymphocytes. As stated by lead author, Bernard L. Strehler, "... genetic damage (particularly gene loss) is almost certainly (or probably the) central cause of ageing."{{Cite journal |vauthors=Strehler BL |year=1986 |title=Genetic instability as the primary cause of human aging |journal=Experimental Gerontology |volume=21 |issue=4–5 |pages=283–319 |doi=10.1016/0531-5565(86)90038-0 |pmid=3545872 |s2cid=34431271}}
• Accumulation of waste:
• A buildup of waste products in cells presumably interferes with metabolism. For example, a waste product called lipofuscin is formed by a complex reaction in cells that binds fat to proteins. Lipofuscin may accumulate in the cells as small granules during ageing.{{Cite book |title=Handbook of the Biology of Aging |vauthors=Gavrilov LA, Gavrilova NA |date=2006 |publisher=Academic Press |veditors=Masoro EJ, Austad SN |location=San Diego, CA |pages=3–42 |chapter=Reliability Theory of Aging and Longevity}}{{dubious|date=August 2023}}
• The hallmark of ageing yeast cells appears to be overproduction of certain proteins.
• Autophagy induction can enhance clearance of toxic intracellular waste associated with neurodegenerative diseases and has been comprehensively demonstrated to improve lifespan in yeast, worms, flies, rodents and primates. The situation, however, has been complicated by the identification that autophagy up-regulation can also occur during ageing.{{Cite journal |vauthors=Carroll B, Hewitt G, Korolchuk VI |year=2013 |title=Autophagy and ageing: implications for age-related neurodegenerative diseases |journal=Essays in Biochemistry |volume=55 |pages=119–31 |doi=10.1042/bse0550119 |pmid=24070476 |s2cid=1603760}}
• Wear-and-tear theory: The general idea that changes associated with ageing are the result of chance damage that accumulates over time.
• Accumulation of errors: The idea that ageing results from chance events that escape proofreading mechanisms, which gradually damages the genetic code.{{medical citation needed|date=August 2023}}
• Heterochromatin loss, model of ageing.{{Cite journal |vauthors=Lee JH, Kim EW, Croteau DL, Bohr VA |date=September 2020 |title=Heterochromatin: an epigenetic point of view in aging |journal=Experimental & Molecular Medicine |volume=52 |issue=9 |pages=1466–1474 |doi=10.1038/s12276-020-00497-4 |pmc=8080806 |pmid=32887933 |doi-access=free}}{{Cite journal |vauthors=Tsurumi A, Li WX |date=July 2012 |title=Global heterochromatin loss: a unifying theory of aging? |journal=Epigenetics |volume=7 |issue=7 |pages=680–8 |doi=10.4161/epi.20540 |pmc=3414389 |pmid=22647267}}
• Cross-linkage: The idea that ageing results from accumulation of cross-linked compounds that interfere with normal cell function.{{Cite journal |vauthors=Bjorksten J, Tenhu H |year=1990 |title=The crosslinking theory of aging—added evidence |journal=Experimental Gerontology |volume=25 |issue=2 |pages=91–5 |doi=10.1016/0531-5565(90)90039-5 |pmid=2115005 |s2cid=19115146}}
• Studies of mtDNA mutator mice have shown that increased levels of somatic mtDNA mutations directly can cause a variety of ageing phenotypes. The authors propose that mtDNA mutations lead to respiratory-chain-deficient cells and thence to apoptosis and cell loss. They cast doubt experimentally however on the common assumption that mitochondrial mutations and dysfunction lead to increased generation of reactive oxygen species (ROS).{{Cite journal |vauthors=Trifunovic A, Larsson NG |date=February 2008 |title=Mitochondrial dysfunction as a cause of ageing |journal=Journal of Internal Medicine |volume=263 |issue=2 |pages=167–78 |doi=10.1111/j.1365-2796.2007.01905.x |pmid=18226094 |doi-access=free |s2cid=28396237}}
• Free-radical theory: Damage by free radicals, or more generally reactive oxygen species or oxidative stress, create damage that may give rise to the symptoms we recognise as ageing.{{Cite journal |vauthors=Harman D |date=November 1981 |title=The aging process |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=78 |issue=11 |pages=7124–8 |bibcode=1981PNAS...78.7124H |doi=10.1073/pnas.78.11.7124 |pmc=349208 |pmid=6947277 |doi-access=free}} The effect of calorie restriction may be due to increased formation of free radicals within the mitochondria, causing a secondary induction of increased antioxidant defence capacity.{{Cite journal |vauthors=Schulz TJ, Zarse K, Voigt A, Urban N, Birringer M, Ristow M |date=October 2007 |title=Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress |journal=Cell Metabolism |volume=6 |issue=4 |pages=280–93 |doi=10.1016/j.cmet.2007.08.011 |pmid=17908557 |doi-access=free}}
• Mitochondrial theory of ageing: free radicals produced by mitochondrial activity damage cellular components, leading to ageing.
• DNA oxidation and caloric restriction: Caloric restriction reduces 8-OH-dG DNA damage in organs of ageing rats and mice.{{Cite journal |display-authors=6 |vauthors=Hamilton ML, Van Remmen H, Drake JA, Yang H, Guo ZM, Kewitt K, Walter CA, Richardson A |date=August 2001 |title=Does oxidative damage to DNA increase with age? |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=98 |issue=18 |pages=10469–74 |bibcode=2001PNAS...9810469H |doi=10.1073/pnas.171202698 |pmc=56984 |pmid=11517304 |doi-access=free}}{{Cite journal |vauthors=Wolf FI, Fasanella S, Tedesco B, Cavallini G, Donati A, Bergamini E, Cittadini A |date=March 2005 |title=Peripheral lymphocyte 8-OHdG levels correlate with age-associated increase of tissue oxidative DNA damage in Sprague-Dawley rats. Protective effects of caloric restriction |journal=Experimental Gerontology |volume=40 |issue=3 |pages=181–8 |doi=10.1016/j.exger.2004.11.002 |pmid=15763395 |s2cid=23752647}} Thus, reduction of oxidative DNA damage is associated with a slower rate of ageing and increased lifespan.{{Cite journal |vauthors=Anson RM, Bohr VA |date=October 2000 |title=Mitochondria, oxidative DNA damage, and aging |journal=Journal of the American Aging Association |volume=23 |issue=4 |pages=199–218 |doi=10.1007/s11357-000-0020-y |pmc=3455271 |pmid=23604866}} In a 2021 review article, Vijg stated that "Based on an abundance of evidence, DNA damage is now considered as the single most important driver of the degenerative processes that collectively cause ageing."{{cite journal |vauthors=Vijg J |title=From DNA damage to mutations: All roads lead to aging |journal=Ageing Research Reviews |volume=68 |issue= |pages=101316 |date=July 2021 |pmid=33711511 |pmc=10018438 |doi=10.1016/j.arr.2021.101316}}

{{See also|Life extension}}

The Mediterranean diet is credited with lowering the risk of heart disease and early death.{{Cite journal |display-authors=6 |vauthors=Rees K, Takeda A, Martin N, Ellis L, Wijesekara D, Vepa A, Das A, Hartley L, Stranges S |date=March 2019 |title=Mediterranean-style diet for the primary and secondary prevention of cardiovascular disease |journal=The Cochrane Database of Systematic Reviews |volume=2019 |issue=3 |pages=CD009825 |doi=10.1002/14651858.CD009825.pub3 |pmc=6414510 |pmid=30864165 |collaboration=Cochrane Heart Group}}{{Cite journal |vauthors=Sofi F, Cesari F, Abbate R, Gensini GF, Casini A |date=September 2008 |title=Adherence to Mediterranean diet and health status: meta-analysis |journal=BMJ |volume=337 |issue=sep11 2 |pages=a1344 |doi=10.1136/bmj.a1344 |pmc=2533524 |pmid=18786971}} The major contributors to mortality risk reduction appear to be a higher consumption of vegetables, fish, fruits, nuts and monounsaturated fatty acids, such as by consuming olive oil.{{Cite journal |vauthors=de Gaetano G |date=2016-08-29 |title=Mediterranean diet associated with lower risk of early death in cardiovascular disease patients. European Society of Cardiology |url=https://www.sciencedaily.com/releases/2016/08/160829094040.htm |journal=ScienceDaily}}

As of 2021, there is insufficient clinical evidence that calorie restriction or any dietary practice affects the process of ageing.{{cite journal |vauthors=Lee MB, Hill CM, Bitto A, Kaeberlein M |date=November 2021 |title=Antiaging diets: Separating fact from fiction |journal=Science |volume=374 |issue=6570 |pages=eabe7365 |doi=10.1126/science.abe7365 |pmc=8841109 |pmid=34793210}}

People who participate in moderate to high levels of physical exercise have a lower mortality rate compared to individuals who are not physically active.{{Cite book |last=United States Department of Health And Human Services |url=https://books.google.com/books?id=WZZPc1FmL7QC&q=+United+States.+Department+of+Health.+Physical+activity+and+health:+a+report+of+the+Surgeon+General.+diane+Publishing,+1996.&pg=PA3 |title=Physical activity and health: a report of the Surgeon General |publisher=United States Department of Health and Human Services |year=1996 |isbn=978-1-4289-2794-0}} The majority of the benefits from exercise are achieved with around 3500 metabolic equivalent (MET) minutes per week. For example, climbing stairs 10 minutes, vacuuming 15 minutes, gardening 20 minutes, running 20 minutes, and walking or bicycling for 25 minutes on a daily basis would together achieve about 3000 MET minutes a week.{{Cite journal |display-authors=6 |vauthors=Kyu HH, Bachman VF, Alexander LT, Mumford JE, Afshin A, Estep K, Veerman JL, Delwiche K, Iannarone ML, Moyer ML, Cercy K, Vos T, Murray CJ, Forouzanfar MH |date=August 2016 |title=Physical activity and risk of breast cancer, colon cancer, diabetes, ischemic heart disease, and ischemic stroke events: systematic review and dose-response meta-analysis for the Global Burden of Disease Study 2013 |journal=BMJ |volume=354 |pages=i3857 |doi=10.1136/bmj.i3857 |pmc=4979358 |pmid=27510511}}

Exercise has also been found to be an effective measure to treat declines in neuromuscular function due to age. {{Cite journal |last1=Zhao |first1=Haotian |last2=Cheng |first2=Ruihong |last3=Song |first3=Ge |last4=Teng |first4=Jin |last5=Shen |first5=Siqin |last6=Fu |first6=Xuancheng |last7=Yan |first7=Yi |last8=Liu |first8=Chang |date=January 2022 |title=The Effect of Resistance Training on the Rehabilitation of Elderly Patients with Sarcopenia: A Meta-Analysis |journal=International Journal of Environmental Research and Public Health |language=en |volume=19 |issue=23 |pages=15491 |doi=10.3390/ijerph192315491 |doi-access=free |pmid=36497565 |issn=1660-4601|pmc=9739568 }} A meta-analysis found that resistance training with elastic bands or kettlebells provided significant improvements to grip strength, gait speed, and skeletal muscle mass in patients with sarcopenia. Furthermore, another analysis found that the positive effects of resistance exercise on strength, muscle mass, and motor coordination reduce the risk of falls in the elderly, which is a key factor for living a longer and healthier life. {{Cite journal |last1=Rodrigues |first1=Filipe |last2=Domingos |first2=Christophe |last3=Monteiro |first3=Diogo |last4=Morouço |first4=Pedro |date=January 2022 |title=A Review on Aging, Sarcopenia, Falls, and Resistance Training in Community-Dwelling Older Adults |journal=International Journal of Environmental Research and Public Health |language=en |volume=19 |issue=2 |pages=874 |doi=10.3390/ijerph19020874 |doi-access=free |pmid=35055695 |pmc=8775372 |issn=1660-4601}} In terms of programming, there is no one-size-fits-all approach. General recommendations for improvements to gait speed, strength, and muscle size for reduced fall risk are resistance training programs with two to three 40-60 minute workouts per week, consisting of 1-2 sets of 5-8 repetitions of 2-3 different exercises for each major muscle group, but individual considerations must be taken due to differences in health status, motivation, and accessibility to exercise facilities.

There is also evidence to suggest that exercise of any type may mitigate the degradation of the neuromuscular junction (NMJ) that occurs with age. {{Cite journal |last1=Wang |first1=Qianjin |last2=Cui |first2=Can |last3=Zhang |first3=Ning |last4=Lin |first4=Wujian |last5=Chai |first5=Senlin |last6=Chow |first6=Simon Kwoon-Ho |last7=Wong |first7=Ronald Man Yeung |last8=Hu |first8=Yong |last9=Law |first9=Sheung Wai |last10=Cheung |first10=Wing-Hoi |date=2024-05-01 |title=Effects of physical exercise on neuromuscular junction degeneration during ageing: A systematic review |journal=Journal of Orthopaedic Translation |volume=46 |pages=91–102 |doi=10.1016/j.jot.2024.03.007 |pmid=38817243 |pmc=11137388 |issn=2214-031X}} Current evidence suggests that aerobic exercise causes the most hypertrophy of the NMJ, although resistance training is still somewhat effective. However, further evidence is necessary to identify optimal training protocols for NMJ function and to further understand how exercise affects the mechanisms that cause NMJ degradation.

A meta-analysis showed that loneliness carries a higher mortality risk than smoking.{{Cite journal |vauthors=Holt-Lunstad J, Smith TB, Layton JB |date=July 2010 |title=Social relationships and mortality risk: a meta-analytic review |journal=PLOS Medicine |volume=7 |issue=7 |pages=e1000316 |doi=10.1371/journal.pmed.1000316 |pmc=2910600 |pmid=20668659 |doi-access=free }}

{{main|Aging and society}}{{See also|Gerontology}}{{wiktionary|quadragenarian|quinquagenarian|sexagenarian|septuagenarian|octogenarian|nonagenarian}}

{{Anchor|Dividing the lifespan}}

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File:003 p4 dd.JPG

Different cultures express age in different ways. The age of an adult human is commonly measured in whole years since the day of birth. (The most notable exception{{mdash}}East Asian age reckoning{{mdash}}is becoming less common, particularly in official contexts.) Arbitrary divisions set to mark periods of life may include juvenile (from infancy through childhood, preadolescence, and adolescence), early adulthood, middle adulthood, and late adulthood. Informal{{fact|date=May 2024}} terms include "tweens", "teenagers", "twentysomething", "thirtysomething", etc. as well as "denarian", "vicenarian", "tricenarian", "quadragenarian", etc.

Most legal systems define a specific age for when an individual is allowed or obliged to do particular activities. These age specifications include voting age, drinking age, age of consent, age of majority, age of criminal responsibility, marriageable age, age of candidacy, and mandatory retirement age. Admission to a movie, for instance, may depend on age according to a motion picture rating system. A bus fare might be discounted for the young or old. Each nation, government, and non-governmental organization has different ways of classifying age. In other words, chronological ageing may be distinguished from "social ageing" (cultural age-expectations of how people should act as they grow older) and "biological ageing" (an organism's physical state as it ages).Phillips, Judith, Kristine Ajrouch, and Sarah Hillcoat-Nallétamby (2010) Key Concepts in Social Gerontology. SAGE Publications. {{ISBN|978-1-4462-0428-3}}. pp. 12–13.

Ageism cost the United States $63 billion in one year according to a Yale School of Public Health study.{{Cite journal |vauthors=Levy BR, Slade MD, Chang ES, Kannoth S, Wang SY |date=January 2020 |title=Ageism Amplifies Cost and Prevalence of Health Conditions |journal=The Gerontologist |volume=60 |issue=1 |pages=174–181 |doi=10.1093/geront/gny131 |pmc=7182003 |pmid=30423119 |doi-access=free}} In a UNFPA report about ageing in the 21st century, it highlighted the need to "Develop a new rights-based culture of ageing and a change of mindset and societal attitudes towards ageing and older persons, from welfare recipients to active, contributing members of society". UNFPA said that this "requires, among others, working towards the development of international human rights instruments and their translation into national laws and regulations and affirmative measures that challenge age discrimination and recognise older people as autonomous subjects". Older people's music participation contributes to the maintenance of interpersonal relationships and promoting successful ageing.{{Cite journal |vauthors=LO W |year=2015 |title=The music culture of older adults in Cantonese operatic singing lessons |journal=Ageing and Society |volume=35 |issue=8 |pages=1614–34 |doi=10.1017/S0144686X14000439 |s2cid=144367063}} At the same time, older persons can make contributions to society including caregiving and volunteering. For example, "A study of Bolivian migrants who [had] moved to Spain found that 69% left their children at home, usually with grandparents. In rural China, grandparents care for 38% of children aged under five whose parents have gone to work in cities."

{{See also|Population ageing}}

File:2017 world map, median age by country.svg

Population ageing is the increase in the number and proportion of older people in society. Population ageing has three possible causes: migration, longer life expectancy (decreased death rate) and decreased birth rate. Ageing has a significant impact on society. Young people tend to have fewer legal privileges (if they are below the age of majority), they are more likely to push for political and social change, to develop and adopt new technologies, and to need education. Older people have different requirements from society and government, and frequently have differing values as well, such as for property and pension rights.{{Cite journal |vauthors=Vincent JA |date=December 2005 |title=Understanding generations: political economy and culture in an ageing society |journal=The British Journal of Sociology |volume=56 |issue=4 |pages=579–99 |doi=10.1111/j.1468-4446.2005.00084.x |pmid=16309437 |s2cid=1775770}}

In the 21st century, one of the most significant population trends is ageing.{{Cite web |year=2002 |title=Population Ageing and Development |url=http://www.unfpa.org/publications/population-ageing-and-development-0 |publisher=UNFPA}} Currently, over 11% of the world's current population are people aged 60 and older and the United Nations Population Fund (UNFPA) estimates that by 2050 that number will rise to approximately 22%.{{Cite web |year=2012 |title=Ageing in the Twenty-First Century |url=http://www.unfpa.org/publications/ageing-twenty-first-century |publisher=UNFPA}} Ageing has occurred due to development which has enabled better nutrition, sanitation, health care, education and economic well-being. Consequently, fertility rates have continued to decline and life expectancy has risen. Life expectancy at birth is over 80 now in 33 countries. Ageing is a "global phenomenon", that is occurring fastest in developing countries, including those with large youth populations, and poses social and economic challenges to the work which can be overcome with "the right set of policies to equip individuals, families and societies to address these challenges and to reap its benefits".{{Cite web |title=Ageing |url=http://www.unfpa.org/ageing |website=unfpa.org |publisher=UNFPA – United Nations Population Fund}}

As life expectancy rises and birth rates decline in developed countries, the median age rises accordingly. According to the United Nations, this process is taking place in nearly every country in the world.{{Cite web |title=UN Human Development Report 2005 |url=http://hdr.undp.org/en/media/HDR05_complete.pdf |archive-url=https://web.archive.org/web/20080527203423/http://hdr.undp.org/en/media/hdr05_complete.pdf |archive-date=27 May 2008 |access-date=7 October 2010 |publisher=United Nations Development Programme}} A rising median age can have significant social and economic implications, as the workforce gets progressively older and the number of old workers and retirees grows relative to the number of young workers. Older people generally incur more health-related costs than do younger people in the workplace and can also cost more in worker's compensation and pension liabilities.{{Cite web |title=Safer and Healthier at Any Age: Strategies for an Aging Workforce |url=http://blogs.cdc.gov/niosh-science-blog/2012/07/agingworkforce/ |access-date=6 August 2012 |website=NIOSH Science Blog |publisher=National Institute for Occupational Safety and Health |vauthors=Chosewood LC|date=19 July 2012 }} In most developed countries an older workforce is somewhat inevitable. In the United States for instance, the Bureau of Labor Statistics estimates that one in four American workers will be 55 or older by 2020.{{update inline|date=March 2022}}

Among the most urgent concerns of older persons worldwide is income security. This poses challenges for governments with ageing populations to ensure investments in pension systems continues to provide economic independence and reduce poverty in old age. These challenges vary for developing and developed countries. UNFPA stated that, "Sustainability of these systems is of particular concern, particularly in developed countries, while social protection and old-age pension coverage remain a challenge for developing countries, where a large proportion of the labour force is found in the informal sector."

The global economic crisis has increased financial pressure to ensure economic security and access to health care in old age. To elevate this pressure "social protection floors must be implemented in order to guarantee income security and access to essential health and social services for all older persons and provide a safety net that contributes to the postponement of disability and prevention of impoverishment in old age".

It has been argued that population ageing has undermined economic development{{Cite journal |vauthors=Basakha M, Yavari K, Sadeghi H, Naseri A |year=2015 |title=Population Aging And Iran's Non-Oil Economic Growth |url=http://payavard.tums.ac.ir/browse.php?a_code=A-10-1-113&sid=1&slc_lang=en |journal=Payavard Salamat |volume=9 |issue=2 |pages=131–46}} and can lead to lower inflation because elderly individuals care especially strongly about the value of their pensions and savings. Evidence suggests that pensions, while making a difference to the well-being of older persons, also benefit entire families especially in times of crisis when there may be a shortage or loss of employment within households. A study by the Australian Government in 2003 estimated that "women between the ages of 65 and 74 years contribute A$16 billion per year in unpaid caregiving and voluntary work. Similarly, men in the same age group contributed A$10 billion per year."

Due to increasing share of the elderly in the population, health care expenditures will continue to grow relative to the economy in coming decades. This has been considered as a negative phenomenon and effective strategies like labour productivity enhancement should be considered to deal with negative consequences of ageing.{{Cite journal |vauthors=Basakha M, Yavari K, Sadeghi H, Naseri A |year=2014 |title=Health care cost disease as a threat to Iranian aging society |url=http://jrhs.umsha.ac.ir/index.php/JRHS/article/view/1109/pdf |journal=Journal of Research in Health Sciences |volume=14 |issue=2 |pages=152–6 |pmid=24728752}}

File:Menneske Aldrene (C. W. Eckersberg).png: Ages of Man]]

In the field of sociology and mental health, ageing is seen in five different views: ageing as maturity, ageing as decline, ageing as a life-cycle event, ageing as generation, and ageing as survival.{{Cite book |title=A Handbook for the Study of Mental Health |vauthors=Scheid TL, Brown TN |date=2010 |publisher=Cambridge University Press |edition=Second |location=New York}} Positive correlates with ageing often include economics, employment, marriage, children, education, and sense of control, as well as many others. The social science of ageing includes disengagement theory, activity theory, selectivity theory, and continuity theory. Retirement, a common transition faced by the elderly, may have both positive and negative consequences.{{Cite book |title=Adult development and aging |vauthors=Panek PE, Hayslip B |publisher=Harper & Row |year=1989 |isbn=978-0-06-045012-0 |location=San Francisco}}{{page needed|date=November 2013}} As cyborgs currently are on the rise{{cite book |last1=Barfield |first1=Woodrow |title=Cyber-humans : our future with machines |date=2015 |location=Cham |isbn=978-3-319-25048-9 }} some theorists argue there is a need to develop new definitions of ageing and for instance a bio-techno-social definition of ageing has been suggested.{{Cite journal |vauthors=Wejbrandt A |date=December 2014 |title=Defining aging in cyborgs: a bio-techno-social definition of aging |journal=Journal of Aging Studies |volume=31 |pages=104–9 |doi=10.1016/j.jaging.2014.09.003 |pmid=25456627}}

There is a current debate as to whether or not the pursuit of longevity and the postponement of senescence are cost-effective health care goals given finite health care resources. Because of the accumulated infirmities of old age, bioethicist Ezekiel Emanuel, opines that the pursuit of longevity via the compression of morbidity hypothesis is a "fantasy" and that human life is not worth living after age 75; longevity then should not be a goal of health care policy.{{Cite journal |last=Emmanuel EJ |date=October 2014 |title=Why I hope to die at 75: An argument that society and families – and you – will be better off if nature takes its course swiftly and promptly |url=https://www.theatlantic.com/features/archive/2014/09/why-i-hope-to-die-at-75/379329/ |journal=The Atlantic |access-date=7 April 2015}} This opinion has been contested by neurosurgeon and medical ethicist Miguel Faria, who states that life can be worthwhile during old age, and that longevity should be pursued in association with the attainment of quality of life.{{Cite journal |vauthors=Faria MA |year=2015 |title=Bioethics and why I hope to live beyond age 75 attaining wisdom!: A rebuttal to Dr. Ezekiel Emanuel's 75 age limit |journal=Surgical Neurology International |volume=6 |pages=35 |doi=10.4103/2152-7806.152733 |pmc=4360549 |pmid=25789197 |doi-access=free }} Faria claims that postponement of senescence as well as happiness and wisdom can be attained in old age in a large proportion of those who lead healthy lifestyles and remain intellectually active.{{Cite journal |vauthors=Faria MA |date=2015 |title=Longevity and compression of morbidity from a neuroscience perspective: Do we have a duty to die by a certain age? |journal=Surgical Neurology International |volume=6 |pages=49 |doi=10.4103/2152-7806.154273 |pmc=4392568 |pmid=25883841 |doi-access=free }}

File:Healthcare expenditures in Japan by Age.svg)]]

With age inevitable biological changes occur that increase the risk of illness and disability. UNFPA states that:

"A life-cycle approach to health care – one that starts early, continues through the reproductive years and lasts into old age – is essential for the physical and emotional well-being of older persons, and, indeed, all people. Public policies and programmes should additionally address the needs of older impoverished people who cannot afford health care."

Many societies in Western Europe and Japan have ageing populations. While the effects on society are complex, there is a concern about the impact on health care demand. The large number of suggestions in the literature for specific interventions to cope with the expected increase in demand for long-term care in ageing societies can be organized under four headings: improve system performance; redesign service delivery; support informal caregivers; and shift demographic parameters.{{Cite journal |vauthors=Saltman RB, Dubois HF, Chawla M |year=2006 |title=The impact of aging on long-term care in Europe and some potential policy responses |journal=International Journal of Health Services |volume=36 |issue=4 |pages=719–46 |doi=10.2190/AUL1-4LAM-4VNB-3YH0 |pmid=17175843 |s2cid=45396303}}

However, the annual growth in national health spending is not mainly due to increasing demand from ageing populations, but rather has been driven by rising incomes, costly new medical technology, a shortage of health care workers and informational asymmetries between providers and patients.{{Cite journal |vauthors=Reinhardt UE |year=2003 |title=Does the aging of the population really drive the demand for health care? |journal=Health Affairs |volume=22 |issue=6 |pages=27–39 |doi=10.1377/hlthaff.22.6.27 |pmid=14649430 |doi-access=free}} A number of health problems become more prevalent as people get older. These include mental health problems as well as physical health problems, especially dementia.

It has been estimated that population ageing only explains 0.2 percentage points of the annual growth rate in medical spending of 4.3% since 1970. In addition, certain reforms to the Medicare system in the United States decreased elderly spending on home health care by 12.5% per year between 1996 and 2000.{{Cite journal |vauthors=Meara E, White C, Cutler DM |year=2004 |title=Trends in medical spending by age, 1963–2000 |journal=Health Affairs |volume=23 |issue=4 |pages=176–83 |doi=10.1377/hlthaff.23.4.176 |pmid=15318578 |doi-access=free}}

Beauty standards have evolved over time, and as scientific research in cosmeceuticals, cosmetic products seen to have medicinal benefits like anti-ageing creams, has increased, the industry has also expanded; the kinds of products they produce (such as serums and creams) have gradually gained popularity and become a part of many people's personal care routine.{{Cite journal |vauthors=Kattimani V, Tiwari RV, Gufran K, Wasan B, Shilpa PH, Khader AA |date=March 2019 |title=Botulinum Toxin Application in Facial Esthetics and Recent Treatment Indications (2013–2018) |journal=Journal of International Society of Preventive & Community Dentistry |volume=9 |issue=2 |pages=99–105 |doi=10.4103/jispcd.JISPCD_430_18 |pmc=6489509 |pmid=31058058 |quote=Standards of beauty have changed through centuries with increased awareness about esthetics. |doi-access=free }}

The increase in demand for cosmeceuticals has led scientists to find ingredients for these products in unorthodox places. For example, the secretion of cryptomphalus aspersa (or brown garden snail) has been found to have antioxidant properties, increase skin cell proliferation, and increase extracellular proteins such as collagen and fibronectin (important proteins for cell proliferation).{{Cite journal |vauthors=Juhász ML, Levin MK, Marmur ES |date=June 2018 |title=The use of natural ingredients in innovative Korean cosmeceuticals |journal=Journal of Cosmetic Dermatology |volume=17 |issue=3 |pages=305–312 |doi=10.1111/jocd.12492 |pmid=29363245 |s2cid=25982162}} {{verify source |date=August 2019 |reason=This ref was deleted (Special:Diff/909069547) by a bug in VisualEditor and later restored by a bot from the original cite at Special:Permalink/909069468 cite No. 3 – please verify the cite's accuracy and remove this {verify source} template. User:GreenC bot/Job 18}} Another substance used to prevent the physical manifestations of ageing is onobotulinumtoxinA, the toxin injected for Botox.{{Cite web |title=Botox injections – Mayo Clinic |url=https://www.mayoclinic.org/tests-procedures/botox/about/pac-20384658#:~:text=Botox%20injections%20are%20relatively%20safe,Headache%20or%20flu-like%20symptoms |access-date=2021-03-12 |website=www.mayoclinic.org}}

In some cultures, old age is celebrated and honoured. In Korea, for example, a special party called hwangap is held to celebrate and congratulate an individual for turning 60 years old.{{Cite web |title=Korea – Birthday Celebrations |url=http://www.asianinfo.org/asianinfo/korea/cel/birthday_celebrations.htm |access-date=2021-03-12 |website=www.asianinfo.org}} In China, respect for elderly is often the basis for how a community is organized and has been at the foundation of Chinese culture and morality for thousands of years. Older people are respected for their wisdom and most important decisions have traditionally not been made without consulting them. This is a similar case for most Asian countries such as the Philippines, Thailand, Vietnam, Singapore, etc.

Positive self-perceptions of ageing are associated with better mental and physical health and well-being.{{Cite journal |display-authors=6 |vauthors=Sabatini S, Silarova B, Martyr A, Collins R, Ballard C, Anstey KJ, Kim S, Clare L |date=August 2020 |title=Associations of Awareness of Age-Related Change With Emotional and Physical Well-being: A Systematic Review and Meta-analysis |journal=The Gerontologist |volume=60 |issue=6 |pages=e477–e490 |doi=10.1093/geront/gnz101 |pmc=7427487 |pmid=31350849 |doi-access=free}} Positive self-perception of health has been correlated with higher well-being and reduced mortality among the elderly.{{Cite journal |vauthors=Idler EL |year=2003 |title=Discussion: Gender Differences in Self-Rated Health, in Mortality, and in the Relationship Between the Two |journal=The Gerontologist |volume=43 |issue=3 |pages=372–75 |doi=10.1093/geront/43.3.372 |doi-access=free}}{{Cite journal |vauthors=Deeg DJ, Bath PA |date=June 2003 |title=Self-rated health, gender, and mortality in older persons: introduction to a special section |journal=The Gerontologist |volume=43 |issue=3 |pages=369–71 |doi=10.1093/geront/43.3.369 |pmid=12810900 |doi-access=free}} Various reasons have been proposed for this association; people who are objectively healthy may naturally rate their health better as than that of their ill counterparts, though this link has been observed even in studies which have controlled for socioeconomic status, psychological functioning and health status.{{Cite journal |vauthors=Benyamini Y, Blumstein T, Lusky A, Modan B |date=June 2003 |title=Gender differences in the self-rated health-mortality association: is it poor self-rated health that predicts mortality or excellent self-rated health that predicts survival? |journal=The Gerontologist |volume=43 |issue=3 |pages=396–405; discussion 372–5 |doi=10.1093/geront/43.3.396 |pmid=12810904 |doi-access=free}} This finding is generally stronger for men than women, though this relationship is not universal across all studies and may only be true in some circumstances.

As people age, subjective health remains relatively stable, even though objective health worsens.{{Cite journal |vauthors=Kunzmann U, Little TD, Smith J |date=September 2000 |title=Is age-related stability of subjective well-being a paradox? Cross-sectional and longitudinal evidence from the Berlin Aging Study |journal=Psychology and Aging |volume=15 |issue=3 |pages=511–26 |doi=10.1037/0882-7974.15.3.511 |pmid=11014714}} In fact, perceived health improves with age when objective health is controlled in the equation.{{Cite journal |vauthors=Jylhä M, Guralnik JM, Balfour J, Fried LP |date=October 2001 |title=Walking difficulty, walking speed, and age as predictors of self-rated health: the women's health and aging study |journal=The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences |volume=56 |issue=10 |pages=M609-17 |doi=10.1093/gerona/56.10.m609 |pmid=11584033 |doi-access=free}} This phenomenon is known as the "paradox of ageing". This may be a result of social comparison;{{Cite book |url=https://archive.org/details/developmentalreg0000heck |title=Developmental Regulation in Adulthood: Age-Normative and Sociostructural Constraints as Adaptive Challenges |vauthors=Heckhausen J |date=1999 |publisher=Cambridge University Press |isbn=978-0-521-02713-7 |url-access=registration}} for instance, the older people get, the more they may consider themselves in better health than their same-aged peers.{{Cite journal |vauthors=Sargent-Cox KA, Anstey KJ, Luszcz MA |date=September 2008 |title=Determinants of self-rated health items with different points of reference: implications for health measurement of older adults |journal=Journal of Aging and Health |volume=20 |issue=6 |pages=739–61 |doi=10.1177/0898264308321035 |pmid=18625760 |s2cid=34866893}} Elderly people often associate their functional and physical decline with the normal ageing process.{{Cite journal |vauthors=Idler EL |date=November 1993 |title=Age differences in self-assessments of health: age changes, cohort differences, or survivorship? |journal=Journal of Gerontology |volume=48 |issue=6 |pages=S289-300 |doi=10.1093/geronj/48.6.s289 |pmid=8228003}}{{Cite journal |vauthors=Williamson JD, Fried LP |date=December 1996 |title=Characterization of older adults who attribute functional decrements to "old age" |journal=Journal of the American Geriatrics Society |volume=44 |issue=12 |pages=1429–34 |doi=10.1111/j.1532-5415.1996.tb04066.x |pmid=8951311 |s2cid=21027678}}

One way to help younger people experience what it feels like to be older is through an ageing suit. There are several different kinds of suits including the GERT (named as a reference to gerontology), the R70i exoskeleton, and the AGNES (Age Gain Now Empathy Suit) suits.{{Cite web |title=40 Years In 5 Minutes: Age Simulation Suit Aims To Increase Empathy In Building Design |url=https://www.wbur.org/hereandnow/2019/06/03/age-simulation-suit |access-date=2021-03-12 |website=www.wbur.org |date=3 June 2019 |language=en}}{{Cite web |date=7 January 2016 |title=Hands on: Genworth R70i Exoskeleton |url=https://www.digitaltrends.com/cool-tech/genworth-r70i-exoskeleton/ |url-status=live |archive-url=https://web.archive.org/web/20160108065559/http://www.digitaltrends.com/cool-tech/genworth-r70i-exoskeleton/ |archive-date=8 January 2016 |access-date=12 March 2021 |website=digitaltrends |vauthors=Prindle D}}{{Cite web |title=AGNES (Age Gain Now Empathy System) {{!}} MIT AgeLab |url=https://agelab.mit.edu/agnes-age-gain-now-empathy-system#:~:text=AGNES%20is%20a%20suit%20worn,physical%20challenges%20associated%20with%20aging |url-status=dead |archive-url=https://web.archive.org/web/20210406035347/https://agelab.mit.edu/agnes-age-gain-now-empathy-system#:~:text=AGNES%20is%20a%20suit%20worn,physical%20challenges%20associated%20with%20aging |archive-date=6 April 2021 |access-date=2021-03-12 |website=agelab.mit.edu}} These suits create the feelings of the effects of ageing by adding extra weight and increased pressure in certain points like the wrists, ankles and other joints. In addition, the various suits have different ways to impair vision and hearing to simulate the loss of these senses. To create the loss of feeling in hands that the elderly experience, special gloves are a part of the uniforms.

Use of these suits may help to increase the amount of empathy felt for the elderly and could be considered particularly useful for those who are either learning about ageing, or those who work with the elderly, such as nurses or care centre staff.

Design is another field that could benefit from the empathy these suits may cause. When designers understand what it feels like to have the impairments of old age, they can better design buildings, packaging, or even tools to help with the simple day-to-day tasks that are more difficult with less dexterity. Designing with the elderly in mind may help to reduce the negative feelings that are associated with the loss of abilities that the elderly face.

The healthy ageing framework, proposed by the World Health Organization {{Cite book |last=World Health Organization |url=https://apps.who.int/iris/handle/10665/186463 |title=World report on ageing and health |date=2015 |publisher=World Health Organization |hdl=10665/186463 |isbn=978-92-4-156504-2 |language=en}} operationalizes health as functional ability, which results from the interactions of intrinsic capacity and the environments.

Intrinsic capacity is a construct encompassing people's physical and mental abilities which can be drawn upon during ageing. Intrinsic capacity comprises the domains of: cognition, locomotion, vitality/nutrition, psychological and sensory (visual and hearing). {{Cite journal |last1=González-Bautista |first1=Emmanuel |last2=de Souto Barreto |first2=Philipe |last3=Andrieu |first3=Sandrine |last4=Rolland |first4=Yves |last5=Vellas |first5=Bruno |author66=MAPT/DSA group |display-authors=3 |date=August 2021 |title=Screening for intrinsic capacity impairments as markers of increased risk of frailty and disability in the context of integrated care for older people: Secondary analysis of MAPT |url=https://pubmed.ncbi.nlm.nih.gov/34274071 |journal=Maturitas |volume=150 |pages=1–6 |doi=10.1016/j.maturitas.2021.05.011 |issn=1873-4111 |pmid=34274071}}

A recent study found four "profiles" or "statuses" of intrinsic capacity among older adults, namely high IC (43% at baseline), low deterioration with impaired locomotion (17%), high deterioration without cognitive impairment (22%) and high deterioration with cognitive impairment (18%). Over half of the study sample remained in the same status at baseline and follow-up (61%). Around one-fourth of participants transitioned from the high IC to the low deterioration status, and only 3% of the participants improved their status. Interestingly, the probability of improvement was observed in the status of high deterioration. Participants in the latent statuses of low and high levels of deterioration had a significantly higher risk of frailty, disability and dementia than their high IC counterparts.{{Cite journal |last1=Gonzalez-Bautista |first1=Emmanuel |last2=Llibre-Guerra |first2=Jorge Jesus |last3=Sosa |first3=Ana L |last4=Acosta |first4=Isaac |last5=Andrieu |first5=Sandrine |last6=Acosta |first6=Daisy |last7=Llibre-Rodríguez |first7=Juan de Jesús |last8=Prina |first8=Matthew |display-authors=3 |date=2023-07-01 |title=Exploring the natural history of intrinsic capacity impairments: longitudinal patterns in the 10/66 study |journal=Age and Ageing |language=en |volume=52 |issue=7 |doi=10.1093/ageing/afad137 |issn=0002-0729 |pmc=10387229 |pmid=37517058}}

The concept of successful aging can be traced back to the 1950s and was popularized in the 1980s. Traditional definitions of successful aging have emphasized absence of physical and cognitive disabilities.{{Cite book |title=Successful Aging |vauthors=Baltes PB, Baltes MM |year=1990 |isbn=978-0-511-66568-4 |veditors=Baltes PB, Baltes MM |pages=1–34 |chapter=Psychological perspectives on successful aging: The model of selective optimization with compensation |doi=10.1017/CBO9780511665684.003}} In their 1987 article, Rowe and Kahn characterized successful aging as involving three components: a) freedom from disease and disability, b) high cognitive and physical functioning, and c) social and productive engagement.{{Cite journal |vauthors=Rowe JW, Kahn RL |date=July 1987 |title=Human aging: usual and successful |journal=Science |volume=237 |issue=4811 |pages=143–9 |bibcode=1987Sci...237..143R |doi=10.1126/science.3299702 |pmid=3299702}} The study cited previous was also done back in 1987 and therefore, these factors associated with successful aging have probably been changed. With the current knowledge, scientists started to focus on learning about the effect spirituality in successful aging. There are some differences in cultures as to which of these components are the most important. Most often across cultures, social engagement was the most highly rated but depending on the culture the definition of successful aging changes.{{Cite journal |vauthors=Jensen A, Claunch K, Verdeja M, Dungan M, Goates M, Thacker E |date=2018-11-11 |title=Successful Aging: Cross-Cultural Comparison of Older Adults' Lay Perspectives |journal=Innovation in Aging |volume=2 |issue=Suppl 1 |pages=167 |doi=10.1093/geroni/igy023.601 |issn=2399-5300 |pmc=6229246}}

The ancient Greek dramatist Euripides (5th century BC) describes the multiple-headed mythological monster Hydra as having a regenerative capacity which makes it immortal, which is the historical background to the name of the biological genus Hydra. The Book of Job (c. 6th century BC) describes the human lifespan as inherently limited and makes a comparison with the innate immortality that a felled tree may have when undergoing vegetative regeneration:{{quote|A man's days are numbered. You know the number of his months. He cannot live longer than the time You have set. So now look away from him that he may rest, until he has lived the time set for him like a man paid to work. For there is hope for a tree, when it is cut down, that it will grow again, and that its branches will not stop growing.{{bibleverse|Job|14:5-7|NLV}}: New Life Version}}

{{div col|colwidth=18em}}

• Ageing brain
• Ageing movement control
• Ageing of Europe
• Ageing studies
• Anti-ageing movement
• Biodemography of human longevity
• Biogerontology
• Biological immortality
• Biomarkers of ageing
• Clinical geropsychology
• Death
• DNA damage theory of aging
• Epigenetic clock
• Evolution of ageing
• Genetics of ageing
• Gerontechnology
• Gerontology
• Gerascophobia
• List of life extension-related topics
• Longevity
• Mitochondrial theory of ageing
• Neuroscience of ageing
• Old age
• Old person smell
• Particulates
• Pollutants
• Population ageing
• Progeria
• Rejuvenation
• Stem cell theory of ageing
• Supercentenarian
• Thermoregulation in humans
• Transgenerational design

{{Div col end}}

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{{Developmental biology}}

{{Humandevelopment}}

{{Longevity}}

{{Authority control}}

Category:Gerontology

Category:Old age