life expectancy

The earliest documented work on life expectancy was done in the 1660s by John Graunt,{{cite book|vauthors=Sutherland I|title=Encyclopedia of Biostatistics|date=15 July 2005|isbn=978-0-470-84907-1|pages=1–2|chapter=Graunt, John|doi=10.1002/0470011815.b2a17055}} Christiaan Huygens, and Lodewijck Huygens.{{cite book|vauthors=Johnson S|author-link=Steven Johnson (author)|title=Extra Life|publisher=Riverhead Books|year=2021|isbn=978-0-525-53885-1|edition=1st|pages=15}}

The longest verified lifespan for any human is that of French woman Jeanne Calment, who is verified as having lived to age 122 years, 164 days, between 21 February 1875 and 4 August 1997. This is referred to as the "maximum life span", which is the upper boundary of life, the maximum number of years any human is known to have lived. Although maximum life expectancy is around 125 years, genetic enhancements could allow us to live for a maximum of 245 years, according to InsideTracker.{{cite book|vauthors=Santrock J|date=2007|title=Life Expectancy. A Topical Approach to: Life-Span Development|pages=128–132|location=New York, New York|publisher=The McGraw-Hill Companies, Inc.|isbn=978-0-07-313376-8}} According to a study by biologists Bryan G. Hughes and Siegfried Hekimi, there is no evidence for a limit on human lifespan.{{cite press release|date=28 June 2017|title=No detectable limit to how long people can live|url=https://www.sciencedaily.com/releases/2017/06/170628131500.htm|publisher=Science Daily|access-date=4 July 2017}}{{cite journal|vauthors=Hughes BG, Hekimi S|title=Many possible maximum lifespan trajectories|journal=Nature|volume=546|issue=7660|pages=E8–E9|date=June 2017|pmid=28658230|doi=10.1038/nature22786|s2cid=4464500|bibcode=2017Natur.546E...8H}} However, this view has been questioned on the basis of error patterns.{{cite journal|vauthors=Newman SJ|title=Errors as a primary cause of late-life mortality deceleration and plateaus|journal=PLOS Biology|volume=16|issue=12|pages=e2006776|date=December 2018|pmid=30571676|pmc=6301557|doi=10.1371/journal.pbio.2006776|doi-access=free}} A theoretical study shows that the maximum life expectancy at birth is limited by the human life characteristic value δ, which is around 104 years.{{Cite journal|last=Liu|first=Xiaoping|date=December 2015|title=Life equations for the senescence process|journal=Biochemistry and Biophysics Reports|language=en|volume=4|pages=228–233|doi=10.1016/j.bbrep.2015.09.020|pmc=5669524|pmid=29124208}}

{{further|Longevity|List of countries by past life expectancy}}

The following information is derived from the 1961 Encyclopædia Britannica and other sources, some with questionable accuracy. Unless otherwise stated, it represents estimates of the life expectancies of the world population as a whole. In many instances, life expectancy varied considerably according to class and gender.

Life expectancy at birth takes account of infant mortality and child mortality but not prenatal mortality.

English life expectancy at birth averaged about 36 years in the 17th and 18th centuries, one of the highest levels in the world although infant and child mortality remained higher than in later periods. Life expectancy was under 25 years in the early Colony of Virginia,{{cite web|title=Medicine & Health|url=http://www.stratfordhall.org/educational-resources/teacher-resources/medicine-health/|work=Stratfordhall.org|archive-url=https://web.archive.org/web/20200215062621/http://stratfordhall.org/educational-resources/teacher-resources/medicine-health/|archive-date=15 February 2020}} and in seventeenth-century New England, about 40% died before reaching adulthood.{{cite web|url=http://www.digitalhistory.uh.edu/historyonline/usdeath.cfm|title=Death in Early America|archive-url=https://web.archive.org/web/20101230203658/http://www.digitalhistory.uh.edu/historyonline/usdeath.cfm|archive-date=30 December 2010|work=Digital History}} During the Industrial Revolution, the life expectancy of children increased dramatically.{{cite encyclopedia|url=https://www.britannica.com/EBchecked/topic/387301/modernization/12022/Population-change|title=Population Change Modernization|encyclopedia=Encyclopædia Britannica|date=25 May 2024}} Recorded deaths among children under the age of 5 years fell in London from 74.5% of the recorded births in 1730–49 to 31.8% in 1810–29,{{cite book|vauthors=Buer MC|title=Health, Wealth and Population in the Early Days of the Industrial Revolution|location=London|publisher=George Routledge & Sons|date=1926|page=30|isbn=978-0-415-38218-2}}{{cite web|url=https://www.bbc.co.uk/history/british/victorians/foundling_01.shtml|publisher=BBC|title=History—The Foundling Hospital|date=1 May 2001}} though this overstates mortality and its fall because of net immigration (hence more dying in the metropolis than were born there) and incomplete registration (particularly of births, and especially in the earlier period). English life expectancy at birth reached 41 years in the 1840s, 43 in the 1870s and 46 in the 1890s, though infant mortality remained at around 150 per thousand throughout this period.

File:Life expectancy in 1800, 1950, and 2015.png]]

Public health measures are credited with much of the recent increase in life expectancy. During the 20th century, despite a brief drop due to the 1918 flu pandemic,{{cite web|url=http://www.gapminder.org/world/#$majorMode=chart$is;shi=t;ly=2003;lb=f;il=t;fs=11;al=30;stl=t;st=t;nsl=t;se=t$wst;tts=C$ts;sp=5.59290322580644;ti=1918$zpv;v=0$inc_x;mmid=XCOORDS;iid=phAwcNAVuyj1jiMAkmq1iMg;by=ind$inc_y;mmid=YCOORDS;iid=phAwcNAVuyj2tPLxKvvnNPA;by=ind$inc_s;uniValue=8.21;iid=phAwcNAVuyj0XOoBL_n5tAQ;by=ind$inc_c;uniValue=255;gid=CATID0;by=grp$map_x;scale=log;dataMin=194;dataMax=96846$map_y;scale=lin;dataMin=23;dataMax=86$map_s;sma=49;smi=2.65$cd;bd=0$inds=;modified=75|title=Gapminder World|publisher=Gapminder Foundation}} the average lifespan in the United States increased by more than 30 years, of which 25 years can be attributed to advances in public health.{{cite journal|vauthors=CDC|title=Ten great public health achievements—United States, 1900–1999|journal=MMWR. Morbidity and Mortality Weekly Report|volume=48|issue=12|pages=241–243|date=April 1999|pmid=10220250|url=http://cdc.gov/mmwr/preview/mmwrhtml/00056796.htm}} [http://jama.ama-assn.org/cgi/content/full/281/16/1481 Reprinted] in: {{cite journal|vauthors=|title=From the Centers for Disease Control and Prevention. Ten great public health achievements—United States, 1900–1999|journal=JAMA|volume=281|issue=16|pages=1481|date=April 1999|pmid=10227303|doi=10.1001/jama.281.16.1481|s2cid=2030845|doi-access=}}

{{further|List of countries by life expectancy}}There are great variations in life expectancy between different parts of the world, mostly caused by differences in public health, medical care, and diet.{{Cite journal |last=Worthy |first=L. D. |last2=Lavigne |first2=T. |last3=Romero |first3=F. |date=2020-07-27 |title=Life Expectancy |url=https://openbooks.braou.ac.in/culturepsychology/chapter/life-expectancy/ |language=en}}

Human beings are expected to live on average 60 years in Eswatini{{cite web|url=https://www.cia.gov/the-world-factbook/countries/eswatini/|title=The World Factbook – Central Intelligence Agency|date=4 November 2021}} and 82.6 years in Japan.{{efn|Japan's recorded life expectancy may have been very slightly increased by counting many infant deaths as stillborn.{{cite journal|vauthors=Coale AJ, Banister J|date=December 1996|title=Five decades of missing females in China|journal=Proceedings of the American Philosophical Society|volume=140|issue=4|pages=421–450|jstor=987286|author-link=Ansley J. Coale}} Also printed as {{cite journal|vauthors=Coale AJ, Banister J|title=Five decades of missing females in China|journal=Demography|volume=31|issue=3|pages=459–479|date=August 1994|pmid=7828766|doi=10.2307/2061752|s2cid=24724998|doi-access=free|jstor=2061752}}

}} An analysis published in 2011 in The Lancet attributes Japanese life expectancy to equal opportunities, excellent public health, and a healthy diet.{{cite news|url=https://www.theguardian.com/world/2011/aug/30/japan-life-expectancy-factors|title=Japan's life expectancy 'down to equality and public health measures'|work=The Guardian|date=30 August 2011|access-date=31 August 2011|vauthors=Boseley S|location=London|quote=Japan has the highest life expectancy in the world but the reasons says an analysis, are as much to do with equality and public health measures as diet.... According to a paper in a Lancet series on healthcare in Japan....}}{{cite journal|vauthors=Ikeda N, Saito E, Kondo N, Inoue M, Ikeda S, Satoh T, Wada K, Stickley A, Katanoda K, Mizoue T, Noda M, Iso H, Fujino Y, Sobue T, Tsugane S, Naghavi M, Ezzati M, Shibuya K|title=What has made the population of Japan healthy?|journal=Lancet|volume=378|issue=9796|pages=1094–1105|date=September 2011|pmid=21885105|doi=10.1016/S0140-6736(11)61055-6|quote=Reduction in health inequalities with improved average population health was partly attributable to equal educational opportunities and financial access to care.|s2cid=33124920}}

The World Health Organization announced that the COVID-19 pandemic reversed the trend of steady gain in life expectancy at birth. The pandemic wiped out nearly a decade of progress in improving life expectancy.{{cite news|title=COVID-19 eliminated a decade of progress in global level of life expectancy|url=https://www.who.int/news/item/24-05-2024-covid-19-eliminated-a-decade-of-progress-in-global-level-of-life-expectancy|access-date=3 July 2024|publisher=World Health Organization|date=24 May 2024}}

File:Comparison subsaharan life expectancy.svg{{cite web|url=http://data.worldbank.org/indicator/SP.DYN.LE00.IN/countries/1W|title=Life expectancy at birth, total (years)—Data|publisher=World Bank Group}}]]

During the last 200 years, African countries have generally not had the same improvements in mortality rates that have been enjoyed by countries in Asia, Latin America, and Europe.{{cite web|title=Wealth & Health of Nations|url=http://www.gapminder.org/world/#$majorMode=chart$is;shi=t;ly=2003;lb=f;il=t;fs=11;al=30;stl=t;st=t;nsl=t;se=t$wst;tts=C$ts;sp=5.59290322580644;ti=2013$zpv;v=0$inc_x;mmid=XCOORDS;iid=phAwcNAVuyj1jiMAkmq1iMg;by=ind$inc_y;mmid=YCOORDS;iid=phAwcNAVuyj2tPLxKvvnNPA;by=ind$inc_s;uniValue=8.21;iid=phAwcNAVuyj0XOoBL_n5tAQ;by=ind$inc_c;uniValue=255;gid=CATID0;by=grp$map_x;scale=log;dataMin=194;dataMax=96846$map_y;scale=lin;dataMin=23;dataMax=86$map_s;sma=49;smi=2.65$cd;bd=0$inds=;example=75|access-date=26 June 2015|publisher=Gapminder Foundation}}{{cite web|date=31 August 2022|title=Life Expectancy in the U.S. Dropped for the Second Year in a Row in 2021|url=https://www.cdc.gov/nchs/pressroom/nchs_press_releases/2022/20220831.htm|access-date=31 August 2022|website=Centers for Disease Control and Prevention}} This is most apparent by the impact of AIDS on many African countries. According to projections made by the United Nations in 2002, the life expectancy at birth for 2010–2015 (if HIV/AIDS did not exist) would have been:{{cite book|url=https://www.un.org/ESA/population/publications/wpp2002/WPP2002-HIGHLIGHTSrev1.PDFUN|title=World Population Prospects – The 2002 Revision|volume=I: Comprehensive Tables|publisher=United Nations Secretariat, Department of Economic and Social Affairs, Population Division|date=2003|page=24|access-date=15 December 2020|archive-date=7 May 2022|archive-url=https://web.archive.org/web/20220507023722/https://www.un.org/ESA/population/publications/wpp2002/WPP2002-HIGHLIGHTSrev1.PDFUN|url-status=dead}}

• 70.7 years instead of 31.6 years, Botswana
• 69.9 years instead of 41.5 years, South Africa
• 70.5 years instead of 31.8 years, Zimbabwe

On average, eastern Europeans tend to live shorter lives than their western counterparts. For example, Spaniards from Madrid can expect to live to 85, but Bulgarians from the region of Severozapaden are predicted to live just past their 73rd birthday. This is in large part due to poor health habits, such as heavy smoking and high alcoholism in the region, and environmental factors, such as high air pollution.{{cite news|title=Why life expectancy is lower in eastern Europe|date=20 September 2018|url=https://www.economist.com/europe/2018/09/20/why-life-expectancy-is-lower-in-eastern-europe|url-access=subscription|access-date=2024-06-03|newspaper=The Economist|issn=0013-0613|url-status=live|archive-url=https://web.archive.org/web/20230731164643/https://www.economist.com/europe/2018/09/20/why-life-expectancy-is-lower-in-eastern-europe|archive-date=2023-07-31}}

File:Life expectancy post-COVID.pngIn 2022, the life expectancy was 77.5 in the United States, a decline from 2014, but an increase from 2021. In what has been described as a "life expectancy crisis", there were a total of 13 million "missing Americans" from 1980 to 2021, deaths that would have been averted if it had the standard mortality rate of "wealthy nations".{{citation needed|date=November 2024}}

The annual number of "missing Americans" has been increasing, with 622,534 in 2019 alone.{{cite web|title=The Missing Americans: Unprecedented US Mortality Far Exceeds Other Wealthy Nations|url=https://www.bu.edu/sph/news/articles/2023/the-missing-americans-unprecedented-us-mortality-far-exceeds-other-wealthy-nations/|access-date=2024-06-03|publisher=Boston University|department=School of Public Health|language=en|date=14 July 2023|first1=Jillian|last1=McKoy}} Most excess deaths in the United States can largely be attributed to increasing obesity, alcoholism, drug overdoses, car accidents, suicides, and murders, with poor sleep, unhealthy diets, and loneliness being linked to most of them.{{cite web|vauthors=Berg S|date=2023-03-10|title=What doctors wish patients knew about falling U.S. life expectancy|url=https://www.ama-assn.org/delivering-care/public-health/what-doctors-wish-patients-knew-about-falling-us-life-expectancy|access-date=2024-06-03|publisher=American Medical Association|language=en}}

Black Americans have generally shorter life expectancies than their White American counterparts. For example, white Americans in 2010 are expected to live until age 78.9, but black Americans only until age 75.1. This 3.8-year gap, however, is the lowest it has been since 1975 at the latest, the greatest difference being 7.1 years in 1993.{{cite journal|vauthors=Murphy SL, Xu JQ, Kochanek KD, Curtin SC, Arias E|title=Deaths: Final Data for 2010|journal=National Vital Statistics Reports|volume=61|issue=4|location=Hyattsville, MD|publisher=National Center for Health Statistics=|date=2013|pages=1–117|pmid=24979972|url=https://www.cdc.gov/nchs/data/nvsr/nvsr61/nvsr61_04.pdf}} In contrast, Asian American women live the longest of all ethnic and gender groups in the United States, with a life expectancy of 85.8 years.{{cite web|publisher=United States Department of Health and Human Services, Office of Minority Health|url=http://minorityhealth.hhs.gov/templates/browse.aspx?lvl=2&lvlID=53|title=Asian American/Pacific Islander Profile|archive-url=https://web.archive.org/web/20120204024943/http://minorityhealth.hhs.gov/templates/browse.aspx?lvl=2&lvlid=53|archive-date=4 February 2012}} The life expectancy of Hispanic Americans is 81.2 years.

In 2023, the life expectancy was 84.5 in Japan, 4.2 years above the OECD average, and one of the highest in the world. Japan's high life expectancy can largely be explained by their healthy diets, which are low on salt, fat, and red meat. For these reasons, Japan has a low obesity rate, and ultimately low mortality from heart disease and cancers.{{cite journal|vauthors=Tsugane S|title=Why has Japan become the world's most long-lived country: insights from a food and nutrition perspective|journal=European Journal of Clinical Nutrition|volume=75|issue=6|pages=921–928|date=June 2021|pmid=32661353|pmc=8189904|doi=10.1038/s41430-020-0677-5}}

Cities also experience a wide range of life expectancy based on neighborhood breakdowns. This is largely due to economic clustering and poverty conditions that tend to associate based on geographic location. Multi-generational poverty found in struggling neighborhoods also contributes. In American cities such as Cincinnati, the life expectancy gap between low income and high-income neighborhoods touches 20 years.{{cite web|url=http://waterfieldsllc.com/about-waterfields/social-mission/root-causes-poverty/|archive-url=https://web.archive.org/web/20150906041120/http://waterfieldsllc.com/about-waterfields/social-mission/root-causes-poverty/|archive-date=6 September 2015|title=The Root Causes of Poverty|publisher=Waterfields, LLC|location=Cincinnati, Ohio|access-date=2015-03-04}}

{{See also|Preston curve}}

File:Life expectancy vs healthcare spending.jpg.{{cite journal|url=https://ourworldindata.org/the-link-between-life-expectancy-and-health-spending-us-focus|title=Link between health spending and life expectancy: US is an outlier|date=26 May 2017|vauthors=Roser M|author-link1=Max Roser|journal=Our World in Data}} Click the sources tab under the chart for info on the countries, healthcare expenditures, and data sources. See the later version of the chart [https://ourworldindata.org/us-life-expectancy-low here].]]

Economic circumstances also affect life expectancy. For example, in the United Kingdom, life expectancy in the wealthiest and richest areas is several years higher than in the poorest areas. This may reflect factors such as diet and lifestyle, as well as access to medical care. It may also reflect a selective effect: people with chronic life-threatening illnesses are less likely to become wealthy or to reside in affluent areas.{{cite web|publisher=Department of Health|location=UK|url=http://www.dh.gov.uk/PublicationsAndStatistics/Publications/PublicationsPolicyAndGuidance/PublicationsPolicyAndGuidanceArticle/fs/en?CONTENT_ID=4117696&chk=OXFbWI|title=Tackling health inequalities: Status report on the Programme for Action|archive-url=https://web.archive.org/web/20070205110912/http://www.dh.gov.uk/PublicationsAndStatistics/Publications/PublicationsPolicyAndGuidance/PublicationsPolicyAndGuidanceArticle/fs/en?CONTENT_ID=4117696&chk=OXFbWI|archive-date=5 February 2007}} In Glasgow, the disparity is amongst the highest in the world: life expectancy for males in the heavily deprived Calton area stands at 54, which is 28 years less than in the affluent area of Lenzie, which is only {{Convert|8|km|mi|abbr=on}} away.{{cite news|url=http://news.bbc.co.uk/1/hi/health/7584056.stm#Life%20expectancy|title=Social factors key to ill health|date=28 August 2008|publisher=BBC News|access-date=28 August 2008}}{{cite news|url=http://news.bbc.co.uk/1/hi/scotland/glasgow_and_west/7584450.stm|title=GP explains life expectancy gap|date=28 August 2008|publisher=BBC News|access-date=28 August 2008}}

A 2013 study found a pronounced relationship between economic inequality and life expectancy.{{cite news|vauthors=Fletcher MA|title=Research ties economic inequality to gap in life expectancy|url=https://www.washingtonpost.com/business/economy/research-ties-economic-inequality-to-gap-in-life-expectancy/2013/03/10/c7a323c4-7094-11e2-8b8d-e0b59a1b8e2a_story.html|access-date=23 March 2013|newspaper=The Washington Post|date=10 March 2013}} However, in contrast, a study by José A. Tapia Granados and Ana Diez Roux at the University of Michigan found that life expectancy actually increased during the Great Depression, and during recessions and depressions in general.{{cite web|publisher=University of Michigan|work=ScienceDaily|url=https://www.sciencedaily.com/releases/2009/09/090928172530.htm|title=Did The Great Depression Have A Silver Lining? Life Expectancy Increased By 6.2 Years|date=29 September 2009|access-date=3 April 2011}} The authors suggest that when people are working at a more extreme degree during prosperous economic times, they undergo more stress, exposure to pollution, and the likelihood of injury among other longevity-limiting factors.

Life expectancy is also likely to be affected by exposure to high levels of highway air pollution or industrial air pollution. This is one way that occupation can have a major effect on life expectancy. Coal miners (and in prior generations, asbestos cutters) often have lower life expectancies than average. Other factors affecting an individual's life expectancy are genetic disorders, drug use, tobacco smoking, excessive alcohol consumption, obesity, access to health care, diet, and exercise.

File:Healthy life expectancy bar chart -world -sex.png

File:LifeExpectancyBetweenFemaleAndMales.jpg. (2015){{cite web|url=http://smart-unit-converter.com/life-expectancy.php|title=How long will I live? Estimate remaining life expectancy for all countries in the world|vauthors=Pele L}}]]

File:Comparison of male and female life expectancy -world.svg for 2019. Open the original [https://upload.wikimedia.org/wikipedia/commons/b/b3/Comparison_of_male_and_female_life_expectancy_-world.svg svg-file] and hover over a bubble to show its data. The square of the bubbles is proportional to country population based on estimation of the UN.]]

In the present, female human life expectancy is greater than that of males, despite females having higher morbidity rates (see health survival paradox). There are many potential reasons for this. Traditional arguments tend to favor sociology-environmental factors: historically, men have generally consumed more tobacco, alcohol, and drugs than women in most societies, and are more likely to die from many associated diseases such as lung cancer, tuberculosis, and cirrhosis of the liver. Men are also more likely to die from injuries, whether unintentional (such as occupational, war, or car wrecks) or intentional (suicide).{{cite web|publisher=World Health Organization|year=2004|work=The world health report 2004 – changing history|title=Annex Table 2: Deaths by cause, sex and mortality stratum in WHO regions, estimates for 2002|url=https://www.who.int/entity/whr/2004/annex/topic/en/annex_2_en.pdf|access-date=1 November 2008}} Men are also more likely to die from most of the leading causes of death (some already stated above) than women. Some of these in the United States include cancer of the respiratory system, motor vehicle accidents, suicide, cirrhosis of the liver, emphysema, prostate cancer, and coronary heart disease. These far outweigh the female mortality rate from breast cancer and cervical cancer. In the past, mortality rates for females in child-bearing age groups were higher than for males at the same age.

A paper from 2015 found that female foetuses have a higher mortality rate than male foetuses.{{cite journal|vauthors=Orzack SH, Stubblefield JW, Akmaev VR, Colls P, Munné S, Scholl T, Steinsaltz D, Zuckerman JE|title=The human sex ratio from conception to birth|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=112|issue=16|pages=E2102–11|date=April 2015|pmid=25825766|pmc=4413259|doi=10.1073/pnas.1416546112|doi-access=free|bibcode=2015PNAS..112E2102O}} This finding contradicts papers dating from 2002 and earlier that attribute the male sex to higher in-utero mortality rates.{{cite journal|vauthors=Kalben BB|title=Why men die younger: causes of mortality differences by sex.|journal=North American Actuarial Journal|date=October 2000|volume=4|issue=4|pages=83–111|doi=10.1080/10920277.2000.10595939|url=http://www.soa.org/library/monographs/life/why-men-die-younger-causes-of-mortality-differences-by-sex/2001/january/m-li01-1-05.pdf|access-date=31 October 2011|archive-date=13 September 2017|archive-url=https://web.archive.org/web/20170913135329/http://www.soa.org/library/monographs/life/why-men-die-younger-causes-of-mortality-differences-by-sex/2001/january/m-li01-1-05.pdf|url-status=dead}}{{cite journal|vauthors=Naeye RL, Burt LS, Wright DL, Blanc WA, Tatter D|title=Neonatal mortality, the male disadvantage|journal=Pediatrics|volume=48|issue=6|pages=902–906|date=December 1971|pmid=5129451|doi=10.1542/peds.48.6.902}}{{cite journal|vauthors=Waldron I|title=Sex differences in human mortality: the role of genetic factors|journal=Social Science & Medicine|volume=17|issue=6|pages=321–333|date=1983-01-01|pmid=6344225|doi=10.1016/0277-9536(83)90234-4|author-link1=Ingrid Waldron}} Among the smallest premature babies (those under {{Convert|2|lb|g|abbr=none}}), females have a higher survival rate. At the other extreme, about 90% of individuals aged 110 are female. The difference in life expectancy between men and women in the United States dropped from 7.8 years in 1979 to 5.3 years in 2005, with women expected to live to age 80.1 in 2005.{{cite web|vauthors=Hitti M|title=U.S. Life Expectancy Best Ever, Says CDC|work=eMedicine|publisher=WebMD|date=28 February 2005|url=http://www.webmd.com/healthy-aging/news/20050228/us-life-expectancy-best-ever-says-cdc|access-date=18 January 2011}} Data from the United Kingdom shows the gap in life expectancy between men and women decreasing in later life. This may be attributable to the effects of infant mortality and young adult death rates.{{cite web|title=Life expectancy—care quality indicators|url=http://www.qualitywatch.org.uk/indicator/life-expectancy#vis-ref_221|website=QualityWatch|publisher=Nuffield Trust & Health Foundation|access-date=16 April 2015}}

Some argue that shorter male life expectancy is merely another manifestation of the general rule, seen in all mammal species, that larger-sized individuals within a species tend, on average, to have shorter lives.{{cite web|vauthors=Stindl R|url=http://jerrymondo.tripod.com/lgev/id1.html|title=Telemores, sexual size dimorphism and gender gap in life expectancy|publisher=Jerrymondo.tripod.com|access-date=4 November 2010}}{{cite journal|vauthors=Samaras TT, Heigh GH|title=How human size affects longevity and mortality from degenerative diseases|journal=Townsend Letter for Doctors & Patients|volume=159|issue=78–85|pages=133–139}} This biological difference{{clarify|date=September 2022}} occurs because women have more resistance to infections and degenerative diseases.

In her extensive review of the existing literature, Kalben concluded that the fact that women live longer than men was observed at least as far back as 1750 and that, with relatively equal treatment, today males in all parts of the world experience greater mortality than females. However, Kalben's study was restricted to data in Western Europe alone, where the demographic transition occurred relatively early. United Nations statistics from mid-twentieth century onward, show that in all parts of the world, females have a higher life expectancy at age 60 than males.{{cite web|work=Department of Economic and Social Affairs|page=53|title=World Population Ageing 2015 (ST/ESA/SER.A/390)|url=https://www.un.org/en/development/desa/population/publications/pdf/ageing/WPA2015_Report.pdf|publisher=United Nations|access-date=11 March 2021}} Of 72 selected causes of death, only 6 yielded greater female than male age-adjusted death rates in 1998 in the United States. Except for birds, for almost all of the animal species studied, males have higher mortality than females. Evidence suggests that the sex mortality differential in people is due to both biological/genetic and environmental/behavioral risk and protective factors.

One recent suggestion is that mitochondrial mutations which shorten lifespan continue to be expressed in males (but less so in females) because mitochondria are inherited only through the mother. By contrast, natural selection weeds out mitochondria that reduce female survival; therefore, such mitochondria are less likely to be passed on to the next generation. This thus suggests that females tend to live longer than males. The authors claim that this is a partial explanation.{{cite news|url=https://www.bbc.co.uk/news/health-19093442|title=Fruit flies offer DNA clue to why women live longer|publisher=BBC News|date=2 August 2012}}{{cite web|vauthors=Myers PZ|author-link1=PZ Myers|date=6 February 2013|url=http://scienceblogs.com/pharyngula/2013/02/06/mothers-curse/|title=Mother's Curse}}

Another explanation is the unguarded X hypothesis. According to this hypothesis, one reason for why the average lifespan of males is not as long as that of females––by 18% on average, according to the study––is that they have a Y chromosome which cannot protect an individual from harmful genes expressed on the X chromosome, while a duplicate X chromosome, as present in female organisms, can ensure harmful genes are not expressed.{{cite news|vauthors=Gilbert L|date=4 March 2020|title=Why men (and other male animals) die younger: It's all in the Y chromosome|url=https://phys.org/news/2020-03-men-male-animals-die-younger.html|access-date=5 April 2020|work=phys.org}}{{cite journal|vauthors=Xirocostas ZA, Everingham SE, Moles AT|title=The sex with the reduced sex chromosome dies earlier: a comparison across the tree of life|journal=Biology Letters|volume=16|issue=3|pages=20190867|date=March 2020|pmid=32126186|pmc=7115182|doi=10.1098/rsbl.2019.0867|doi-access=free}}

In developed countries, starting around 1880, death rates decreased faster among women, leading to differences in mortality rates between males and females. Before 1880, death rates were the same. In people born after 1900, the death rate of 50- to 70-year-old men was double that of women of the same age. Men may be more vulnerable to cardiovascular disease than women, but this susceptibility was evident only after deaths from other causes, such as infections, started to decline.{{cite web|vauthors=Rettner R|title=When Did Women Start to Outlive Men?|website=Live Science|date=6 July 2015|url=http://www.livescience.com/51455-women-outlive-men.html|access-date=2015-07-08}} Most of the difference in life expectancy between the sexes is accounted for by differences in the rate of death by cardiovascular diseases among persons aged 50–70.{{cite journal|vauthors=Beltrán-Sánchez H, Finch CE, Crimmins EM|title=Twentieth century surge of excess adult male mortality|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=112|issue=29|pages=8993–8|date=July 2015|pmid=26150507|pmc=4517277|doi=10.1073/pnas.1421942112|doi-access=free|bibcode=2015PNAS..112.8993B}}

{{Further|Genetics of aging}}

The heritability of lifespan is estimated to be less than 10%, meaning the majority of variation in lifespan is attributable due to differences in environment rather than genetic variation.{{cite journal|vauthors=Ruby JG, Wright KM, Rand KA, Kermany A, Noto K, Curtis D, Varner N, Garrigan D, Slinkov D, Dorfman I, Granka JM, Byrnes J, Myres N, Ball C|title=Estimates of the Heritability of Human Longevity Are Substantially Inflated due to Assortative Mating|journal=Genetics|volume=210|issue=3|pages=1109–1124|date=November 2018|pmid=30401766|pmc=6218226|doi=10.1534/genetics.118.301613}} However, researchers have identified regions of the genome which can influence the length of life and the number of years lived in good health. For example, a genome-wide association study of 1 million lifespans found 12 genetic loci which influenced lifespan by modifying susceptibility to cardiovascular and smoking-related disease.{{cite journal|vauthors=Timmers PR, Mounier N, Lall K, Fischer K, Ning Z, Feng X, Bretherick AD, Clark DW, Shen X, Esko T, Kutalik Z, Wilson JF, Joshi PK|title=Genomics of 1 million parent lifespans implicates novel pathways and common diseases and distinguishes survival chances|journal=eLife|volume=8|issue=e39856|date=January 2019|pmid=30642433|pmc=6333444|doi=10.7554/eLife.39856|doi-access=free}} The locus with the largest effect is APOE. Carriers of the APOE ε4 allele live approximately one year less than average (per copy of the ε4 allele), mainly due to increased risk of Alzheimer's disease.

File:Healthspan, parental lifespan, and longevity are highly genetically correlated.webp

In July 2020, scientists identified 10 genomic loci with consistent effects across multiple lifespan-related traits, including healthspan, lifespan, and longevity.{{cite journal|vauthors=Timmers PR, Wilson JF, Joshi PK, Deelen J|title=Multivariate genomic scan implicates novel loci and haem metabolism in human ageing|journal=Nature Communications|volume=11|issue=1|pages=3570|date=July 2020|pmid=32678081|pmc=7366647|doi=10.1038/s41467-020-17312-3|bibcode=2020NatCo..11.3570T|doi-access=free}} The genes affected by variation in these loci highlighted haem metabolism as a promising candidate for further research within the field. This study suggests that high levels of iron in the blood likely reduce, and genes involved in metabolising iron likely increase healthy years of life in humans.{{cite news|author=University of Edinburgh|date=20 July 2020|title=Blood iron levels could be key to slowing ageing, gene study shows|url=https://phys.org/news/2020-07-blood-iron-key-ageing-gene.html|access-date=18 August 2020|work=phys.org}}

A follow-up study which investigated the genetics of frailty and self-rated health in addition to healthspan, lifespan, and longevity also highlighted haem metabolism as an important pathway, and found genetic variants which lower blood protein levels of LPA and VCAM1 were associated with increased healthy lifespan.{{cite journal|vauthors=Timmers PR, Tiys ES, Sakaue S, Akiyama M, Kiiskinen TT, Zhou W, Hwang SJ, Yao C, Deelen J, Levy D, Ganna A, Kamatani Y, Okada Y, Joshi PK, Wilson JF, Tsepilov YA|title=Mendelian randomization of genetically independent aging phenotypes identifies LPA and VCAM1 as biological targets for human aging|journal=Nature Aging|volume=2|issue=1|pages=19–30|date=January 2022|pmid=37118362|doi=10.1038/s43587-021-00159-8|hdl-access=free|s2cid=246093885|doi-access=free|hdl=20.500.11820/1bac547c-2eb9-47e1-b4b8-e80d741941c7}}

{{Main|Centenarian}}

In developed countries, the number of centenarians is increasing at approximately 5.5% per year, which means doubling the centenarian population every 13 years, pushing it from some 455,000 in 2009 to 4.1 million in 2050.United Nations [https://healthprep.com/aging/#WPA2009-report.pdf "World Population Ageing 2009"]; ST/ESA/SER.A/295, Population Division, Department of Economic and Social Affairs, United Nations, New York, October 2010, liv + 73 pp. Japan is the country with the highest ratio of centenarians (347 for every 1 million inhabitants in September 2010). Shimane Prefecture had an estimated 743 centenarians per million inhabitants.{{cite web|work=The Japan Times|url=http://search.japantimes.co.jp/cgi-bin/nn20100915a8.html|title=Centenarians to Hit Record 44,000|date=15 September 2010}} Okinawa 667 centenarians per 1 million inhabitants in September 2010, had been for a long time the Japanese prefecture with the largest ratio of centenarians, partly because it also had the largest loss of young and middle-aged population during the Pacific War.

In the United States, the number of centenarians grew from 32,194 in 1980 to 71,944 in November 2010 (232 centenarians per million inhabitants).{{cite web|url=https://www.census.gov/popest/national/asrh/2009-nat-res.html|title=Resident Population. National Population Estimates for the 2000s. Monthly Postcensal Resident Population, by single year of age, sex, race, and Hispanic Origin|archive-url=https://web.archive.org/web/20131010072957/http://www.census.gov/popest/national/asrh/2009-nat-res.html|archive-date=10 October 2013|work=Bureau of the Census}} Different figures, based on earlier assumptions (104,754 centenarians on Nov.1, 2009) are provided in {{cite web|url=https://www.census.gov/newsroom/releases/pdf/cb10-ff06.pdf|title=Older Americans Month|date=May 2010|archive-url=https://web.archive.org/web/20160216221613/http://www.census.gov/newsroom/releases/pdf/cb10-ff06.pdf|archive-date=16 February 2016|publisher=Bureau of the Census|work=Facts for Features|page=5}}

Mental illness is reported to occur in approximately 18% of the average American population.{{cite web|vauthors=Bekiempis V|url=http://www.newsweek.com/nearly-1-5-americans-suffer-mental-illness-each-year-230608|title=Nearly 1 in 5 Americans Suffers From Mental Illness Each Year|website=Newsweek|date=28 February 2014}}{{cite journal|vauthors=Steel Z, Marnane C, Iranpour C, Chey T, Jackson JW, Patel V, Silove D|title=The global prevalence of common mental disorders: a systematic review and meta-analysis 1980–2013|journal=International Journal of Epidemiology|volume=43|issue=2|pages=476–493|date=April 2014|pmid=24648481|pmc=3997379|doi=10.1093/ije/dyu038}}

File: Smi graph by Mark.png

The mentally ill have been shown to have a 10- to 25-year reduction in life expectancy.{{cite news|url=https://mobile.nytimes.com/2018/05/30/upshot/mental-illness-health-disparity-longevity.html|title=The Largest Health Disparity We Don't Talk About|newspaper=The New York Times|date=2018-05-30|vauthors=Khullar D}} Generally, the reduction of lifespan in the mentally ill population compared to the mentally stable population has been studied and documented.{{cite journal|vauthors=Wahlbeck K, Westman J, Nordentoft M, Gissler M, Laursen TM|title=Outcomes of Nordic mental health systems: life expectancy of patients with mental disorders|journal=The British Journal of Psychiatry|volume=199|issue=6|pages=453–458|date=December 2011|pmid=21593516|doi=10.1192/bjp.bp.110.085100|doi-access=free}}{{cite journal|vauthors=Reininghaus U, Dutta R, Dazzan P, Doody GA, Fearon P, Lappin J, Heslin M, Onyejiaka A, Donoghue K, Lomas B, Kirkbride JB, Murray RM, Croudace T, Morgan C, Jones PB|title=Mortality in schizophrenia and other psychoses: a 10-year follow-up of the ӔSOP first-episode cohort|journal=Schizophrenia Bulletin|volume=41|issue=3|pages=664–673|date=May 2015|pmid=25262443|pmc=4393685|doi=10.1093/schbul/sbu138}}{{cite journal|vauthors=Laursen TM, Munk-Olsen T, Vestergaard M|title=Life expectancy and cardiovascular mortality in persons with schizophrenia|journal=Current Opinion in Psychiatry|volume=25|issue=2|pages=83–88|date=March 2012|pmid=22249081|doi=10.1097/YCO.0b013e32835035ca|s2cid=13646442}}{{cite web|url=http://www.medscape.com/viewarticle/861159|title=Antipsychotics Linked to Mortality in Parkinson's|website=Medscape|access-date=9 April 2018}}{{cite journal|vauthors=Rosenbaum L|title=Closing the Mortality Gap – Mental Illness and Medical Care|journal=The New England Journal of Medicine|volume=375|issue=16|pages=1585–1589|date=October 2016|pmid=27797313|doi=10.1056/NEJMms1610125}}

The greater mortality of people with mental disorders may be due to death from injury, from co-morbid conditions, or medication side effects.{{cite web|url=http://www.northamptonchron.co.uk/news/inquest-told-there-was-a-lost-opportunity-to-treat-mental-health-patient-who-died-following-severe-constipation-1-5244246|title=Inquest told there was a "lost opportunity" to treat mental health patient who died following severe constipation|access-date=25 July 2017|archive-date=9 April 2019|archive-url=https://web.archive.org/web/20190409015423/https://www.northamptonchron.co.uk/news/inquest-told-there-was-a-lost-opportunity-to-treat-mental-health-patient-who-died-following-severe-constipation-1-5244246|url-status=dead}} For instance, psychiatric medications can increase the risk of developing diabetes.{{cite journal|vauthors=Kumar PN, Thomas B|title=Hyperglycemia associated with olanzapine treatment|journal=Indian Journal of Psychiatry|volume=53|issue=2|pages=176–177|date=April 2011|pmid=21772658|pmc=3136028|doi=10.4103/0019-5545.82562|doi-access=free}}{{cite news|url=https://www.nytimes.com/2007/10/06/business/06zyprexa.html|title=Lilly Adds Strong Warning Label to Zyprexa, a Schizophrenia Drug|date=6 October 2007|work=The New York Times|access-date=9 April 2018}}{{cite book|url=https://books.google.com/books?id=0RDZdDW0EqEC&q=zyprexa%20increase%20the%20chance%20of%20developing%20the%20disease%20of%20diabetes&pg=PA17|title=Type 2 Diabetes, Pre-Diabetes, and the Metabolic Syndrome|vauthors=Codario RA|date=28 October 2007|publisher=Springer Science & Business Media|isbn=978-1-59259-932-5}}{{cite web|url=http://www.medscape.com/viewarticle/863871|title=Antipsychotic-Related Metabolic Testing Falls Far Short|publisher=MedScape|access-date=9 April 2018}} It has been shown that the psychiatric medication olanzapine can increase risk of developing agranulocytosis, among other comorbidities.{{cite journal|vauthors=Alvir JM, Lieberman JA, Safferman AZ, Schwimmer JL, Schaaf JA|title=Clozapine-induced agranulocytosis. Incidence and risk factors in the United States|journal=The New England Journal of Medicine|volume=329|issue=3|pages=162–167|date=July 1993|pmid=8515788|doi=10.1056/NEJM199307153290303|doi-access=free}}{{cite web|url=https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/020592s057,021086s036,021253s045lbl.pdf|title=Zyprexa Prescribing Information|date=2010|website=U.S. Food Drug and Administration}} Psychiatric medicines also affect the gastrointestinal tract; the mentally ill have a four times risk of gastrointestinal disease.{{cite journal|vauthors=Philpott HL, Nandurkar S, Lubel J, Gibson PR|title=Drug-induced gastrointestinal disorders|journal=Frontline Gastroenterology|volume=5|issue=1|pages=49–57|date=January 2014|pmid=28839751|pmc=5369702|doi=10.1136/flgastro-2013-100316}}{{cite journal|vauthors=Rege S, Lafferty T|title=Life-threatening constipation associated with clozapine|journal=Australasian Psychiatry|volume=16|issue=3|pages=216–219|date=June 2008|pmid=18568631|doi=10.1080/10398560701882203|s2cid=32093594}}{{cite journal|vauthors=Hibbard KR, Propst A, Frank DE, Wyse J|title=Fatalities associated with clozapine-related constipation and bowel obstruction: a literature review and two case reports|journal=Psychosomatics|volume=50|issue=4|pages=416–419|year=2009|pmid=19687183|doi=10.1176/appi.psy.50.4.416|doi-access=free}}

As of 2020 and the COVID-19 pandemic, researchers have found an increased risk of death in the mentally ill.{{cite journal|vauthors=Nemani K, Li C, Olfson M, Blessing EM, Razavian N, Chen J, Petkova E, Goff DC|title=Association of Psychiatric Disorders With Mortality Among Patients With COVID-19|journal=JAMA Psychiatry|volume=78|issue=4|pages=380–386|date=April 2021|pmid=33502436|pmc=7841576|doi=10.1001/jamapsychiatry.2020.4442}}{{cite journal|vauthors=Wang Q, Xu R, Volkow ND|title=Increased risk of COVID-19 infection and mortality in people with mental disorders: analysis from electronic health records in the United States|journal=World Psychiatry|volume=20|issue=1|pages=124–130|date=February 2021|pmid=33026219|pmc=7675495|doi=10.1002/wps.20806}}{{cite journal|vauthors=Li L, Li F, Fortunati F, Krystal JH|title=Association of a Prior Psychiatric Diagnosis With Mortality Among Hospitalized Patients With Coronavirus Disease 2019 (COVID-19) Infection|journal=JAMA Network Open|volume=3|issue=9|pages=e2023282|date=September 2020|pmid=32997123|pmc=7527869|doi=10.1001/jamanetworkopen.2020.23282}}

The life expectancy of people with diabetes, which is 9.3% of the U.S. population, is reduced by roughly 10–20 years.{{cite web|url=http://www.diabetes.co.uk/diabetes-life-expectancy.html|title=Diabetes Life Expectancy – Type 1 and Type 2 Life Expectancy|date=15 January 2019}}[https://www.cdc.gov/features/diabetesfactsheet/ Centers for Disease Control and Prevention] People over 60 years old with Alzheimer's disease have about a 50% life expectancy of 3–10 years.{{cite journal|vauthors=Zanetti O, Solerte SB, Cantoni F|title=Life expectancy in Alzheimer's disease (AD)|journal=Archives of Gerontology and Geriatrics|volume=49|issue=Suppl 1|pages=237–243|date=2009|pmid=19836639|doi=10.1016/j.archger.2009.09.035}} Other demographics that tend to have a lower life expectancy than average include transplant recipients{{cite journal|vauthors=Kiberd BA, Keough-Ryan T, Clase CM|title=Screening for prostate, breast and colorectal cancer in renal transplant recipients|journal=American Journal of Transplantation|volume=3|issue=5|pages=619–625|date=May 2003|pmid=12752319|doi=10.1034/j.1600-6143.2003.00118.x|s2cid=20247054|doi-access=free}} and the obese.{{cite journal|vauthors=Diehr P, O'Meara ES, Fitzpatrick A, Newman AB, Kuller L, Burke G|title=Weight, mortality, years of healthy life, and active life expectancy in older adults|journal=Journal of the American Geriatrics Society|volume=56|issue=1|pages=76–83|date=January 2008|pmid=18031486|pmc=3865852|doi=10.1111/j.1532-5415.2007.01500.x|author-link=Paula Diehr}}

Education on all levels has been shown to be strongly associated with increased life expectancy.{{cite journal|vauthors=Hummer RA, Hernandez EM|title=The Effect of Educational Attainment on Adult Mortality in the United States|journal=Population Bulletin|volume=68|issue=1|pages=1–16|date=June 2013|pmid=25995521|pmc=4435622}} This association may be due partly to higher income,{{cite web|url=https://www.bls.gov/careeroutlook/2018/data-on-display/education-pays.htm|title=Measuring the value of education : Career Outlook: U.S. Bureau of Labor Statistics|vauthors=Torpey E|website=bls.gov|access-date=2019-03-10}} which can lead to increased life expectancy. Despite the association, among identical twin pairs with different education levels, there is only weak evidence of a relationship between educational attainment and adult mortality.

According to a paper from 2015, the mortality rate for the Caucasian population in the United States from 1993 to 2001 is four times higher{{dubious|date=September 2022}} for those who did not complete high school compared to those who have at least 16 years of education. In fact, within the U.S. adult population, people with less than a high school education have the shortest life expectancies.

Preschool education also plays a large role in life expectancy. It was found that high-quality early-stage childhood education had positive effects on health. Researchers discovered this by analyzing the results of the Carolina Abecedarian Project, finding that the disadvantaged children who were randomly assigned to treatment had lower instances of risk factors for cardiovascular and metabolic diseases in their mid-30s.{{cite journal|vauthors=Campbell F, Conti G, Heckman JJ, Moon SH, Pinto R, Pungello E, Pan Y|title=Early childhood investments substantially boost adult health|journal=Science|location=New York, N.Y.|volume=343|issue=6178|pages=1478–85|date=March 2014|pmid=24675955|pmc=4028126|doi=10.1126/science.1248429|bibcode=2014Sci...343.1478C}}

{{Main|Life history theory}}

Various species of plants and animals, including humans, have different lifespans. Evolutionary theory states that organisms which—by virtue of their defenses or lifestyle—live for long periods and avoid accidents, disease, predation, etc. are likely to have genes that code for slow aging, which often translates to good cellular repair. One theory is that if predation or accidental deaths prevent most individuals from living to an old age, there will be less natural selection to increase the intrinsic life span.{{cite journal|vauthors=Williams G|title=Pleiotropy, natural selection, and the evolution of senescence|journal=Evolution|volume=11|pages=398–411|year=1957|doi=10.2307/2406060|issue=4|publisher=Society for the Study of Evolution|jstor=2406060}} That finding was supported in a classic study of opossums by Austad;{{cite journal|vauthors=Austad SN|title=Retarded senescence in an insular population of Virginia opossums|journal=J. Zool. Lond.|volume=229|issue=4|pages=695–708|year=1993|doi=10.1111/j.1469-7998.1993.tb02665.x}} however, the opposite relationship was found in an equally prominent study of guppies by Reznick.{{cite journal|vauthors=Reznick DN, Bryant MJ, Roff D, Ghalambor CK, Ghalambor DE|title=Effect of extrinsic mortality on the evolution of senescence in guppies|journal=Nature|volume=431|issue=7012|pages=1095–1099|date=October 2004|pmid=15510147|doi=10.1038/nature02936|s2cid=205210169|bibcode=2004Natur.431.1095R}}{{cite journal|vauthors=Mitteldorf J, Pepper JW|title=How can evolutionary theory accommodate recent empirical results on organismal senescence?|journal=Theory in Biosciences = Theorie in den Biowissenschaften|volume=126|issue=1|pages=3–8|date=August 2007|pmid=18087751|doi=10.1007/s12064-007-0001-0|s2cid=7305206}}

One prominent and very popular theory states that lifespan can be lengthened by a tight budget for food energy called caloric restriction.{{cite journal|vauthors=Kirkwood TB|title=Evolution of ageing|journal=Nature|volume=270|issue=5635|pages=301–304|date=November 1977|pmid=593350|doi=10.1038/270301a0|s2cid=492012|bibcode=1977Natur.270..301K}} Caloric restriction observed in many animals (most notably mice and rats) shows a near doubling of life span from a very limited calorific intake. Support for the theory has been bolstered by several new studies linking lower basal metabolic rate to increased life expectancy.{{cite journal|vauthors=Hulbert AJ, Pamplona R, Buffenstein R, Buttemer WA|title=Life and death: metabolic rate, membrane composition, and life span of animals|journal=Physiological Reviews|volume=87|issue=4|pages=1175–1213|date=October 2007|pmid=17928583|doi=10.1152/physrev.00047.2006|url=http://pdfs.semanticscholar.org/0c1b/ece43845df356bc2dda22dd27a82a8ef95e8.pdf|url-status=dead|s2cid=11903260|archive-url=https://web.archive.org/web/20190218133041/http://pdfs.semanticscholar.org/0c1b/ece43845df356bc2dda22dd27a82a8ef95e8.pdf|archive-date=18 February 2019}}{{cite journal|vauthors=Olshansky SJ, Rattan SI|title=What determines longevity: Metabolic rate or stability?|journal=Discovery Medicine|volume=5|issue=28|pages=359–362|date=August 2005|pmid=20704872|url=http://www.discoverymedicine.com/S-J-Olshansky/2009/07/25/what-determines-longevity-metabolic-rate-or-stability}}{{cite journal|vauthors=Aguilaniu H, Durieux J, Dillin A|title=Metabolism, ubiquinone synthesis, and longevity|journal=Genes & Development|volume=19|issue=20|pages=2399–2406|date=October 2005|pmid=16230529|doi=10.1101/gad.1366505|doi-access=free}} That is the key to why animals like giant tortoises can live so long.{{cite web|url=http://www.immortalhumans.com/the-longevity-secret-for-tortoises-is-held-in-their-low-metabolism-rate/|title=The Longevity Secret for Tortoises Is Held in Their Low Metabolism Rate|archive-url=https://web.archive.org/web/20131112164840/http://www.immortalhumans.com/the-longevity-secret-for-tortoises-is-held-in-their-low-metabolism-rate/|archive-date=12 November 2013|url-status=dead}} Studies of humans with life spans of at least 100 have shown a link to decreased thyroid activity, resulting in their lowered metabolic rate.{{No source|date=January 2023}}

The ability of skin fibroblasts to perform DNA repair after UV irradiation was measured in shrew, mouse, rat, hamster, cow, elephant and human.{{cite journal|vauthors=Hart RW, Setlow RB|title=Correlation between deoxyribonucleic acid excision-repair and life-span in a number of mammalian species|journal=Proceedings of the National Academy of Sciences of the United States of America|volume=71|issue=6|pages=2169–73|date=June 1974|pmid=4526202|pmc=388412|doi=10.1073/pnas.71.6.2169|doi-access=free|bibcode=1974PNAS...71.2169H}} It was found that DNA repair capability increased systematically with species life span. Since this original study in 1974, at least 14 additional studies were performed on mammals to test this correlation.{{cite book|vauthors=Bernstein C, Bernstein H|date=1991|title=Aging, Sex, and DNA Repair|publisher=Academic Press|location=San Diego, CA|pages=109–113}} In all, but two of these studies, lifespan correlated with DNA repair levels, suggesting that DNA repair capability contributes to life expectancy. See DNA damage theory of aging.

In a broad survey of zoo animals, no relationship was found between investment of the animal in reproduction and its life span.{{cite journal|vauthors=Ricklefs RE, Cadena CD|title=Lifespan is unrelated to investment in reproduction in populations of mammals and birds in captivity|journal=Ecology Letters|volume=10|issue=10|pages=867–872|date=October 2007|pmid=17845285|doi=10.1111/j.1461-0248.2007.01085.x|bibcode=2007EcolL..10..867R}}

{{further|Life table#The mathematics}}

File:Survivaltree.png

In actuarial notation, the probability of surviving from age $x$ to age $x+n$ is denoted $\backslash ,\_np\_x\backslash !$ and the probability of dying during age $x$ (i.e. between ages $x$ and $x+1$) is denoted $q\_x\backslash !$ . For example, if 10% of a group of people alive at their 90th birthday die before their 91st birthday, the age-specific death probability at 90 would be 10%. This probability describes the likelihood of dying at that age, and is not the rate at which people of that age die.{{efn| Note the different units: a probability is unit-less, whereas a mortality rate has units (such as deaths per population per year).}} It can be shown that{{NumBlk|:|$\{\}\_kp\_x\; \backslash ,\; q\_\{x+k\}\; =\; \{\}\_k\; p\_x\; -\; \{\}\_\{k+1\}p\_x$|{{EquationRef|1}}}}

The curtate future lifetime, denoted $K(x)$, is a discrete random variable representing the remaining lifetime at age $x$, rounded down to whole years. Life expectancy, more technically called the curtate expected lifetime and denoted $\backslash ,e\_x\backslash !$ ,{{efn|name=exsymbol}} is the mean of $K(x)$—that is to say, the expected number of whole years of life remaining, assuming survival to age $x$.{{cite web|vauthors=Kinney B|date=2019-05-01|title=Curtate Expectation of Life|url=https://infinityisreallybig.com/2019/05/01/curtate-expectation-of-life/|access-date=2022-11-18|website=Infinity is Really Big}} So,

{{NumBlk|:|$e\_x\; =\; \backslash operatorname\{E\}[K(x)]\; =\; \backslash sum\_\{k=0\}^\backslash infty\; k\backslash ,\; \backslash cdot\; \backslash Pr(K(x)=k)\; =\; \backslash sum\_\{k=0\}^\{\backslash infty\}k\backslash ,\; \backslash ,\_kp\_x\; \backslash ,\backslash ,\; q\_\{x+k\}$|{{EquationRef|2}}}}

Substituting ({{EquationNote|1}}) into the sum and simplifying gives the final result{{cite book|title=Models for Quantifying Risk|edition=Third|vauthors=Cunningham R, Herzog T, London R|publisher=Actex|year=2008|isbn=978-1-56698-676-2}} page 92.

{{NumBlk|:|$e\_x\; =\; \backslash sum\_\{k=1\}^\backslash infty\; \{\}\; \backslash ,\; \backslash ,\backslash ,\; \_k\; p\_x$|{{EquationRef|3}}}}

If the assumption is made that, on average, people live a half year on the year of their death, the complete life expectancy at age $x$ would be $e\_x\; +\; 1/2$, which is denoted by e̊_x, and is the intuitive definition of life expectancy.

By definition, life expectancy is an arithmetic mean. It can also be calculated by integrating the survival curve from 0 to positive infinity (or equivalently to the maximum lifespan, sometimes called 'omega'). For an extinct or completed cohort (all people born in the year 1850, for example), it can of course simply be calculated by averaging the ages at death. For cohorts with some survivors, it is estimated by using mortality experience in recent years. The estimates are called period cohort life expectancies.

The starting point for calculating life expectancy is the age-specific death rates of the population members. If a large amount of data is available, a statistical population can be created that allow the age-specific death rates to be simply taken as the mortality rates actually experienced at each age (the number of deaths divided by the number of years "exposed to risk" in each data cell). However, it is customary to apply smoothing to remove (as much as possible) the random statistical fluctuations from one year of age to the next. In the past, a very simple model used for this purpose was the Gompertz function, but more sophisticated methods are now used.{{cite journal|vauthors=Anderson RN|title=A method for constructing complete annual U.S. life tables|journal=Vital and Health Statistics. Series 2, Data Evaluation and Methods Research|issue=129|pages=1–28|date=2000|pmid=11824050|url=https://www.cdc.gov/nchs/data/series/sr_02/sr02_129.pdf}} The most common modern methods include:

• fitting a mathematical formula (such as the Gompertz function, or an extension of it) to the data.
• looking at an established mortality table derived from a larger population and making a simple adjustment to it (such as multiplying by a constant factor) to fit the data. (In cases of relatively small amounts of data.)
• looking at the mortality rates actually experienced at each age and applying a piecewise model (such as by cubic splines) to fit the data. (In cases of relatively large amounts of data.)

File:BahnhofsuhrZuerich RZ.jpg reduces life expectancy by 20 minutes.{{Cite news |author1=Sarah Jackson |author2=Martin Jarvis |author3=Robert West |title=The price of a cigarette: 20 minutes of life? |url=https://onlinelibrary.wiley.com/doi/10.1111/add.16757 |work=Addiction |date=29 December 2024 |access-date=22 January 2025}}{{Cite news |author=Ian Sample |title=Single cigarette takes 20 minutes off life expectancy, study finds |url=https://www.theguardian.com/society/2024/dec/30/single-cigarette-takes-20-minutes-off-life-expectancy-study |work=The Guardian |date=30 December 2024 |access-date=22 January 2025}}]]

The age-specific death rates are calculated separately for separate groups of data that are believed to have different mortality rates (such as males and females, or smokers and non-smokers) and are then used to calculate a life table from which one can calculate the probability of surviving to each age. While the data required are easily identified in the case of humans, the computation of life expectancy of industrial products and wild animals involves more indirect techniques. The life expectancy and demography of wild animals are often estimated by capturing, marking, and recapturing them.{{cite book|vauthors=Young LJ, Young JH|author-link1=Linda J. Young|date=1998|title=Statistical ecology: a population perspective.|location=Boston|publisher=Kluwer Academic Publishers|page=310|isbn=978-0-412-04711-4}} The life of a product, more often termed shelf life, is also computed using similar methods. In the case of long-lived components, such as those used in critical applications (e.g. aircraft), methods like accelerated aging are used to model the life expectancy of a component.

The life expectancy statistic is usually based on past mortality experience and assumes that the same age-specific mortality rates will continue. Thus, such life expectancy figures need to be adjusted for temporal trends before calculating how long a currently living individual of a particular age is expected to live. Period life expectancy remains a commonly used statistic to summarize the current health status of a population. However, for some purposes, such as pensions calculations, it is usual to adjust the life table used by assuming that age-specific death rates will continue to decrease over the years, as they have usually done in the past. That is often done by simply extrapolating past trends, but some models exist to account for the evolution of mortality, like the Lee–Carter model.{{cite journal|vauthors=Lee RD, Carter LR|title=Modeling and forecasting US mortality.|journal=Journal of the American Statistical Association|date=September 1992|volume=87|issue=419|pages=659–671|doi=10.1080/01621459.1992.10475265}}

As discussed above, on an individual basis, some factors correlate with longer life. Factors that are associated with variations in life expectancy include family history, marital status, economic status, physique, exercise, diet, drug use (including smoking and alcohol consumption), disposition, education, environment, sleep, climate, and health care.

To assess the quality of these additional years of life, 'healthy life expectancy' has been calculated for the last 30 years. Since 2001, the World Health Organization has published statistics called Healthy life expectancy (HALE), defined as the average number of years that a person can expect to live in "full health" excluding the years lived in less than full health due to disease and/or injury.{{cite web|url=https://www.who.int/data/gho/indicator-metadata-registry/imr-details/healthy-life-expectancy-(hale)-at-60-(years)|title=Healthy life expectancy (HALE) at 60 (years)|publisher=World Health Organization}}{{cite web|url=https://www.who.int/healthinfo/statistics/indhale/en/|archive-url=https://web.archive.org/web/20120704092005/http://www.who.int/healthinfo/statistics/indhale/en/|url-status=dead|archive-date=4 July 2012|title=Health Status Statistics: Mortality|publisher=World Health Organization}} Since 2004, Eurostat publishes annual statistics called Healthy Life Years (HLY) based on reported activity limitations. The United States uses similar indicators in the framework of the national health promotion and disease prevention plan "Healthy People 2010". More and more countries are using health expectancy indicators to monitor the health of their population.

File:HALE vs GDP.png

The long-standing quest for longer life led in the 2010s to a more promising focus on increasing HALE, also known as a person's "healthspan". Besides the benefits of keeping people healthier longer, a goal is to reduce health-care expenses on the many diseases associated with cellular senescence. Approaches being explored include fasting, exercise, and senolytic drugs.{{cite magazine|url=https://www.newscientist.com/article/mg24232270-100-anti-ageing-drugs-are-coming-that-could-keep-you-healthier-for-longer/|vauthors=Lawton G|title=Anti-ageing drugs are coming that could keep you healthier for longer|date=2019-04-24|website=New Scientist|access-date=2019-05-02}}

Forecasting life expectancy and mortality form an important subdivision of demography. Future trends in life expectancy have huge implications for old-age support programs (like U.S. Social Security and pension) since the cash flow in these systems depends on the number of recipients who are still living (along with the rate of return on the investments or the tax rate in pay-as-you-go systems). With longer life expectancies, the systems see increased cash outflow; if the systems underestimate increases in life-expectancies, they will be unprepared for the large payments that will occur, as humans live longer and longer.

Life expectancy forecasting is usually based on one of two different approaches:

1. Forecasting the life expectancy directly, generally using ARIMA or other time-series extrapolation procedures. This has the advantage of simplicity, but it cannot account for changes in mortality at specific ages, and the forecast number cannot be used to derive other life table results. Analyses and forecasts using this approach can be done with any common statistical/mathematical software package, like EViews, R, SAS, Stata, Matlab, or SPSS.
2. Forecasting age-specific death rates and computing the life expectancy from the results with life table methods. This is usually more complex than simply forecasting life expectancy because the analyst must deal with correlated age-specific mortality rates, but it seems to be more robust than simple one-dimensional time series approaches. It also yields a set of age-specific rates that may be used to derive other measures, such as survival curves or life expectancies at different ages. The most important approach in this group is the Lee-Carter model,{{cite web|url=http://www.soa.org/library/journals/north-american-actuarial-journal/2000/january/naaj0001_5.pdf|title=The Lee-Carter Method for Forecasting Mortality, with Various Extensions and Applications – SOA|publisher=SOA|access-date=9 April 2018|archive-date=7 March 2019|archive-url=https://web.archive.org/web/20190307054148/https://www.soa.org/library/journals/north-american-actuarial-journal/2000/january/naaj0001_5.pdf|url-status=dead}} which uses the singular value decomposition on a set of transformed age-specific mortality rates to reduce their dimensionality to a single time series, forecasts that time series, and then recovers a full set of age-specific mortality rates from that forecasted value. The software includes Professor Rob J. Hyndman's [https://web.archive.org/web/20100822170736/http://robjhyndman.com/software/demography/ R package called 'demography'] and [http://lcfit.demog.berkeley.edu/ UC Berkeley's LCFIT system].

Life expectancy is one of the factors in measuring the Human Development Index (HDI) of each nation along with adult literacy, education, and standard of living.{{cite web|url=http://hdrstats.undp.org/indicators/6.html|title=International Human Development Indicators—UNDP|publisher=Hdrstats.undp.org|access-date=4 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20090420030845/http://hdrstats.undp.org/indicators/6.html|archive-date=20 April 2009}}

Life expectancy is used in describing the physical quality of life of an area. It is also used for an individual when the value of a life settlement is determined a life insurance policy is sold for a cash asset.{{Clarify|reason=Hard to understand due to sentence structure and wording.|date=November 2022}}

Disparities in life expectancy are often cited as demonstrating the need for better medical care or increased social support. A strongly associated indirect measure is income inequality. For the top 21 industrialized countries, if each person is counted equally, life expectancy is lower in more unequal countries (r = −0.907).{{cite journal|vauthors=De Vogli R, Mistry R, Gnesotto R, Cornia GA|title=Has the relation between income inequality and life expectancy disappeared? Evidence from Italy and top industrialised countries|journal=Journal of Epidemiology and Community Health|volume=59|issue=2|pages=158–162|date=February 2005|pmid=15650149|pmc=1733006|doi=10.1136/jech.2004.020651|doi-access=free}} There is a similar relationship among states in the U.S. (r = −0.620).{{cite journal|vauthors=Kaplan GA, Pamuk ER, Lynch JW, Cohen RD, Balfour JL|title=Inequality in income and mortality in the United States: analysis of mortality and potential pathways|journal=The BMJ|volume=312|issue=7037|pages=999–1003|date=April 1996|pmid=8616393|pmc=2350835|doi=10.1136/bmj.312.7037.999|doi-access=free}}

File:20200101 Remaining life expectancy - US.svg planning.{{cite web|date=2020|title=Actuarial Life Table|url=https://www.ssa.gov/oact/STATS/table4c6.html|url-status=live|archive-url=https://web.archive.org/web/20230708231105/https://www.ssa.gov/oact/STATS/table4c6.html|archive-date=8 July 2023|publisher=U.S. Social Security Administration Office of Chief Actuary}}]]

Life expectancy may be confused with the average age an adult could expect to live, creating the misunderstanding that an adult's lifespan would be unlikely to exceed their life expectancy at birth. This is not the case, as life expectancy is an average of the lifespans of all individuals, including those who die before adulthood. One may compare the life expectancy of the period after childhood to estimate also the life expectancy of an adult.

As a measure of the years of life remaining, life expectancy decreases with age after initially rising in early childhood, but the average age to which a person is likely to live increases as they survive to successive higher ages.{{cite web|url=http://www.infoplease.com/ipa/A0005140.html|title=Life Expectancy by Age, 1850–2011|website=InfoPlease}} In the table above, the estimated modern hunter-gatherer average expectation of life at birth of 33 years (often considered an upper-bound for Paleolithic populations) equates to a life expectancy at 15 of 39 years, so that those surviving to age 15 will on average die at 54.

In England in the 13th–19th centuries with life expectancy at birth rising from perhaps 25 years to over 40, expectation of life at age 30 has been estimated at 20–30 years,{{cite web|vauthors=Khan-ad-Din FM, Caidan Pentathlon M|title=Old Age, Height and Nutrition: Common Misconceptions About Medieval England|url=http://sirguillaume.com/wp-content/uploads/2012/01/Old_Age-Height-Nutrition.pdf|access-date=28 January 2021|archive-date=7 February 2021|archive-url=https://web.archive.org/web/20210207054819/http://sirguillaume.com/wp-content/uploads/2012/01/Old_Age-Height-Nutrition.pdf|url-status=dead}} giving an average age at death of about 50–60 for those (a minority at the start of the period but two-thirds at its end) surviving beyond their twenties.

File:20200101 Life expectancy increases with age already achieved - chart.svg

The table above gives the life expectancy at birth among 13th-century English nobles as 30–33, but having surviving to the age of 21, a male member of the English aristocracy could expect to live:

• 1200–1300: to age 64
• 1300–1400: to age 45 (because of the bubonic plague)
• 1400–1500: to age 69
• 1500–1550: to age 71

A further concept is that of modal age at death, the single age when deaths among a population are more numerous than at any other age. In all pre-modern societies the most common age at death is the first year of life: it is only as infant mortality falls below around 33–34 per thousand (roughly a tenth of estimated ancient and medieval levels) that deaths in a later year of life (usually around age 80) become more numerous. While the most common age of death in adulthood among modern hunter-gatherers (often taken as a guide to the likely most favourable Paleolithic demographic experience) is estimated to average 72 years,{{citation|vauthors=Gurven M, Kaplan H|title=Longevity Among Hunter- Gatherers: A Cross-Cultural Examination|journal=Population and Development Review|volume=33|issue=2|pages=321–365|year=2007|doi=10.1111/j.1728-4457.2007.00171.x}} the number dying at that age is dwarfed by those (over a fifth of all infants) dying in the first year of life, and only around a quarter usually survive to the higher age.

Maximum life span is an individual-specific concept, and therefore is an upper bound rather than an average.{{citation|url=https://books.google.com/books?id=oIJ5TKh7mPgC&q=%22this+is+one+of+the+biggest+misconceptions+about+old+age%22&pg=PA70|author-link=Christopher Wanjek|vauthors=Wanjek C|title=Bad Medicine: Misconceptions and Misuses Revealed, from Distance Healing to Vitamin O|publisher=Wiley|year=2002|pages=70–71|isbn=978-0-471-43499-3|postscript=.}} Science author Christopher Wanjek writes, "[H]as the human race increased its life span? Not at all. This is one of the biggest misconceptions about old age: we are not living any longer." The maximum life span, or oldest age a human can live, may be constant. Further, there are many examples of people living significantly longer than the average life expectancy of their time period, such as Socrates (71), Saint Anthony the Great (105), Michelangelo (88), and John Adams (90).

However, anthropologist John D. Hawks criticizes the popular conflation of life span (life expectancy) and maximum life span when popular science writers falsely imply that the average adult human does not live longer than their ancestors. He writes, "[a]ge-specific mortality rates have declined across the adult lifespan. A smaller fraction of adults die at 20, at 30, at 40, at 50, and so on across the lifespan. As a result, we live longer on average... In every way we can measure, human lifespans are longer today than in the immediate past, and longer today than they were 2000 years ago... age-specific mortality rates in adults really have reduced substantially."{{citation|url=http://johnhawks.net/weblog/reviews/life_history/age-specific-mortality-lifespan-bad-science-2009.html|author-link=John D. Hawks|vauthors=Hawks J|title=Human lifespans have not been constant for the last 2000 years|year=2009|postscript=.}}

{{Columns-list|colwidth=30em|

• Biodemography
• Calorie restriction
• Demography
• Depreciation
• DNA damage theory of aging
• Glasgow effect
• Health equity
• Life extension
• Life table
• Lindy effect
• List of countries by life expectancy
• List of countries by past life expectancy
• List of longest-living organisms
• LGBT life expectancy
• Maximum life span
• Medieval demography
• Mitohormesis
• Mortality rate
• Population pyramid
• Senescence

}}

{{Columns-list|colwidth=30em|

• Strategies for engineered negligible senescence (SENS)
• John Sperling
• Life extension
• Longevity
• Rejuvenation
• Public health
• Infant mortality

}}

{{notelist|refs=

{{efn |name=exsymbol |In standard actuarial notation, e{{sub|x}} refers to the expected future lifetime of (x) in whole years, while eͦ{{sub|x}} (with a ring above the e) denotes the complete expected future lifetime of (x), including the fraction.}}

}}

{{Reflist}}

{{refbegin}}

• Riley, James C. Rising Life Expectancy (Cambridge UP, 2001).
• {{cite book|vauthors=Gavrilov LA, Gavrilova NS|author-link1=Leonid A. Gavrilov|date=1991|title=The Biology of Life Span: A Quantitative Approach|location=New York|publisher=Harwood Academic Publisher|isbn=978-3-7186-4983-9}}
• {{cite book|vauthors=Kochanek KD, Arias E, Anderson RN|date=2013|url=https://purl.fdlp.gov/GPO/gpo41789|title=How Did Cause of Death Contribute to Racial Differences in Life Expectancy in the United States in 2010?|location=Hyattsville, Md.|publisher=U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics}}

{{refend}}

{{Commons category|Life expectancy}}

• [http://www.google.com/publicdata/explore?ds=wb-wdi&met=sp_dyn_le00_in&idim=country:CAN&dl=en&q=average+life+expectancy+canada#met=sp_dyn_le00_in&idim=country:USA:CHN Charts for all countries]
• [https://web.archive.org/web/20160331014445/http://ourworldindata.org/data/population-growth-vital-statistics/life-expectancy/ Our World In Data – Life Expectancy]—Visualizations of how life expectancy around the world has changed historically (by Max Roser). Includes life expectancy for different age groups. Charts for all countries, world maps, and links to more data sources.
• [http://www.helpage.org/global-agewatch/population-ageing-data/ Global Agewatch has the latest internationally comparable statistics on life expectancy from 195 countries.] {{Webarchive|url=https://web.archive.org/web/20141003130501/http://www.helpage.org/global-agewatch/population-ageing-data/ |date=3 October 2014 }}
• [https://www.cia.gov/library/publications/the-world-factbook/rankorder/2102rank.html Rank Order—Life expectancy at birth] {{Webarchive|url=https://web.archive.org/web/20181229134543/https://www.cia.gov/library/publications/the-world-factbook/rankorder/2102rank.html |date=29 December 2018 }} from the CIA's World Factbook.
• [https://www.cdc.gov/nchs/nvss/life-expectancy.htm Annual Life Tables since 1966; Decennial Life Tables since 1890] from the US Centers for Disease Controls and Prevention, National Center for Health Statistics.
• [https://web.archive.org/web/20120427061404/http://www.utexas.edu/depts/classics/documents/Life.html Life expectancy in Roman times] from the University of Texas.
• Animal lifespans: [https://web.archive.org/web/20060427184844/http://www.tesarta.com/www/resources/library/lifespans.html Animal Lifespans] from Tesarta Online (Internet Archive); [http://www.sonic.net/~petdoc/lifespan.htm The Life Span of Animals] from Dr. Bob's All Creatures Site.

{{Longevity}}

{{Authority control}}

{{DEFAULTSORT:Life Expectancy}}

Category:Actuarial science

Category:Demographic economics

Category:Senescence

Category:Demography

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