health effects of tea

{{further|Aluminium#Toxicity}}

Tea drinking accounts for a high proportion of aluminum in the human diet.{{cite journal |doi=10.1016/j.foodchem.2007.03.019 |journal=Food Chemistry |volume=104 |issue=4 |year=2007 |pages=1662–1669 |vauthors=Streeta R, Drábeka O, Szákováb J, Mládkováa L |title=Total content and speciation of aluminium in tea leaves and tea infusions}} The levels are safe, but there has been some concern that aluminum traces may be associated with Alzheimer's disease. A 2013 study additionally indicated that some teas contained lead (mostly Chinese) and aluminum (Indian/Sri Lanka blends, China).{{cite journal | title=The Benefits and Risks of Consuming Brewed Tea: Beware of Toxic Element Contamination | doi=10.1155/2013/370460 | pmid=24260033 | pmc=3821942 | journal=Journal of Toxicology | pages=1–8| year=2013 | last1=Schwalfenberg | first1=Gerry | last2=Genuis | first2=Stephen J. | last3=Rodushkin | first3=Ilia | doi-access=free }} There is still insufficient evidence to draw firm conclusions on this subject.{{cite journal |journal=Food Research International |volume=43 |issue=9 |year=2010 |pages=2234–2252 |title=Trace elements in tea leaves, made tea and tea infusion: A review |type=Review |vauthors=Karak T, Bhagat RM |doi=10.1016/j.foodres.2010.08.010}}

Most studies have found no association between tea intake and iron absorption.{{cite journal|journal=Nutrients|year=2014|volume=6|issue=9|pages=3747–76|doi=10.3390/nu6093747|title=Dietary determinants of and possible solutions to iron deficiency for young women living in industrialized countries: a review|vauthors=Beck KL, Conlon CA, Kruger R, Coad J |pmid=25244367|pmc=4179187|doi-access=free}} However, drinking excessive amounts of black tea may inhibit the absorption of iron, and may harm people with anaemia.{{cite journal |vauthors=Wierzejska R |title=Tea and health—a review of the current state of knowledge |journal=Przegl Epidemiol |volume=68 |issue=3 |pages=501–6, 595–9 |year=2014 |pmid=25391016 |type=Review}}

Concerns have been raised about the traditional method of over-boiling tea to produce a decoction, which may increase the amount of environmental contaminants released and consumed.{{cite journal|journal=Food Addit Contam Part a Chem Anal Control Expo Risk Assess|year=2014|volume=31|issue=11|pages=1794–804|title=Residues and contaminants in tea and tea infusions: a review|vauthors=Abd El-Aty AM, Choi JH, Rahman MM, Kim SW, Tosun A, Shim JH |pmid=25164107|doi=10.1080/19440049.2014.958575|s2cid=21497059}}

{{See also|Fluoride toxicity}}

All tea leaves contain fluoride; however, mature leaves contain as much as 10 to 20 times the fluoride levels of young leaves from the same plant.{{cite journal |vauthors=Lung SC, Cheng HW, Fu CB |title=Potential exposure and risk of fluoride intakes from tea drinks produced in Taiwan |journal=J Expo Sci Environ Epidemiol |volume=18 |issue=2 |pages=158–66 |year=2008 |pmid=17410113 |doi=10.1038/sj.jes.7500574|doi-access=free |bibcode=2008JESEE..18..158L }}{{cite journal |vauthors=Malinowska E, Inkielewicz I, Czarnowski W, Szefer P |title=Assessment of fluoride concentration and daily intake by human from tea and herbal infusions |journal=Food Chem. Toxicol. |volume=46 |issue=3 |pages=1055–61 |year=2008 |pmid=18078704 |doi=10.1016/j.fct.2007.10.039}}

The fluoride content of a tea leaf depends on the leaf picking method used and the fluoride content of the soil from which it has been grown; tea plants absorb this element at a greater rate than other plants. Care in the choice of the location where the plant is grown may reduce the risk.{{cite journal | title = Accumulation of Fluoride and Aluminium Related to Different Varieties of Tea Plant |author1=Jianyun Ruan |author2=Ming H. Wong | journal = Environmental Geochemistry and Health | volume = 23 | issue = 1 | pages = 53–63 | year = 2001 | doi = 10.1023/A:1011082608631|bibcode=2001EnvGH..23...53R |s2cid=127931635 }} It is speculated that hand-picked tea would contain less fluoride than machine-harvested tea, because there is a much lower chance of harvesting older leaves during the harvest process. A 2013 British study of 38 teas found that cheaper UK supermarket tea blends had the highest levels of fluoride with about 580 mg per kilogram, green teas averaged about 397 mg per kg and pure blends about 132 mg per kg. The researchers suggested that economy teas may use older leaves which contain more fluoride. They calculated a person drinking a litre of economy tea per day would consume about 6 mg of fluoride, above the recommended average dietary intake level of 3–4 mg of fluoride per day, but below the maximum tolerable amount of 10 mg of fluoride per day.(25 July 2013) [http://www.nhs.uk/news/2013/07July/Pages/do-fluoride-levels-in-cheap-tea-pose-a-health-risk.aspx Do fluoride levels in cheap tea pose a health risk?] British National Health Service "Choices, Retrieved 26 July 2013 Brick tea, made from fallen leaves, old leaves and stems has the highest levels.{{Cite journal |vauthors=Fung KF, Zhang ZQ, Wong JW, Wong MH | title = Fluoride contents in tea and soil from tea plantations and the release of fluoride into tea liquor during infusion | doi = 10.1016/S0269-7491(98)00187-0 |journal = Environmental Pollution |volume = 104 |issue = 2 |pages = 197–205 |year=1999 }}

One study indicated that green tea leaves have an average fluoride concentration of 52 mg/kg, and approximately 89% of the fluoride was released from the leaves into tea after brewing.{{cite journal |last1=Maleki |first1=Afshin |last2=Daraei |first2=Hiua |last3=Mohammadi |first3=Elham |last4=Zandi |first4=Shiva |last5=Teymouri |first5=Pari |last6=Mahvi |first6=Amir Hossien |last7=Gharibi |first7=Fardin |title=Daily Fluoride Intake from Iranian Green Tea: Evaluation of Various Flavorings on Fluoride Release |pmc=4811265|pmid=27042093|journal=Environmental Health Insights |pages=59–63 |doi=10.4137/EHI.S38511 |date=28 March 2016|volume=10 |bibcode=2016EnvHI..10S8511M }}

Tea contains oxalate, overconsumption of which can cause kidney stones, as well as binding with free calcium in the body. The bioavailability of oxalate from tea is low, thus a possible negative effect requires a large intake of tea.{{cite journal

| title = Low oxalate bioavailability from black tea

|author1=Michael Liebman |author2=Shawnna Murphy | journal = Nutrition Research

| volume = 27

| issue = 5

| pages = 273–278h

| year = 2007

| doi = 10.1016/j.nutres.2007.04.004 }} Massive black tea consumption has been linked to kidney failure due to its high oxalate content (acute oxalate nephropathy).{{Cite web|last=Emery|first=Gene|date=1 April 2015|title=Massive tea consumption linked to kidney failure|url=https://www.reuters.com/article/us-tea-overdose-kidney-damage/massive-tea-consumption-linked-to-kidney-failure-idUSKBN0MS5FT20150401|url-status=dead|archive-url=https://web.archive.org/web/20180307124731/https://www.reuters.com/article/us-tea-overdose-kidney-damage/massive-tea-consumption-linked-to-kidney-failure-idUSKBN0MS5FT20150401|archive-date=7 March 2018|access-date=13 December 2020|work=Reuters}}Elahe Izadi washingtonpost.com [https://www.washingtonpost.com/news/to-your-health/wp/2015/04/03/this-mans-kidneys-failed-after-he-drank-too-much-iced-tea/ Why drinking too much iced tea caused this man’s kidneys to fail] 3 April 2015

{{see also|Health effects of caffeine}}

Tea also contains theanine and the stimulant caffeine at about 3% of its dry weight, translating to between 30 mg and 90 mg per {{convert|8|usoz|mL}} depending on type, brand{{cite book |author1=Bennett Alan Weinberg |author2=Bonnie K. Bealer |title=The World of Caffeine: The Science and Culture of the World's Most Popular Drug |url=https://archive.org/details/worldofcaffeines00benn |url-access=registration |publisher=Routledge |year=2001 |isbn=978-0-415-92722-2 |access-date=2008-09-20 |page=[https://archive.org/details/worldofcaffeines00benn/page/228 228]}} and brewing method.M. B. Hicks, Y-H. P. Hsieh, L. N. Bell, Tea preparation and its influence on methylxanthine concentration, Food Research International 29(3–4) 325–330 (1996) Tea also contains small amounts of theobromine and theophylline.Graham H. N.; Green tea composition, consumption, and polyphenol chemistry; Preventive Medicine 21(3):334-50 (1992) Dry tea has more caffeine by weight than dry coffee; nevertheless, more dry coffee than dry tea is used in typical drink preparations,{{cite web |url=http://www.stashtea.com/caffeine+and+tea+information.aspx |title=Caffeine and Tea Information |publisher=Stash Tea |access-date=2009-07-15 |archive-url=https://web.archive.org/web/20110513060419/http://www.stashtea.com/caffeine+and+tea+information.aspx |archive-date=13 May 2011 |url-status=dead }} which results in a cup of brewed tea containing significantly less caffeine than a cup of coffee of the same size.

The caffeine in tea is a mild diuretic. However, the British Dietetic Association has suggested that tea can be used to supplement normal water consumption, and that "the style of tea and coffee and the amounts we drink in the UK are unlikely to have a negative effect [on hydration]".[http://www.bda.uk.com/news/110610DehydrationWeek.pdf BDA Supports Dehydration Awareness Week with some Handy Tips (PDF)]. British Dietetic Association, June 2011.

Drinking caffeinated tea may improve mental alertness due to the effects of caffeine.

In 2011, the US Food and Drug Administration reported that there was little evidence to support the claim that green tea consumption may reduce the risk of breast and prostate cancer.{{cite web|title=Summary of Qualified Health Claims Subject to Enforcement Discretion|url=https://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm073992.htm#gtea|author=Food and Drug Administration|website=Food and Drug Administration |date=24 February 2011|access-date= 9 October 2014|author-link=Food and Drug Administration}}

A 2010 report by the US National Cancer Institute stated that epidemiological studies and the few clinical trials of tea for the prevention of cancer were inconclusive. The institute "does not recommend for or against the use of tea to reduce the risk of any type of cancer." ... "Inconsistencies in study findings regarding tea and cancer risk may be due to variability in tea preparation, tea consumption, the bioavailability of tea compounds (the amounts that can be absorbed by the body), lifestyle differences, and individual genetic differences."{{cite web|title=Tea and Cancer Prevention: Strengths and Limits of the Evidence|author=National Cancer Institute|url= http://www.cancer.gov/cancertopics/factsheet/prevention/tea|access-date=7 December 2022|date=17 November 2010}} Though there is some positive evidence for risk reduction of breast, prostate, ovarian, and endometrial cancers with green tea, it is weak and inconclusive.{{cite journal |vauthors=Johnson R, Bryant S, Huntley AL |title=Green tea and green tea catechin extracts: an overview of the clinical evidence |journal=Maturitas |volume=73 |issue=4 |pages=280–7 | date=December 2012 |pmid=22986087 |doi=10.1016/j.maturitas.2012.08.008 |type=Review |quote=Green tea consumption does help reduce body weight and aid weight management as shown in short term RCTs (12 weeks) but not to a clinically relevant level.|doi-access=free }}

Meta-analyses of observational studies have concluded that black tea consumption does not appear to protect against the development of oral cancers in Asian or Caucasian populations, the development of esophageal cancer or prostate cancer in Asian populations, or the development of lung cancer.{{cite journal|vauthors=Wang W, Yang Y, Zhang W, Wu W |title=Association of tea consumption and the risk of oral cancer: a meta-analysis|journal=Oral Oncol|volume=50|issue=4|pages=276–81|date=April 2014|pmid=24389399|doi=10.1016/j.oraloncology.2013.12.014|type=Meta-Analysis}}{{cite journal|vauthors=Wang Y, Yu X, Wu Y, Zhang D |title=Coffee and tea consumption and risk of lung cancer: a dose-response analysis of observational studies|journal=Lung Cancer|volume=78|issue=2|pages=169–70|date=November 2012|pmid=22964413|doi=10.1016/j.lungcan.2012.08.009|type=Meta-Analysis}}{{cite journal|vauthors=Zheng J, Yang B, Huang T, Yu Y, Yang J, Li D |title=Green tea and black tea consumption and prostate cancer risk: an exploratory meta-analysis of observational studies|journal=Nutr Cancer|volume=63|issue=5|pages=663–72|date=June 2011|pmid=21667398|doi=10.1080/01635581.2011.570895|s2cid=21567675|type=Meta-Analysis}}{{cite journal|vauthors=Lin YW, Hu ZH, Wang X, Mao QQ, Qin J, Zheng XY, Xie LP |title=Tea consumption and prostate cancer: an updated meta-analysis|journal=World J Surg Oncol|volume=12|pages=38|date=February 2014|pmid=24528523|pmc=3925323|doi=10.1186/1477-7819-12-38|type=Meta-Analysis |doi-access=free }}{{cite journal|vauthors=Zheng JS, Yang J, Fu YQ, Huang T, Huang YJ, Li D |title=Effects of green tea, black tea, and coffee consumption on the risk of esophageal cancer: a systematic review and meta-analysis of observational studies|journal=Nutr Cancer|volume=65|issue=1|pages=1–16|date=January 2013|pmid=23368908|doi=10.1080/01635581.2013.741762|s2cid=8612872|type=Systematic Review and Meta-Analysis}} In 2018, a meta-analysis based on 14 case-control studies found that tea consumption appears protective of oral cancer with a greater decrease in risk occurring with a larger intake (except for black tea and American people).{{cite journal |last1=Zhou |first1=Hao |last2=Wu |first2=Weiwei |last3=Wang |first3=Fengqin |last4=Qi |first4=Huizhong |last5=Cheng |first5=Zhigang |title=Tea consumption is associated with decreased risk of oral cancer |journal=Medicine |date=21 December 2018 |volume=97 |issue=51 |pages=e13611 |doi=10.1097/MD.0000000000013611 |pmc=6320052|pmid=30572470|issn=0025-7974}}

The consumption of very hot tea could increase the risk of esophageal cancer.{{cite journal |last1=Zhong |first1=Y |last2=Yang |first2=C |last3=Wang |first3=N |last4=Pan |first4=D |last5=Wang |first5=S |last6=Sun |first6=G |title=Hot Tea Drinking and the Risk of Esophageal Cancer: A Systematic Review and Meta-Analysis. |journal=Nutrition and Cancer |date=2022 |volume=74 |issue=7 |pages=2384–2391 |doi=10.1080/01635581.2021.2007963 |pmid=34818954|s2cid=244682963 }}

In preliminary long-term clinical studies, black tea consumption showed evidence for providing a small reduction in the risk of stroke,{{cite journal|vauthors=Shen L, Song LG, Ma H, Jin CN, Wang JA, Xiang MX |title=Tea consumption and risk of stroke: a dose-response meta-analysis of prospective studies|journal=J Zhejiang Univ Sci B|volume=13|issue=8|pages=652–62|date=August 2012|pmid=22843186|pmc=3411099|doi=10.1631/jzus.B1201001|type=Review}}{{cite journal|author=Larsson SC|title=Coffee, tea, and cocoa and risk of stroke|journal=Stroke|volume=45|issue=1|pages=309–14|date=January 2014|pmid=24326448|doi=10.1161/STROKEAHA.113.003131|type=Review|doi-access=free}} whereas, in another review, green tea and black tea did not have significant effects on the risk of coronary heart disease.{{Cite journal|last1=Wang|first1=Ze-Mu|last2=Zhou|first2=Bo|last3=Wang|first3=Yong-Sheng|last4=Gong|first4=Qing-Yue|last5=Wang|first5=Qi-Ming|last6=Yan|first6=Jian-Jun|last7=Gao|first7=Wei|last8=Wang|first8=Lian-Sheng|date=2011-03-01|title=Black and green tea consumption and the risk of coronary artery disease: a meta-analysis|journal=The American Journal of Clinical Nutrition|volume=93|issue=3|pages=506–515|doi=10.3945/ajcn.110.005363|issn=1938-3207|pmid=21248184|doi-access=free}} Two reviews of randomized controlled trials concluded that long-term consumption of black tea slightly lowers systolic and diastolic blood pressures (about 1–2 mmHg), a finding based on limited evidence.{{cite journal|vauthors=Hartley L, Flowers N, Holmes J, Clarke A, Stranges S, Hooper L, Rees K |title=Green and black tea for the primary prevention of cardiovascular disease|journal=Cochrane Database Syst Rev|volume=2013|issue=6|pages=CD009934|date=June 2013|pmid=23780706|doi=10.1002/14651858.CD009934.pub2|pmc=7433290|type=Systematic Review and Meta-Analysis|url=http://wrap.warwick.ac.uk/60046/1/WRAP_Clarke_CD009934%20%281%29.pdf}}{{cite journal|vauthors=Liu G, Mi XN, Zheng XX, Xu YL, Lu J, Huang XH |title=Effects of tea intake on blood pressure: a meta-analysis of randomised controlled trials|journal=Br J Nutr|volume=112|issue=7|pages=1043–54|date=October 2014|pmid=25137341|doi=10.1017/S0007114514001731|type=Meta-Analysis|doi-access=free}} A 2013 Cochrane review found some evidence of benefit from tea consumption on cardiovascular markers (total and LDL cholesterol), though more research is needed.

Tea consumption does not appear to affect the risk of bone fracture including hip fractures or fractures of the humerus in men or women.{{cite journal|vauthors=Chen B, Shi HF, Wu SC |title=Tea consumption didn't modify the risk of fracture: a dose-response meta-analysis of observational studies|journal=Diagn Pathol|volume=9|pages=44|date=March 2014|pmid=24588938|pmc=4017777|doi=10.1186/1746-1596-9-44 |doi-access=free }}

Although green tea is commonly believed to be a weight loss aid, there is no good evidence that its long-term consumption has any meaningful benefit in helping overweight or obese people to lose weight, or that it helps to maintain a healthy body weight.{{cite journal |vauthors=Jurgens TM, Whelan AM, Killian L, Doucette S, Kirk S, Foy E |title=Green tea for weight loss and weight maintenance in overweight or obese adults |journal=Cochrane Database Syst Rev |volume=2012 |pages=CD008650 |year=2012 |issue=12 |pmid=23235664 |doi=10.1002/14651858.CD008650.pub2 |type=Systematic review|pmc=8406948 }}{{cite journal | vauthors = Kovacs EM | title = Effects of green tea on weight maintenance after body-weight loss | journal = British Journal of Nutrition | date=March 2004 | volume = 91 | issue = 3 | pages = 431–437 | doi=10.1079/BJN20041061 | pmid = 15005829 | doi-access = free }} Use of green tea for attempted weight loss carries a small risk of adverse effects, such as nausea, constipation, and stomach discomfort.

• Coffee
• Decaffeination
• Detox tea
• gamma-Glutamylmethylamide
• Health effects of coffee
• Phenolic content in tea
• Release of microplastics by tea bags
• Traditional medicine

{{reflist}}

• [http://www.cancer.gov/newscenter/pressreleases/tea Tea and Cancer Prevention] – National Cancer Institute press release
• [https://www.drugs.com/npp/green-tea.html Green Tea (an overview from Drugs.com)]

{{Teas}}

{{Health effects of}}

{{DEFAULTSORT:Health Effects of Tea}}

Category:Tea

Tea