Potential effects of tea on health

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Bai Hao Yin Zhen white tea
Bai Hao Yin Zhen white tea
Note: this page only deals with the effects of tea which is made from the plant Camellia sinensis (i.e. black tea, oolong tea, green tea and white tea). This page does not deal with the effects of other teas.

The health benefits of tea have been touted for infusions made from the plant Camellia sinensis for over 4700 years; ever since its discovery was attributed to the legendary emperor, Shennong. The Shen Nong Ben Cao Jing claimed its taste and stimulative properties were useful for treating tumors, abscesses, bladder ailments, lethargy, among other conditions.[1] The possible beneficial health effects of tea consumption have been suggested and supported by some studies, but others have found no beneficial effects. The studies contrast other claims, including antinutritional effects such as preventing absorption of iron and protein, usually attributed to tannin. The vast majority of studies have been of Green tea, however some studies have been made of the other types of tea derived from Camellia sinensis such as White tea, Oolong tea, and Black tea. Green tea has been claimed[2] to be helpful for atherosclerosis, bad cholesterol, cancer, inflammatory bowel disease, diabetes, liver disease, weight loss, cognitive impairment, and even halitosis.

Contents

[edit] Potential benefits

[edit] Anti-cancer properties

An article in New Scientist magazine[3] mentions that numerous studies suggest that green tea protects against a range of cancers, including lung, prostate and breast cancer. The reason cited is the antioxidant epigallocatechin gallate (EGCG), according to Hirofumi Tachibana's team at Kyushu University in Japan. Their research showed that growth of human lung cancer cells that have a cell receptor called 67 LR is slowed significantly after drinking just two or three cups of green tea, which contains EGCG. The research also showed that 67 LR is involved in the propagation of prion diseases such as mad cow disease in humans. So knowledge of EGCG's effect on 67 LR might have implications in the treatment of these diseases.[4]

According to the U.S. National Cancer Institute, in laboratory studies using animals, catechins inactivated oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells[citation needed].

White tea has been claimed to be even more effective, based upon preliminary work by Santana-Rios et al.[5]

[edit] Increases metabolic rate

Clinical trials conducted by the University of Geneva in Switzerland indicate that green tea raises metabolic rates and speeds up fat oxidation. In addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are burned), and hence increases energy expenditure.[citation needed]

There is also a suggestion that it can increase endurance in exercise by improving fat metabolism[6]

[edit] Possible anti-diabetes effect

There is also epidemiological evidence that drinking green tea (but not black tea or oolong tea) may help prevent diabetes,[7] although it is worth noting that this is evidence of an association, and that future studies are needed to confirm the effect.

[edit] Boosts immune system and mental alertness

On 21 April 2003 the Brigham and Women's Hospital released details of a research project which indicated that the amino acid L-theanine may help the body's immune system response when fighting infection, by boosting the disease-fighting capacity of gamma delta T cells. The study included a four-week trial with 11 coffee drinkers and 10 tea drinkers, who consumed 600ml of coffee or black tea daily. Blood sample analysis found that the production of anti-bacterial proteins was up to five times higher in the tea-drinkers, an indicator of a stronger immune response.[8]

L-theanine has also been found to increase alpha wave production in the brain, which is associated with a state of "alert relaxation".[9]

[edit] Lowers chances of cognitive impairment

A 2006 study[10][11] showed that elderly Japanese people who consumed more than 2 cups of green tea a day had a 50 percent lower chance of having cognitive impairment, in comparison to those who drank fewer than 2 cups a day, or who consumed other tested beverages.

[edit] Lowers stress hormone levels

According to a study by UCL researchers published in the journal Psychopharmacology, drinking black tea has an effect on stress hormone levels in the body and thus helps in recovering more quickly from life's stresses. The study showed that, 50 minutes after a high stress event, subjects who drank 4 cups of black tea per day for a 4 week period experienced an average cortisol drop of 47%, compared to 27% for the placebo group. Blood platelet activation, which is linked to blood clotting and the risk of heart attacks was also lower in the tea drinker's group.[12]

[edit] Effects on HIV

A recent study appearing in the Journal of Allergy and Clinical Immunology stated that epigallocatechin gallate (EGCG) found in Green Tea can help to boost one's immune system, therefore helping to prevent HIV. University of Sheffield Research Professor Mike Williamson stated that, "Our research shows that drinking green tea could reduce the risk of becoming infected by HIV, and could also slow down the spread of HIV" however was quick to point out that, "It is not a cure, and nor is it a safe way to avoid infection, however, we suggest that it should be used in combination with conventional medicines to improve quality of life for those infected" as well as the fact that the research is in very early stages.[13]

[edit] Effects associated with caffeine

Main article: Caffeine.

A cup of green tea contains between 15 and 50 mg of caffeine. Certain cognitive benefits are associated with caffeine consumption, such as a reduction in the likelihood of Parkinson's disease and a temporary increase in short term memory. However, caffeine is addictive and overuse can result in harmful side-effects such as an increased likelihood of sleep disorder.

[edit] United States FDA

In a July 2005 review of claims made about the health benefits of green tea, the U.S. Food and Drug Administration concluded that it was highly unlikely that green tea reduces the risk of breast and prostate cancer. The FDA believes that the evidence does not support qualified health claims for green tea consumption and a reduced risk of cancer.[14]

[edit] Effect of milk on tea

A study[15] at the Charité Hospital at the University of Berlin in Mitte showed that adding milk to tea will block the normal, healthful effects that tea has in protecting against cardiovascular disease. It was claimed to do this because casein from the milk binds to the molecules in tea that cause the arteries to relax, especially a catechin molecule called EGCG. One of the researchers told New Scientist magazine that "It probably also blocks tea's effect on other things, such as cancer.".[16] Other studies have found little to no effect from milk on the observed increase in total plasma antioxidant activity. [17] Teas with high EGCG content, such as green tea, are not typically consumed with milk. Previous studies have observed a beneficial effect from black tea which was not attributable to the catechin content.[18] Plant-based "milks", such as soy milk, do not contain casein and are not known to have similar effects on tea.

[edit] External links

[edit] References

  1. ^ N. H. Woodward, Teas of the World (1980), as cited in D. A. Balentine, M. E. Harbowy, H. N. Graham, Tea: The Plant and Its Manufacture; Chemistry and Consumption of the Beverage in Caffeine ed G. Spiller (1998)
  2. ^ Green Tea: from the University of Maryland Medical Center Alternative/Complementary Medicine library
  3. ^ New Scientist,20 March 2004
  4. ^ Structural and Molecular Biology, DOI:10.1038/nsmb743
  5. ^ Santana Rios, G.; Orner, G. A.; Amantana, A.; Provost, C.; Wu, S-Y.; Dashwood, R. H.; Potent antimutagenic activity of white tea in comparison with green tea in the Salmonella assay Mutation Research, 495 61-74 (2001)
  6. ^ Takatoshi Murase, Satoshi Haramizu, Akira Shimotoyodome, Ichiro Tokimitsu, and Tadashi Hase Green tea extract improves running endurance in mice by stimulating lipid utilization during exercise Am J Physiol Regul Integr Comp Physiol 290: R1550-R1556, 2006. [1]
  7. ^ Iso H et al. (2006). "The Relationship between Green Tea and Total Caffeine Intake and Risk for Self-Reported Type 2 Diabetes among Japanese Adults" 144 (8): 554–62. 
  8. ^ Drinking Tea May Boost Immune System
  9. ^ Juneja, LR, Chu, DC, Okubo, T, Nagato, Y, & Yokogoshi, H. (1999). L-Theanine - a unique amino acid of green tea and its relaxation effect in humans. Italic textTrends in Food Science & TechnologyItalic text, 10(2), 199-204.
  10. ^ "The American Journal of Clinical Nutrition" (Vol. 83, pp.355-361).
  11. ^ Green tea could protect against Alzheimer’s
  12. ^ Black tea soothes away stress
  13. ^ Green tea 'may keep HIV at bay'
  14. ^ FDA Issues Information for Consumers about Claims for Green Tea and Certain Cancers
  15. ^ Lorenz, M et al., "Addition of milk prevents vascular protective effects of tea", European Heart Journal (DOI: 10.1093/eurheartj/ehl442)
  16. ^ Milk wrecks the health benefits of tea, New Scientist, 09 January 2007
  17. ^ Vijayakumar C. Reddy, G.V. Vidya Sagar, D. Sreeramulu, L. Venu, M. Raghunath, Addition of Milk Does Not Alter the Antioxidant Activity of Black Tea, Annals of Nutrition and Metabolism 2005;49:189-195 PMID 16020939 [2]
  18. ^ Widlansky ME, Duffy SJ, Hamburg NM, Gokce N, Warden BA, Wiseman S, Keaney JF Jr, Frei B, Vita JA. Effects of black tea consumption on plasma catechins and markers of oxidative stress and inflammation in patients with coronary artery disease. Free Radic Biol Med. 2005 February 15;38(4):499-506. PMID 15649652
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