Green Tea

As astute university students, all of us were expected to major in a chosen field and have a Minor in coffee-drinking. The latter, I struggle with even to this day.

I actually used to drink a cup of coffee daily during my high school days. It was usually milk with coffee, and it got me up every morning. During the later part of university however, I started shifting from coffee to tea as I noticed that even that half a cup of coffee gives me tremors lasting most of the day and also the frequent acid reflux. And so I have been a tea-drinker since, preferring a cup of tea or even plain hot water whenever offered coffee. (I do tolerate the occasional coffee-flavored dessert, however.)

Unlike coffee, which to me seemed to have far more adverse consequences than its purported benefits, tea has always had a calming effect, for some reason. Perhaps it is because of the lower caffeine content? Caffeine or otherwise, many others have extolled the virtues of tea, especially green teas. Many of these virtues have indeed been anecdotal, but there have as well been many studies scrutinizing the health benefits of teas and tea-derived products.

The beneficial effects of green tea (which I personally prefer for its ‘sweet’ and sometimes fruity flavor in contrast to other teas) has been attributed to the type of polyphenol compounds called catechins. (Polyphenols happen to be the same class of compounds credited for the beneficial effects of other foodstuffs like red wine, cocoa, etc.) The most important and most abundant catechin found in green tea is said to be epigallocatechin-3-gallate (EGCG).

Catechins, like EGCG, are abundant in green tea as the leaves are processed (steamed and dried) fresh. Black teas, on the other hand, are fermented: the leaves are crushed, releasing enzymes that polymerize catechins and transform them into a different class of polyphenols known as thearubigins that give the black and oolong teas its distinct flavor and color.

The physiologic effects of catechins, EGCG foremost, span the spectrum of acting as an antioxidant, antimicrobial, anti-cancer, neuroprotective, cardioprotective, and even as an aid to reduce fat and blood glucose.

Many studies have attempted to confirm any or all of these claims. In one community-based study conducted in Japan [5], researchers found that consumption of green tea correlates with better cognitive function in old age. In the study, a cross-sectional survey, respondents who drank two or more cups of green tea fared better in the Mini Mental State Exam than those who drank less green tea, black/ oolong tea, or coffee. The researchers theorized that possibly, EGCG had an adverse effect on the protein contributing to the development of neuritic plaques (hallmark of Alzheimer’s Disease). The study also noted the benefits of green tea, albeit for rats with Parkinson's Diesease.

Various other papers have cited animal studies that have shown that catechins can lower lipid levels (triglycerides and total cholesterol), and inhibit fat accumulation. One such study, that of Nagao, et al [3] concluded that ingestion of catechin-rich products may have a role in the treatment and prevention of obesity. The UK study by Venables, et al [9], on the other hand concluded that ingestion of green tea extracts in the short term can improve glucose tolerance among other things.

Polyphenols are also being studied as anti-cancer agents. Many studies have put forward theories that compounds like catechins exert adverse effects on the growth of tumor cells by interfering with their chemical messengers [1]. But cancer, and its many types has a complex set of factors to rely on for growth. This has complicated drawing conclusions from many surveys done on the correlation between the disease and tea consumption. One study in Japan have found no relation between high green tea intake and the incidence of gastric cancer [8]. The researchers theorized the presence of other factors such as consumption of preserved foods (known to be carcinogenic). Another doctor put forward the theory that the protective effect of green tea can only be seen if consumed at certain quantities (>/= 2 liters) [4].



Indeed, many of the anecdotal claims about the benefits of (green) tea consumption have been validated or disproven by these (preliminary) studies. Many of the studies mentioned had small sample populations, hence much has still to be established by larger surveys and trials about the physiologic effects of catechin-rich food or supplement consumption. Further the minimum dose of catechins with the desired effect has yet to be established. Debates are still on going.



For now however, I will continue to sip on my green tea.

REFERENCES:
[1] Ebeler SE, Brenneman CA, Kim GS, et al. Dietary catechin delays tumor onset in a transgenic mouse model. Am J Clin Nutr. 2002; 76:865-872. [link]

[2] Henning SM, Niu Y, Lee NH, Thames GD, Minutti RR, Wang H, Go VL, Heber D. Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement. Am J Clin Nutr. 2004;80:1558–64. [link]

[3] Nagao T, Komine Y, Soga S, et al. Ingestion of a tea rich in catechins leads to a reduction in body fat and malondialdehyde-modified LDL in men. Am J Clin Nutr. 2005;81:122-129. [link]

[4] Kono S. Green tea and gastric cancer in Japan. N Engl J Med. 2001; 344: 1867-1868. [link]

[5] Kuriyama S., Hozawa A., Ohmori K., Shimazu T., Matsui T., Ebihara S., Awata S., Nagatomi R., Arai H., Tsuji I. Green tea consumption and cognitive function: a cross-sectional study from the Tsurugaya Project 1. Am J Clin Nutr. 2006; 83:355–361. [link]


[6] Manach C, Scalbert A, Morand C, Remesy C, Jimenez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr. 2004; 79:727-747. [link]

[7] Sano T, Sasako M. Green tea and gastric cancer. N Engl J Med 2001;344:675–676. [link]

[8] Tsubono Y, Nishino Y, Komatsu S, et al. Green tea and the risk of gastric cancer in Japan. N Engl J Med 2001;344:632-636. [link]

[9] Venables MC, Hulston CJ, Cox HR, Jeukendrup AE. Green tea extract ingestion, fat oxidation and glucose tolerance in healthy humans. Am J Clin Nutr. 2008; 87:778-784. [link]

[10] Yang CS, Landau JM. Effects of tea consumption on nutrition and health. J Nutr. 2000; 130:2409-2412. [link]