Tea is currently the most consumed beverage in the world besides water. Americans consume an average of 153 cups a year. Most Americans drink black tea while green tea is becoming more popular as claims are made about its health benefits more than likely from phytochemicals called polyphenols, mainly catechins and flavonoids.
A bioactive compound is provided by epigallocatechin -3 galate (EGCG) found in green tea. Green tea is produced from the withered leaves and buds of Cameillia sinensis by heating or steaming before drying.
Bottled tea is not equivalent to brewed tea in terms of polyphenol content. While all teas (not herbal) contain between 100-300 mg of flavonoids per serving, bottled teas (16 oz.) contain fewer polyphenols than one cup of brewed tea.
From anecdotal evidence, epidemiological and experimental models, tea is thought to have cancer preventive effects. A prospective study of a group of Japanese people younger than 79 years old with a 13-year follow-up indicated a delay of cancer onset and cancer-related death, as well as all-cause mortality with an increased consumption of green tea. Another cohort of 8,552 general residents of Japan presented evidence for preventive effects of drinking green tea on both cancer and heart disease. In one animal study, researchers showed that green tea as a main source of fluid in the diet of mice could suppress colon carcinogenesis. Another study suggested a reduction of chronic inflammation by green tea which may be associated with cancer and heart disease.
There are few human studies on green tea. Cancer risk is reduced more in those people who consume green tea than black tea since the polyphenols in black tea are not absorbed as well. Studies show that the amount of tea consumed effects cancer prevention effects – i.e. the range has been from two to three cups of green tea per day to 10 cups per day. The FDA has denied a request from a tea company to display a health benefit of cancer prevention on their labels. The FDA concluded, “there is no credible evidence to support qualified health claims for green tea consumption and a reduced risk of gastric, lung, colon/rectal, esophagus, pancreatic, ovarian and combined cancers.”
Black and green tea consumption and the risk of coronary artery disease: a meta-analysis1,2,3
. Ze-Mu Wang, Bo Zhou, Yong-Sheng Wang, Qing-Yue Gong, Qi-Ming Wang, Jian-Jun Yan, Wei Gao, and Lian-Sheng Wang
Background: Epidemiologic studies are inconsistent regarding the association between tea consumption and the risk of coronary artery disease (CAD).
Objective: The objective was to perform a meta-analysis to determine whether an association exists between tea consumption and total CAD endpoints in observational studies.
Design: We searched PUBMED and EMBASE databases for studies conducted from 1966 through November 2009. Study-specific risk estimates were combined by using a random-effects model.
Results: A total of 18 studies were included in the meta-analysis: 13 studies on black tea and 5 studies on green tea. For black tea, no significant association was found through the meta-analysis [highest compared with lowest, summary relative risk (RR): 0.92; 95% CI: 0.82, 1.04; an increment of 1 cup/d, summary RR: 0.98; 95% CI: 0.94, 1.02]. For green tea, the summary RR indicated a significant association between the highest green tea consumption and reduced risk of CAD (summary RR: 0.72; 95% CI: 0.58, 0.89). Furthermore, an increase in green tea consumption of 1 cup/d was associated with a 10% decrease in the risk of developing CAD (summary RR: 0.90; 95% CI: 0.82, 0.99).
Conclusions: Our data do not support a protective role of black tea against CAD. The limited data available on green tea support a tentative association of green tea consumption with a reduced risk of CAD. However, additional studies are needed to make a convincing case for this association.
It appears from a meta-analysis (see abstract above) of studies on black and green tea that there was no association with black tea and coronary artery disease; however, green tea did show a tentative association. There are few studies on green tea; more are needed.
However, another meta-analysis reported that either green or black tea (3 or more cups) reduced ischemic stroke risk by 21%. (Stroke, 2009; 40:1786-1792.)
Green tea extracts are often found in the weight loss sections of health food stores and supermarkets. I could only find one or two studies on humans from reputable journals. Most of the studies were animal studies. The studies are inconclusive and inconsistent. Don’t believe the hype that green tea will burn fat.
What is the Bottom Line?
If you’re looking for dramatic health benefits from tea – the evidence is not yet there. As with most nutrition studies, there are mixed results. The problem may be that tea consumption is variable as far as amounts of cups consumed. Some bottled teas have added sugar; some people add sugar to brewed tea; some add milk. Most epidemiological studies are based on recall or observation, which is always a problem in these types of studies. One drawback of overconsumption is that the polyphenols in tea interfere with nonheme iron absorption.
Tea has been around for the last 2,000 years and is the beverage of choice of many Asian countries. There is no reason to not enjoy it. If you have not tried green tea, do so. It may take a while to get used to it; however, it may be the best bet for health.