First, a little background. 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, specifically catechins and flavonoids. Phytochemicals are substances that have been proposed to have health benefits over and above what the vitamins or minerals provide. Phyto is the Greek word for plants. Phytochemicals often have strange names (hard to pronounce, so bear with me.)
The active phytochemical in teas is called 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 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 after 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 beverage in the diet of mice could suppress colon cancer. 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. Generally 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.
Black and green tea consumption and the risk of coronary artery disease: a meta-analysisZe-Mu Wang, Bo Zhou, Yong-Sheng Wang, Qing-Yue Gong, Qi-Ming Wang, Jian-Jun Yan, Wei Gao, and Lian-Sheng WangConclusions: 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 through the link provided) 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 that can lead to anemia.
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. Everyone can benefit from any tea. It has the potential to offer powerful antioxidant protection, reduce blood sugar, is anti-inflammatory, and lowers cholesterol. For a common little beverage that costs next to nothing – that’s a pretty powerful resume.