Green Tea Reduces Mortality Due to Cardiovascular Disease—Most Notable in Women
Green Tea Reduces Mortality Due to Cardiovascular Disease—Most Notable in Women
By Donald Brown, ND, Dr. Brown is Founder and Director, Natural Product Research Consultants, Inc.; serves on the Advisory Board of the American Botanical Council and the President's Advisory Board, Bastyr University, Seattle, WA; and is an Advisor to the Office of Dietary Supplements at the National Institutes of Health; he is a consultant for Nature's Way, Inc.
Source: Kuriyama S, et al. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: The Ohsaki study. JAMA 2006;296:1255-1265.
Abstract: In a population-based, prospective study (The Ohsaki National Health Insurance Cohort Study), Japanese adults were studied for a possible association between green tea consumption and all-cause and cause-specific mortality. The study included 40,530 Japanese adults (aged 40-79 years) with no history of stroke, coronary heart disease, or cancer at baseline. Participants were followed for up to 11 years (1995-2005) for all-cause mortality and for up to seven years (1995-2001) for cause-specific mortality (e.g., cardiovascular disease, cancer). The primary outcome measures were mortality due to cardiovascular disease, cancer, and all causes. A self-administered questionnaire included items on dietary intake (a 40-item food frequency questionnaire). Among the items was frequency of recent average consumption of four beverages (green tea, oolong tea, black tea, and coffee). The frequency of green tea consumption was divided into five categories: never, occasional, 1-2 cups/d, 3-4 cups/d, and 5 or more cups/d. Within the study region, the volume of a typical cup of green tea is 100 mL.
Over the 11 years of follow-up (follow-up rate, 86.1%), 4,209 participants died. Over the seven years of follow-up (follow-up rate of 89.6%), 892 participants died of cardiovascular disease and 1,134 participants died of cancer. Green tea consumption was inversely associated with mortality due to all causes and due to cardiovascular disease. The inverse correlation for all-cause mortality was greater in women (P = 0.03 for interaction with sex). In men, the multivariate hazard ratios of mortality due to all causes associated with different green tea consumption frequencies were 1.00 (reference) for less than 1 cup/d, 0.93 (95% confidence interval [CI] 0.83-1.05) for 1-2 cups/day, 0.95 (95% CI 0.85-1.06) for 3-4 cups/d, and 0.88 (95% CI 0.79-0.98) for 5 or more cups/d (P = 0.03 for trend). The data for women were 1.00, 0.98 (95% CI 0.84-1.15), 0.82 (95% CI 0.70-0.95), and 0.77 (95% CI 0.67-0.89), respectively (P < 0.001 for trend).
The inverse correlation was greater for cardiovascular disease mortality than all-cause mortality and this was most notable in women. In women the multivariate hazard ratios of cardiovascular disease mortality across increasing green tea consumption were 1.00, 0.84 (95% CI 0.63-1.12), 0.69 (95% CI 0.52-0.93), and 0.69 (95% CI 0.53-0.90), respectively (P = 0.004 for trend). Among the types of cardiovascular disease mortality, the greatest inverse correlation was noted for stroke mortality. The hazard ratios of cancer mortality were not significantly different from 1.00 in all green tea categories compared with the lowest-consumption category and did not differ by sex.
Comments
As opposed to our coffee-fueled culture (broadcasting here from the home of Starbucks), tea is the most consumed beverage in the world aside from water with 3 billion kg of tea produced each year worldwide. This fascinating population-based, prospective study suggests that the more green tea consumed daily, the greater your chances of staying alive—especially if you're a woman. Compared with participants who consumed less than 1 cup of green tea per day, those who consumed 5 or more cups per day had a risk of all-cause and cardiovascular disease mortality that was 16% lower (during 11 years of follow-up) and 26% lower (during seven years of follow-up), respectively. It should be noted that smoking was greater among males in this study and may explain some of the decreased significance in green tea protection when compared to females. This is the largest study to date to show this remarkable correlation with decreased risk of cardiovascular disease and the results support those found in earlier population studies.1,2 However, one earlier population trial found an inverse correlation between green tea and cancer mortality when considering both men and women;2 this study failed to show a correlation.
When considering studies that have focused only on women, the news of the chemopreventive effects of tea is far more compelling. A 2006 study published in Archives of Internal Medicine reported an inverse correlation between green tea consumption and risk of ovarian cancer in 61,057 Swedish women followed for up to 17 years.3 As was the case with the JAMA study reviewed above, this effect was dose-dependent with those women consuming two or more cups of green tea per day having the lowest incidence of ovarian cancer. Another study found that increased consumption of green tea post-diagnosis improved the survival of Chinese women with epithelial ovarian cancer.4
The data on protection against breast cancer and breast cancer recurrence are equally impressive. In a case-control study in Los Angeles County focused on Asian-American women, an inverse correlation was found between green tea consumption and risk of breast cancer.5 Another study found that consumption of 5 or more cups of green tea per day prior to cancer diagnosis was associated with a decreased risk of recurrence in Japanese women with stage I and II breast cancer.6 No improvement in prognosis was noted for women with stage III breast cancer.
Conclusion: It may be safe to assume that we should be telling our female patients to switch out a few of those lattes for green tea. Large population studies suggest that risk of cardiovascular disease, ovarian cancer, and breast cancer in women are all reduced with increased intake of green tea. Caffeine-free versions are widely available for those persons sensitive to caffeine. Finally, it's important to remember that these studies were conducted with populations consuming green tea as a beverage and not in capsules. Recent case studies suggesting a possible link between encapsulated green tea extracts and hepatotoxicity suggest more careful analysis of these products before recommending them as a tea substitute.7
References
1. Sato Y, et al. Possible contribution of green tea drinking habits to the prevention of stroke. Tohoku J Exp Med 1989;157:337-343.
2. Nakachi K, et al. Preventive effects of drinking green tea on cancer and cardiovascular disease: Epidemiological evidence for multiple targeting prevention. Biofactors 2000;13:49-54.
3. Larsson SC, Wolk A. Tea consumption and ovarian cancer risk in a population-based cohort. Arch Intern Med 2005;165:2683-2686.
4. Zhang M, et al. Green tea consumption enhances survival of epithelial ovarian cancer. Int J Cancer 2004;112:465-469.
5. Wu AH, et al. Green tea and risk of breast cancer in Asian Americans. Int J Cancer 2003;106;574-579.
6. Nakachi K, et al. Influence of drinking green tea on breast cancer malignancy among Japanese patients. Jpn J Cancer Res 1998;89:254-261.
7. Bonkovsky HL. Hepatotoxicity associated with supplements containing Chinese green tea (Camellia sinensis). Ann Intern Med 2006;144:68-71.
Brown D. Green tea reduces mortality due to cardiovascular disease—most notable in women. Altern Ther Women's Health 2007;9(2):13-14.Subscribe Now for Access
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