Japanese Tea and Heart Health Risk Reduction: The Ohsaki Study
A landmark study conducted in Japan called the “Ohsaki Study” also published in the New England Journal of Medicine (the most well-respected, peer-reviewed medical journal) as well as the Journal of the American Medical Association (full article linked here) has highlighted the significant health benefits of green tea consumption, particularly concerning cardiovascular disease, and overall mortality rates in Japan. The findings are impressive and support the regular consumption of fresh Japanese green tea as a meaningful way to reduce risk of death from any cause, especially from heart disease or stroke.
Study Overview
The Ohsaki Study, a large-scale, population prospective cohort study (looking at a population and following them over time while analyzing tea drinking habits), examined the relationship between green tea intake and death outcomes among Japanese adults. Researchers followed over 40,000 participants over a period of up to 11 years, collecting data on their green tea consumption habits and subsequent health outcomes.
Key Findings
Drinking 5 or more cups of green tea daily was linked to a 16% lower risk of all-cause mortality (death from any cause) in men and a 26% lower risk in women.
The risk of cardiovascular death (i.e. death from heart attack or stroke) was reduced by 31% in women and 22% in men in the highest green tea consumption group.
Dose-Response Relationship: The study found a dose-response relationship, indicating that higher levels of green tea consumption were associated with greater reductions in mortality risk.
Gender Differences: The protective effects of green tea consumption were more pronounced in women than in men, suggesting potential gender-specific health benefits.
Cancer mortality showed a modest reduction but was not statistically significant.
Implications
These findings support the incorporation of green tea into daily dietary habits as a simple and accessible strategy to enhance health and longevity. The underlying mechanism for this significant impact on longeity is still yet to be further studied but thought to be related to multiple factors. Green tea polyphenols, a class of naturally occurring plant compounds known for their antioxidant properties, particularly (-)-epigallocatechin-3-gallate found in Japanese green tea, may play an important role. These compounds help to reduce inflammation and oxidative stress encountered by the body. The study also noted that green tea consumption reduced risk of ischemic stroke (stroke caused by plaque buildup and blockage of arteries in the brain) but not affecting hemorrhagic stroke (stroke due to a burst blood vessel, such as with high blood pressure) which suggests that green tea polyphenols may help to reduce or reverse plaque buildup itself.
Weak or no relationships were observed between black tea or oolong tea and death which further suggests that fresh green tea is rich in these important compounds not found in other types of tea.
Conclusion
Incorporating green tea into one's daily routine may offer a modest yet beneficial impact on health, particularly in reducing the risk of chronic diseases and extending lifespan. As always, it's essential to consider green tea consumption as part of a balanced diet and healthy lifestyle. In Japan, this regularly includes a diet full of soy products (soybeans, tofu), fermented foods (miso, picked vegetables), fruits and vegetables, with lean proteins and regular consumption of tea.
