Tea is the most widely consumed beverage in the world, not to mention one of the world’s healthiest beverages. Now an observational study of nearly 14,000 Japanese older adults has found that green tea could keep you doing the things you enjoy well into old age.
Researchers from Tohoku University Graduate School of Medicine found an association between consumption of 5 cups of green tea daily and a reduced risk of functional disability—likely attributed, the researchers remind, to green tea’s favorable effects on the heart, bones, the brain, and the body as a whole.
When it comes to heightened health, green tea appears to be the beverage of choice. The researchers, who published their findings in the American Journal of Clinical Nutrition, wrote, “In contrast to green tea, we observed no association between black tea, oolong tea, or coffee consumption and incident functional disability.”
To bolster validity of the findings, the researchers controlled for diseases, alcohol consumption, education, smoking status, body mass, exercise, community involvement, and specific dietary components (such as fish, oolong tea, black tea, and coffee).
In Japan, a nationally uniform questionnaire is used to assess functional disability in the elderly. Put simply, functional disability is an assessment of an individual’s inability to perform activities of daily living (ADL). For the purposes of this study, Level 2 functional disability, or required assistance for at least one basic ADL task, is the marker for determining individuals with disability.
For three years, the study followed survey data about green tea consumption and national data reporting functional disability in 13,988 respondents ages 65 or older. Frequency of green tea consumption was divided between one or two cups per day, three to four cups per day, and five cups per day. Consumers of more than five cups of green tea reported more positive lifestyle factors—such as higher protein consumption, social support, and better cognition—however, when lifestyle factors were removed, the isolated benefits of green tea remained significant.
The authors noted that there are “significant dose-response associations between green tea consumption and incident functional disability” in spite of all controlled variables. The greatest cause of functional disability was reported to be frailty—usually relating to lack of muscle strength. This may be an area where green tea can help too, as recently, according to researchers, “green tea polyphenols have been reported to improve leg strength.”
Polyphenols, the bioactive molecules that reside in the green tea leaves, may be the key to improving health well into the lifespan. In contrast to the black and the oolong teas that were also assessed, green tea contains large amounts of polyphenols such as epigallocatechin gallate (EGCG). EGCG has demonstrated protection of DNA from oxidative stress. The antioxidants native to green tea are the most likely cause for overall health promotion.
The researchers state that the strength of the results is bolstered by multiple factors: the accuracy of the disability survey, the large sample population, the high follow-up rate, and the large variety of factors taken into account. However, they report, one limitation may be that they did not control for income or socioeconomic status. More research and clinical trials are necessary to confirm the inverse association between green tea consumption and functional disability.
Reference: Tomata Y et al. Green tea consumption and the risk of incident functional disability in elderly Japanese: the Ohsaki Cohort 2006 Study. Am J Clin Nutr; doi: 10.3945/ajcn.111.023200.