Green tea has been extensively researched, and evidence suggests that it may reduce the risk of cardiovascular disease, osteoporosis and cognitive dysfunction. Epidemiological studies and clinical trials suggest that green tea is protective of disease due to its high content of antioxidants, that may decrease oxidative stress in humans. Much of the interest regarding green tea originated in Japan, where consumption amongst the general population is higher than black tea. Because of its broad health effects, particularly against debilitating conditions such as stroke, dementia and osteoporosis, researchers are interested in the general health effects of green tea in the elderly, in terms of preventing functional impairment. Such disability can arise following a stroke, a fall due to osteoporosis or because of dementia. Therefore because green tea reduces the risk of these conditions, it may reduce the disability associated with them.
Researchers1 investigated the association between green tea consumption and functional impairment using a prospective cohort study of 13,988 Japanese individuals aged >65 years. Green tea consumption was estimated from dietary records in the Ohsaki Cohort 2006 Study, and the infirmity outcome was retrieved from medical records. Using regression analysis, the researchers showed that functional disability occurred in 9.4 % of subjects. Amongst those subjects who consumed 1-2 cups of green tea per day, the hazard ratio for functional disability was 0.9, but the hazard ratio dropped to 0.75 with consumption of 3-4 cups of green tea per day, and to 0.67 with consumption of over 5 cups per day, when compared to those who consumed less than 1 cup per day. Adjustment for confounding variables did not remove the significance of the results and exclusion of subjects who were impaired functionally early in the study, agued against reverse causality.
These results suggest that up to 5 cups of green tea per day may be beneficial as consumption is associated with a reduced risk of developing functional impairment. This is supportive of the data that shows a beneficial effect for green tea consumption against osteoporosis, stroke and cognitive impairment, all major causes of disability. Analysis of the oolong tea, black tea and coffee consumption showed no association with functional impairment, suggesting that neither caffeine nor the water content was responsible for the correlation. This suggests that the polyphenol content of green tea, which is comprised of high concentrations of the flavan-3-ol epigallocatechin gallate (EGCG), may be responsible for the protective effects of green tea on functional impairment. Interestingly, the authors also found that green tea consumption was associated with improved cognitive activity, which supports research showing protective effects of tea against Parkinson’s disease.
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