The February 2006 issue of the American Journal of Clinical Nutrition published the finding of researchers at Tohoku University Graduate School of Medicine in Sendai, Japan, that consuming more green tea is associated with a lower prevalence of cognitive impairment. To the researchers' knowledge, the study is the first to examine the association between green tea drinking and cognitive function in humans.

Shinichi Kuriyama, of the school's departments of public health and forensic medicine, and colleagues evaluated data from 1002 men and women aged 70 and older who participated in the Japanese Comprehensive Geriatric Assessment in 2002. Subjects completed questionnaires concerning the frequency of green tea, black tea, and coffee consumption among other questions. Cognitive function test scores were used to classify the participants as having no impairment, slight cognitive impairment, cognitive impairment, or severe cognitive impairment.

High consumption of green tea at two or more cups per day by the top one-third of participants was associated with less than half the incidence of cognitive impairment, including severe cognitive impairment, than that found among participants whose intake was in lowest third at three or fewer cups per week. Participants whose tea consumption was in the middle third experienced a 38 percent reduction. No significant relationship between black tea or coffee consumption and cognitive impairment was observed.

The authors suggest that the lower prevalence of dementia and Alzheimer's disease in Japan could be explained by the green tea consumed by this population. "Given the high prevalence, worldwide rapid increase, and clinical significance of dementia," they write, "any association between the intake of green tea, a drink with little toxicity and no calorific value, and cognitive function could have considerable clinical and public health relevance."

—D Dye

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