Green tea consumption is associated with lower incidence of mild cognitive impairment and dementia in elderly people
Mitigating effects of dietary habits, including drinking of tea or coffee, on cognitive decline (and even dementias) in aging is a research topic with potentially very high societal impact. While coffee and tea do contain large amounts of polyphenols and caffeine that have potential neuroprotective effects, previous studies on the relationships between coffee and tea consumption and dementia seem to have produced mixed results. In their recent population-based longitudial study, Dr Moeko Noguchi-Shinohara et al. (2014) inspected the relationships between coffee, black tea, and green tea consumption and incidence of dementia and mild cognitive impairment.
Out of a total of 2845 residents aged >60 years in 2007 in Nakajima, Japan, 723 individuals meeting criteria for inclusion voluntarily participated in the study. Cognitive level was tested using mini-mental state examination and clinical dementia rating scales. Health surveys and blood tests were also carried out to control for some of the potentially intervening variables such as ApoE phenotype status and diabetes. Consumption of coffee, black tea, and green tea was recorded and divided into three classes for the purposes of data analysis: zero consumption, 1-6 days/week, and every day. At the time of follow-up testing conducted on the average 4.9 years later, it was observed that frequent consumption of green tea (but neither black tea nor coffee) was associated with significantly lower incidence of dementia and mild cognitive impairment.
The authors propose that these interesting findings could be due to a number of factors. One of the possible mechanisms that they bring up is that, unlike black tea, green tea contains catechins, especially epigallo catechin 3-gallate, as well as myricetin, which both have been described to have neuroprotective effects. The authors further remind that higher physical activity and number of hobbies also correlated with green tea consumption, although the beneficial effects of green tea prevailed even when these factors were taken into account in the analysis. Taken together, these findings add to the pool of evidence suggesting that green tea might have some neuroprotective effects that help guard against aging-related cognitive decline.
Reference: Noguchi-Shinohara M, Yuki S, Dohmoto C, Ikeda Y, Samuraki M, Iwasa K, Yokogawa M, Asai K, Komai K, Nakumura H, Yamada M. Consumption of green tea, but not black tea or coffee, is associated with reduced risk of cognitive decline. PLoS ONE (2014) 9: e96013. http://dx.doi.org/10.1371/journal.pone.0096013