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
