Consumption of Green and Black Tea Is Associated With a Lower Risk of Stroke

SAN DIEGO—Consuming at least three cups of green or black tea per day is associated with a reduced risk of ischemic stroke and mortality from stroke, despite differences in tea-drinking customs and stroke mortality rates across various countries, reported Lenore Arab, PhD, at the 2009 International Stroke Conference. Previous research conducted by Dr. Arab and colleagues, at the University of North Carolina, showed a moderately protective effect of tea consumption in the case of myocardial infarction. However, the results were heterogeneous across the United States and the United Kingdom, and the evidence existed only for populations drinking black tea.

Since then, new data have been reported, said Dr. Arab, Professor of Medicine and Adjunct Professor of Biological Chemistry at the David Geffen School of Medicine, University of California, Los Angeles. Thus far, nine preclinical trials, as well as five epidemiologic studies, have been published in peer review journals. Studies in rats, mice, and gerbils have shown reduced infarct volume (40% to 80%), increased surviving neurons, and delayed stroke onset following administration of green tea extract, green tea catechins, and other components of tea, such as epigallocathechin gallate, theaflavin, or theanine.

To determine whether consumption of green or black tea as an infused hot beverage had an impact on the risk of stroke in humans, Dr. Arab and colleagues conducted a meta-analysis of clinical trials and observational epidemiologic studies. The results were also published in the February 19 online edition of Stroke. The researchers searched the PubMed and Web of Science databases for the following search terms: tea, green tea, black tea, flavonoids, Camelia sinensis, stroke, subarachnoid hemorrhage, ischemic stroke, and hemorrhagic stroke. Between-study heterogeneity was assessed using forest plotting and the Hedge’s Q test.

“Ten studies were identified that could provide original data on either fatal or nonfatal ischemic stroke in relationship to tea consumption,” said Dr. Arab. “This resulted in 4,300 strokes and approximately 195,000 individuals.”

Dr. Arab’s team found that “the additional consumption of three cups of tea per day is associated with an average 21% lower risk of ischemic stroke.” No heterogeneity was observed across the studies, which were conducted in China, Japan, Finland, the Netherlands, Australia, and the United States.

Subanalyses showed that “the strong association of tea consumption with reduced risk could not be attributed to an effect in Asians more than non-Asians and green tea consumers more than black tea consumers,” the researchers wrote.

Dr. Arab suggested several mechanisms or pathways that might explain the relationship between tea consumption and stroke. One theory may be that neuronal health is enhanced by tea consumption prior to the ischemic event. Another explanation is that glutamate inhibition by theanine might reduce stroke damage to neurons.

“These findings suggest that tea drinking may be one of the most actionable lifestyle changes to significantly reduce the risk of stroke,” Dr. Arab and colleagues concluded.

NR