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The results of a meta-analysis published in the May 1, 2009 issue of the American Heart Association journal Stroke
revealed that men and women who consumed at least three cups of green
or black tea per day had a lower risk of stroke than those who consumed
less than one cup.
For
their review, Lenore Arab, PhD and her colleagues at UCLA's David
Geffen School of Medicine selected 9 epidemiological studies that
included data on tea intake and fatal or nonfatal stroke outcomes. The
studies included a total of 194,965 participants in 6 different
countries, among whom 4,378 strokes occurred.
The
pooled analysis uncovered a 21 percent lower risk of fatal or nonfatal
stroke among those who consumed three or more cups of tea per day
compared to those whose intake was reported at less than one cup per
day. The findings involved participants from diverse geographical areas
and were consistent whether green or black tea was consumed.
Although
the analysis did not break down stroke according to type, the authors
believe that the association observed is likely to be due primarily to
tea's effect on ischemic stroke. In their discussion of possible
mechanisms for tea against stroke, they note that although tea's
antioxidant and anti-inflammatory actions are frequently cited, green
and black tea have also been demonstrated to reduce blood pressure in
an experimental model of hypertension, a condition that is a strong
risk factor for stroke. Additionally, tea has been shown to enhance
endothelial function, which, when reduced, impairs cerebral blood flow.
Furthermore, a compound found in tea known as theanine readily crosses
into the brain, where it may provide a neuroprotective effect.
"The
observational, epidemiological research in humans is strongly
supportive of the hypothesis that tea consumption, at the level of
greater than or equal to 3 cups per day, either as green or black tea,
reduces the risk of occurrence of stroke, stroke volume, and mortality
from stroke," the authors conclude.
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