Green, Black Tea Can Reduce Stroke Risk

I would think there has to be an upper limit on how much tea is helpful, considering the effects of caffeine.

http://www.sciencedaily.com/releases/2009/02/090223091806.htm

ScienceDaily (Mar. 4, 2009) — Drinking at least three cups of green or black tea a day can significantly reduce the risk of stroke, a new UCLA study has found. And the more you drink, the better your odds of staving off a stroke.

The UCLA researchers conducted an evidence-based review of all human observational studies on stroke and tea consumption found in the PubMed and Web of Science archives. They found nine studies describing 4,378 strokes among nearly 195,000 individuals, according to lead author Lenore Arab, a professor of medicine in the division of general internal medicine and health services research at the David Geffen School of Medicine at UCLA.

"What we saw was that there was a consistency of effect of appreciable magnitude," said Arab, who is also a professor of biological chemistry. "By drinking three cups of tea a day, the risk of a stroke was reduced by 21 percent. It didn't matter if it was green or black tea."
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Though no one is certain which compounds in tea are responsible for this effect, researchers have speculated that the antioxidant epigallocatechin gallate (EGCG) or the amino acid theanine may be what helps. Antioxidants are believed to help prevent coronary artery disease.

"And we do know that theanine is nearly 100-percent absorbed," Arab said. "It gets across the blood-brain barrier and it looks a lot like a molecule that's very similar to glutamate, and glutamate release is associated with stroke.

"It could be that theanine and glutamate compete for the glutamate receptor in the brain," she added.