Coffee or Tea Consumption May Lower Stroke Risk
Drinking more of either beverage seems to bestow benefits, studies show
By Kathleen Doheny
FRIDAY, Feb. 20 (HealthDay News) -- Here's some good news for java junkies and tea lovers alike: Two new studies suggest that both beverages may lower your stroke risk.
As coffee drinking increases, the prevalence of stroke decreases, said Dr. David Liebeskind, author of the coffee study and an associate clinical professor of neurology at the University of California, Los Angeles.
He evaluated the association between coffee drinking and stroke by looking at data from the Third National Health and Nutrition Examination Survey, taken in 1988-94. He zeroed in on the 9,384 adults older than 40 who were coffee drinkers. Of those, 500 (5 percent) had been told by their doctor that they'd had a stroke. And 2,793 (29.8 percent) had self-reported stroke symptoms or a mini-stroke, also known as a transient ischemic attack.
When he looked at stroke prevalence and coffee drinking, Liebeskind found that the more coffee the adults drank, the less likely they were to have a stroke or a mini-stroke. Those who drank six or more cups a day, he found, had a stroke prevalence of 2.9 percent, whereas those who drank just one or two cups daily had a stroke prevalence of 5 percent.
The finding was presented Thursday at the International Stroke Conference in San Diego.
This latest coffee study comes on the heels of a study published in the February issue of Circulation that found long-term coffee consumption is linked with a lower stroke risk in women who don't smoke. To come to that conclusion, researchers followed more than 83,000 women who enrolled in the study in 1980 with no history of stroke, heart disease, diabetes or cancer.
They found stroke risk was 20 percent lower in those drinking four or more cups a day and 12 percent lower in those who had coffee five to seven times a week.
Tea drinkers may have reason to enjoy their brew, too, according to another study presented at the San Diego meeting.
Those who drink more than three cups a day had a 21 percent lower risk of stroke than those who sipped less than a cup daily, said study author Dr. Lenore Arab, a professor of medicine and biological chemistry at the University of California, Los Angeles.
She conducted a meta-analysis, pooling the results of nine published studies involving 4,378 strokes among more than 194,000 people, many from Asia. Black tea and green tea were studied, and it was typically caffeinated.
The result was that increased tea consumption decreased the risk. "We see it consistently in every study," Arab said. The research was funded by the Unilever Lipton Institute of Tea, a research and development arm of Lipton Tea.
Exactly how tea reduces stroke risk isn't clear, she said. Among the suggested ways it might work is by anti-inflammatory action. An amino acid found in black and green tea, theanine, may protect the brain.
The tea study is stronger than the coffee study, said Dr. Ralph Sacco, chairman of the department of neurology at the University of Miami Miller School of Medicine.
The coffee study, though interesting, "still needs confirmation," he said. The research was like a snapshot in time, asking people about coffee habits at a given point.
Better, he said, is to do a study in which participants are followed over time to determine if there is a link between coffee drinking and stroke.
He also wondered if coffee drinking might have decreased among those who were diagnosed with heart or other problems and were advised to reduce their coffee intake. "I don't feel this study is strong enough to recommend people drink coffee to reduce the risk of stroke," he said.
To learn more about reducing the risk of stroke, visit the American Stroke Association.
第１の研究は、米カリフォルニア大学ロサンゼルス校（UCLA）のDavid Liebeskind博士が、1988～94年に実施された第３回米国民健康栄養調査（NHANES）のデータを調べ、コーヒー消費量と脳卒中との関係を 評価したもの。40歳以上でコーヒーを飲む習慣のあった9,384人のうち、脳卒中の診断を受けたのは500人（５％）、自己申告による脳卒中の症状また は一過性脳虚血発作（TIA）の経験があったのは2,793人（29.8％）であった。分析の結果、１日に６杯以上コーヒーを飲む人の脳卒中罹患率は 2.9％であったのに対し、１日１～２杯しか飲まない人の罹患率は５％であることが示された。
この研究が発表される少し前に米医学誌「Circulation（循環器）」オンライン版に2月16日に掲載された研究では、1980年に被験者登録さ れた脳卒中、心疾患、糖尿病、癌（がん）の既往のない女性８万3,000人強を追跡した結果、１日に４杯以上コーヒーを飲む人は脳卒中リスクが20％低 く、週に５～７杯飲む人では12％低いことが報告されている。
第２の研究では、１日３杯を超える茶を飲む人は、１日１杯未満しか飲まない人に比べて脳卒中リスクが21％低いことが示された。UCLA教授の Lenore Arab博士は、19万4,000人強を対象とした９件の研究について、一般的にカフェインが含まれる紅茶および緑茶についてメタアナリシス（分析）を 行った（多くがアジアからのデータ）。4,378人が脳卒中を発症しており、どの研究でも一貫して茶の摂取量が多いほどリスクが低下することが判明。その 機序は明らかにされていないが、抗炎症作用や紅茶や緑茶に含まれるアミノ酸のテアニン（theanine）の作用によるものと考えられている。この研究は ユニリーバ/リプトン紅茶研究所の支援により実施された。
米マイアミ大学ミラー医学部のRalph Sacco博士は、コーヒーよりも茶に関する研究の方が信頼性は高いと指摘している。コーヒーの研究は、被験者のある一時期でのコーヒー摂取について尋ね たものであり、脳卒中との関連の有無を明らかにするには、長期的に被験者を追跡する研究が望ましいという。