Drinking alcohol is associated with an immediate higher risk of suffering a heart attack or stroke. The risk lessens and can become protective after 24 hours for moderate drinking but remains high for heavy drinking, according to research presented at the American Heart Association's Epidemiology and Prevention/Lifestyle 2016 Scientific Sessions.
The study, a systematic review and dose-response meta-analysis of previous research, will also be published simultaneously in the American Heart Association's journal Circulation.
"There appears to be a transiently higher risk of heart attack and strokes in the hours after drinking an alcoholic beverage but within a day after drinking, only heavy alcohol intake seems to pose a higher cardiovascular risk," said Elizabeth Mostofsky, Sc.D., study lead author, instructor at the Harvard T.H. Chan School of Public Health and post-doctoral fellow at Beth Israel Deaconess Medical Center in Boston, Massachusetts.
Previous research has described cardiovascular risks following moderate and heavy alcohol consumption, but the immediate risks have not been well documented.
"Ours is the first to synthesize all the available information to gain new knowledge on the acute risk of heart attacks and strokes in the hours after drinking and the risk in the following week for different amounts of alcohol consumed," Mostofsky said.
Researchers analyzed evidence on the risk of heart attacks and strokes in the hours and days after drinking alcohol from 23 studies that included nearly 30,000 participants.
Immediately following alcohol intake, there are both harmful and protective physical responses. Within one to three hours, a single dose of alcohol increases heart rate and disrupts the heart's normal pacing but by 24 hours, moderate alcohol intake improves blood flow, blood vessels' lining function and reduces clotting.
Moderate drinking - up to six drinks a week in this study - was associated with an immediately higher cardiovascular risk but within a day was considered protective and associated with a lower risk of a having heart attack or stroke from bleeds and within the week was associated with a lower risk of strokes from clots.
However, heavy alcohol use was associated with higher heart attack and stroke risks at all times studied: six to nine drinks in a day nearly doubled the risk and 19 to 30 drinks in a week elevated the risk by up to six times more.
Heavy drinking is typically described for men as consuming 15 or more drinks per week and more than 8 drinks per week for women. According to the 2015 Dietary Guidelines for Americans, moderate drinking is up to 1 drink per day for women and up to 2 drinks per day for men.
"Just after drinking, blood pressure rises and blood platelets become stickier, increasing the risk of heart attacks and strokes," Mostofsky said. "However, regularly drinking small amounts of alcohol in the long term appears to both increase levels of HDL cholesterol (high density lipoprotein cholesterol), the so-called good cholesterol, and reduce the tendency to form blood clots."
"If you drink alcohol, do so in moderation," she said.
Likewise, the American Heart Association recommends consuming alcohol in moderation if you already drink but cautions people to not start drinking and consult your doctor on your risks and benefits of consuming alcohol in moderation.
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