April 5 (UPI) -- For years, people have thought having a couple of drinks a day may lower their risk of stroke but it turns out the opposite may be true, a new study says.
The risk of having a stroke increases by 35 percent for every four extra drinks a person consumes, according to research published Thursday in The Lancet.
"Using genetics is a novel way to assess the health effects of alcohol, and to sort out whether moderate drinking really is protective, or whether it's slightly harmful. Our genetic analyses have helped us understand the cause-and-effect relationships," Iona Millwood, a researcher at the University of Oxford and study lead author, said in a news release.
People with genes increase risk for high alcohol intake are more likely to drink excessively, and be at higher risk for high blood pressure and stroke.
For the study, the researchers followed more than 500,000 people in China for 10 years. More than 160,000 of them had genetic variants that greatly reduced their alcohol intake from close to zero to about four drinks a day.
Men with the variant had a 50-fold difference in intake than those without it. This told the researchers that not only does alcohol increase the stroke risk but moderate drinking does nothing cut it down.
"There are no protective effects of moderate alcohol intake against stroke. Even moderate alcohol consumption increases the chances of having a stroke. The findings for heart attack were less clear-cut, so we plan to collect more evidence," said Zhengming Chen, a researcher at the University of Oxford and co-author.
After the 10-year follow-up, about 10,000 men had suffered strokes and 2,000 had heart attacks, which the researchers say suggests drinking has a greater effect on the heart.
In the U.S., about 140,000 people die each year from stroke, according to the Centers for the Disease Control and Prevention.
"Stroke is a major cause of death and disability. This large collaborative study has shown that stroke rates are increased by alcohol. This should help inform personal choices and public health strategies," said Liming Li, a researcher at Peking University and study co-author.