But scientists were unsure if that was because the alcohol was beneficial or if the people who didn't drink had other health issues. "This should help inform personal choices and public health strategies", said Liming Li, a researcher at Peking University and study co-author. One drink was defined as either a small glass of wine, a bottle of beer or a single measure of spirits.
For the new study, the Chinese and British scientists took genetics into account.
In East Asian populations, there are common genetic variants that greatly reduce alcohol tolerability, because they cause an extremely unpleasant flushing reaction after drinking alcohol. For those with the variants, drinking alcohol can result in quickly turning red, a fast heart rate, nausea or headaches.
As the genetic factors that strongly affect drinking patterns are allocated randomly at conception and persist lifelong, this study is the genetic equivalent of a large randomised trial, and can therefore sort out cause-and-effect relationships reliably - a method called "Mendelian randomisation". Therefore, they can be used to study the causal effects of alcohol intake. Overall, it found that alcohol boosts stroke risk by about one-third for every four additional drinks a day.
"The claims that alcohol has some magical, protective fix. has no particularly serious scientific basis", said study co-senior author Richard Peto, University of Oxford, U.K., the AP reported.
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The subjects were followed for 10 years, and over 160,000 people had one of the two genetic variants that significantly reduced their alcohol consumption to almost zero per day. They recorded their medical history, including whether they smoked or exercised, and how much they drank.
The female participants in the study drank less than men, with just 2% drinking most weeks. In over 160,000 of these adults the researchers measured two genetic variants (rs671 and rs1229984) that substantially reduce alcohol intake. Among the men in that group, drinking ranged from none to up to four drinks a day. "The findings for heart attack were less clear-cut, so we plan to collect more evidence".
It is already known that heavy drinking is harmful to health and increases stroke risk - but some studies have suggested drinking small amounts can be good for the health, while others indicate there is no safe level of alcohol consumption. At least for stroke, the genetic evidence now refutes the claim that moderate drinking is protective.
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. There weren't enough heart attacks among the participants to be able to draw a conclusion about heart risks, the researchers said.
"Alcohol Focus Scotland believes the introduction of mandatory labelling of alcohol drinks, including number of units and health warnings, would help each of us to understand and manage our risk of alcohol health problems". "The alcohol industry is thriving and should be regulated in a similar way to the tobacco industry".