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Drinking likely doesn’t help protect the heart. Getty Images

Blood pressure and the risk of stroke increase steadily with increasing alcohol intake, even for moderate consumption, according to a large genetic study in The Lancet.

This runs counter to previous research suggesting that one or two drinks a day is “heart healthy.”

Previous studies have suggested that consuming small amounts of alcohol may lower the risk of heart disease and stroke. However, others indicate that the only safe level of alcohol consumption is zero.

Experts say the new research points to the potential harms of drinking alcohol, at any level. But the study is not the final word on the subject.

Researchers from the University of Oxford in the United Kingdom, Peking University, and the Chinese Academy of Medical Sciences, followed more than 500,000 people for about 10 years. They monitored participants for cardiovascular incidents such as stroke or heart attack.

The results show that men who consumed four drinks a day had on average a 38 percent higher risk of stroke.

Stroke risk increased steadily from low levels of alcohol intake to four drinks per day, the range of consumption studied by the researchers.

Blood pressure also increased with alcohol consumption.

The Dietary Guidelines for Americans defines one standard drink of alcohol as:

  • a bottle of regular beer
  • a small glass of wine
  • a single measure of distilled spirits

Very few women in the study drank alcohol, so the researchers could not determine what impact alcohol had on their risk of stroke.

As for the impact of alcohol on the risk of heart attack, the researchers said the results were less certain. This may be due to fewer people in the study having heart attacks, which could limit their ability to analyze the data.

The study was conducted primarily in China. In East Asian populations, many people have one or more genetic variants that leads them to experience an unpleasant reaction to alcohol. As a result, they often drink less.

Researchers used these variants, also known as alleles, to estimate people’s alcohol intake. People inherit these variants randomly at birth.

Benjamin Voight, PhD, a statistical and population geneticist at the University of Pennsylvania Perelman School of Medicine, said this provides “a natural version of a randomized controlled trial, where alleles are akin to an ‘intervention’ that changes a person’s alcohol use over their lifetime.”

He said this approach overcomes some of the problems of non-genetic large-scale population studies, also known as epidemiological studies.

But even the genetic analysis used in the study has its own limitations.

Dr. Gregory Marcus, director of clinical research for the division of cardiology at the University of California, San Francisco, pointed out that the majority of alcohol consumed in the study was hard liquor, or spirits.

Other caveats include the fact that the study was conducted only on people in China, so the results may not apply to people from other parts of the world.

Other types of alcohol — such as wine, with its protective phytochemicals — may affect stroke risk differently. The researchers could not tell based on their data.

Marcus also pointed out that genetic variants don’t pass from parent to child in complete isolation. They may “travel with” nearby variants that could affect stroke risk on their own.

The researchers write that their results suggest that there is no protective effect of moderate alcohol consumption — so any level of drinking carries some health risks.

“It’s more compelling data that the benefits of alcohol on cardiovascular disease may be less than was previously appreciated,” said Marcus.

Based on earlier research, he said the link between alcohol and stroke makes sense.

“In many ways, this is what I would expect,” said Marcus, “given the growing evidence that alcohol contributes to atrial fibrillation,” which is one of the common causes of stroke.

As for the link between alcohol and heart disease, Voight pointed to a previous study in The BMJ that used a similar analysis on different genetic variants in a European population.

In that study, some people had a variant related to drinking no or less alcohol. These people had a lower risk of coronary heart disease, compared to those without the variant.

This suggests that light to moderate drinking can be beneficial for heart health.

However, Marcus said without a true randomized trial, we won’t know for certain the health effects of alcohol.

This is the same kind of study used to see if pharmaceutical drugs are helpful or harmful — and yes, alcohol is a drug.

Until we have a well-designed randomized trial, he said we should be careful to avoid promoting moderate alcohol as definitely healthy.

“The harms of alcohol would seem to be more evident than the benefits,” said Marcus. “But the reality is that we still don’t know.”