Its conclusion: There is no level of drinking that does not confer heart disease risk. The risk is small if people have an average of seven drinks a week when compared with none. But it increases quickly as the level of alcohol consumption rises.
"Dose matters a lot," said Dr. Krishna G. Aragam, a preventive cardiologist at Massachusetts General Hospital and an author of the study. "Just realise that, as you go up beyond modest ranges, the risk goes up quite a bit."
The study, which may help resolve medical disputes over the effects of alcohol on the heart, involved sophisticated analyses of the genes and medical data of nearly 400,000 people who participate in the UK Biobank, a British repository that investigators use to study genes and their relation to health. The average age of subjects selected for the alcohol study was 57, and they reported consuming an average of 9.2 drinks a week.
Some researchers have reported that drinking modestly protects the heart because moderate drinkers as a group have less heart disease than those who drink heavily or those who abstain. Aragam and his colleagues also saw that effect. But the reason, they report, is not that alcohol protects the heart. It is that light to moderate drinkers — those who consume up to 14 drinks a week — tend to have other characteristics that decrease their risk, like smoking less, exercising more and weighing less than those who drink more heavily and those who do not drink.
It's not known why moderate drinkers tend to be more healthy than nondrinkers, Aragam said. But the Biobank study did not ask why people drank or abstained. Instead, it attempted to tease apart the effects of alcohol on the heart from the effects of other habits, behaviours and characteristics. To do that, the researchers used a method called Mendelian randomisation.
Researchers have found genetic variants that predispose a person to heavier or lighter drinking. Because the variants are distributed randomly in a population, they can serve in a study as the equivalent of randomly assigning people to abstain or to drink at varying levels. Researchers can ask if those with variants that are linked to greater alcohol consumption have more heart disease and high blood pressure than those with variants linked to lower consumption.
The investigators' statistical analysis showed an exponential curve of risk with the gene variants that suggest they drink more. The risks of heart disease and high blood pressure started slowly as the number of drinks increased, but they quickly gained steam, soaring as people got into the abusive drinking range of 21 or more drinks a week.
The actual risks to an individual depend on whether the person has other conditions, like diabetes or obesity. But, Aragam said, extrapolating from the results of the study, a typical middle-aged person in the study who did not drink had an estimated 9% chance of having coronary heart disease. A person who had one drink a day had an estimated 10.5% chance, which is small. After that, though, the risk increases quickly.
Many earlier studies of alcohol consumption and heart health were observational, meaning the subjects were followed over time to see if the amount of drinking was linked to heart health.
Such studies are only able to find correlation but not causation, researchers say. But the Biobank study's use of Mendelian randomisation is more suggestive of causality, and so its results might carry more weight.
"We have to start thinking about those moderate ranges and inform patients accordingly," Aragam said. "If you are choosing to drink, you should know that beyond a certain level, the risk ramps up quite a bit. And if you choose to drink less, you will get the bulk of your benefit if you go to the seven drinks a week range."
Dr. Amit V. Khera, an author of the study and a cardiologist at Verve Therapeutics, said that, of course, the gold standard to assess the heart effects of drinking would be a large randomised clinical trial. Such a study, which would have randomised high-risk people to one drink a day or abstinence, was planned in 2017 by the National Institutes of Health. But it was terminated because the researchers had inappropriate contact with the alcohol industry when they were planning the study.
Mendelian randomisation techniques, Khera said, "are particularly helpful when a gold standard hasn't been, or can't be, done."
Despite the difficulties in doing a randomised trial of drinking, one recent study in Australia offered clues. It involved 140 people with atrial fibrillation, a form of heart disease. At the start of the study, participants reported drinking an average of 17 drinks a week. A randomly selected group of 70 were asked to abstain and managed to reduce their consumption to an average of two drinks a week. Over the six-month study period, those in the control group had atrial fibrillation 1.2 per cent of the time compared with 0.5% for those randomised to abstain.
Hazen, the cardiologist in Cleveland, said the new Biobank study made him wonder about the effects of increased drinking during the pandemic. Researchers have noted that people have been drinking more since the pandemic began, and a recent report found that the number of alcohol-related deaths shot up 25 per cent in 2020.
Blood pressure also increased in the pandemic. Hazen and his colleagues, examining national data, found it rose on average by nearly 3 millimetres of mercury.
"We had no idea how it was happening," Hazen said.
Changes in participants' body weight did not account for the rise in blood pressure during the pandemic. The increase, which occurred in all 50 states and in Washington, DC, was a puzzle.
Now, he has a new thought.
"Oh, my gosh. Maybe increased drinking is accounting for the increase in blood pressure," Hazen said.
This article originally appeared in The New York Times.
Written by: Gina Kolata
Photographs by: Brett Carlsen
© 2022 THE NEW YORK TIMES
