Last week, two patients asked Stanley L. Hazen, a cardiologist at the Cleveland Clinic, how much daily alcohol it would be good for your heart health. He gave both well-accepted medical advice: an average of one dose a day helps the heart. “I didn’t even think twice,” he said.
But then he read an article published in JAMA Network Open whose findings overturned her thinking about what to say to patients. The article, he said, “changed my life completely.”
Their conclusion: there is no level of alcohol consumption that does not confer risk of heart disease. The risk is small when people consume an average of seven drinks a week compared to none. But it increases rapidly as the level of alcohol consumption increases.
“Quantity matters a lot,” said Krishna G. Aragam, a preventive cardiologist at Massachusetts General Hospital and one of the study’s authors. “The important thing is to know that as you go beyond the more moderate ranges, the risk goes up a lot.”
The study, which could help resolve medical disputes over the effects of alcohol on the heart, involved sophisticated analyzes of the genes and medical data of nearly 400,000 people registered at the UK Biobank, the British repository that researchers use to study genes and their implications for the health. The average age of subjects selected for the alcohol study was 57 years, and they reported consuming an average of 9.2 drinks per week.
Some researchers have reported that drinking modestly protects the heart because moderate drinkers, taken together, have less heart disease than heavy drinkers or non-drinkers. Aragam and his colleagues also identified this effect. But the reason, they report, is not that alcohol protects the heart. It’s just that light to moderate drinkers — those who consume up to 14 drinks a week — tend to have other characteristics that lower their risk, such as smoking less, exercising more, and weighing less than those who drink more and those who don’t.
It’s not known why moderate drinkers tend to be healthier than people who don’t drink, Aragam said. But the Biobank study didn’t ask why people drank or didn’t, it just tried to make a distinction between the effects of alcohol on the heart and the effects of other habits, behaviors and traits. To do this, the researchers used a method called Mendelian randomization.
Researchers have discovered genetic variants that predispose a person to drink more or less. As the variants are randomly distributed in a given population, they can function within a study as something equivalent to randomly assigning some people to abstain or drink at varying levels. Researchers might ask whether people with variants linked to higher alcohol consumption have more heart disease and high blood pressure than people with variants linked to lower consumption.
The researchers’ statistical analysis showed an exponential curve of risk with the genetic variants that suggest higher levels of consumption. The risks of heart disease and high blood pressure started to slowly rise as the number of drinks increased, but they quickly gained momentum, exploding as people entered the binge drinking range of 21 or more drinks a week.
The most serious risks depend on whether the person has other conditions, such as diabetes or obesity. But, Aragam said, extrapolating the study results, a typical middle-aged person who didn’t drink had an estimated 9% chance of having coronary heart disease. A person taking one dose a day had an estimated chance of 10.5%, which is low. From there, however, the risk increases rapidly.
Many previous studies of alcohol consumption and heart health were observational, meaning that subjects were followed over time to see if the amount of drinking was linked to heart health.
These studies can only find correlation, not causation, the researchers say. But the use of Mendelian randomization in the Biobank study is more suggestive of causality, and therefore its results may carry more weight.
“We have to start thinking about these moderate intervals and informing patients in the right way,” Aragam said. “If you choose to drink, you need to know that beyond a certain level, the risk goes up a lot. And if you choose to drink less, you will get most of the benefit if you stay in the seven-drink-a-week range.”
Amit V. Khera, one of the study’s authors and a cardiologist at Verve Therapeutics, said the gold standard for assessing the drink’s cardiac effects would, of course, be a large randomized clinical trial. A study like this was even planned in 2017 by the National Institutes of Health. But it was closed because the researchers had inadequate contact with the alcohol industry while they were planning the study.
Mendelian randomization techniques, Khera said, “are particularly useful when a gold standard has not or cannot be done.”
Despite the difficulties in doing a randomized trial of drinking, a recent study in Australia offered some clues. The Australian study 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 per week.
A group of 70 randomly selected people were asked to abstain and were able to reduce their consumption to an average of two drinks per week. During the six-month period of the study, people in the control group had atrial fibrillation 1.2% of the time compared to 0.5% for people randomized to drink less.
Hazen, the Cleveland cardiologist, said the new Biobank study made him wonder about the effects of increased alcohol consumption during the pandemic. Researchers have noted that people have been drinking more since the start of the pandemic, and a recent report found that the number of alcohol-related deaths increased by 25% in 2020.
Blood pressure has also increased in the pandemic. Examining national data, Hazen and his colleagues found it increased on average by nearly 3 millimeters of mercury. “We had no idea how this was happening,” Hazen said.
Changes in participants’ body weight were not responsible for the rise in blood pressure during the pandemic. The increase, which took place in all 50 states and in Washington, DC, was an enigma.
Now he has a new reasoning. “Oh my God. Perhaps increased alcohol consumption is responsible for the rise in blood pressure,” Hazen said./ TRANSLATION BY RENATO PRELORENTZOU