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Drinking excessive amounts of alcoholic beverages damages many organs, particularly the liver, brain, and heart. Paradoxically, however, beginning about 50 years ago, studies began to suggest that moderate drinking might actually be good for the heart. Moderate drinking is defined as one to two drinks per day for a man, and one drink per day for a woman. A "drink" is defined as a shot (1.5 ounces) of spirits, a 5-ounce glass of wine, or a 12-ounce bottle of beer.
The evidence for a heart benefit from moderate drinking comes from observational research involving hundreds of thousands of people whose drinking patterns and health have been closely followed for decades. People in these investigations have been divided into roughly three groups: nondrinkers, moderate drinkers, and more-than-moderate drinkers. Over time, moderate drinkers have had lower rates of coronary artery disease (including fewer heart attacks) compared to both of the other two groups.
"That makes sense, since other studies have found that moderate drinking causes 'good' cholesterol to rise and blood to clot a bit less easily — both of which could explain a lower rate of heart attacks," says Dr. Anthony Komaroff, an internal medicine specialist and Health Letter editor in chief.
Based on these results, the current Dietary Guidelines for Americans recommend drinking only in moderation, if at all. Other authoritative organizations — such as the CDC and the American Heart Association — have echoed this advice. However, none of these guidelines recommend moderate drinking as a way of protecting against heart disease, because observational studies cannot prove the value of a drug or a practice, such as moderate drinking.
If an observational study finds that people who have just one drink a day are less likely to develop heart disease than people who do not drink, that does not necessarily mean that the moderate drinking pattern is the reason for the lower rate of heart disease. Maybe moderate drinkers are different in some other way (which the studies did not measure) that protects them from developing heart disease.
For example, suppose moderate drinkers also are more likely than nondrinkers to engage in other practices that are heart-healthy, but that are not yet known to be so, and therefore are not measured by the study. Maybe it's those other practices, not the moderate drinking, that explains the lower risk of developing heart disease.
Or suppose that the nondrinkers are born with a gene that gives them an unpleasant reaction when they drink alcohol — and that's why they don't drink. Suppose that same gene also raises their risk of getting heart disease. No such gene has been discovered, but it could exist. If that gene is the reason nondrinkers have more heart disease than people who take a drink a day, then people without that gene would get no heart benefits from taking a drink a day.
"Good observational studies do their best to take account of all the factors that might affect an outcome," Dr. Komaroff says, "Unfortunately, they can't be done perfectly, and they can't take account of risk factors that have not yet been discovered."
The way to prove the value of any kind of treatment, including nutritional practices like moderate drinking, is to conduct randomized controlled trials. In such trials, the treatment or practice is assigned at random to some people and not to others. That way, there are two groups of people who are very similar in all respects but one — in this case, whether or not they drink in moderation. The health of both groups would be carefully monitored over time.
An ideal randomized trial of moderate drinking would assign many thousands of people, at random, to either take one drink a day or to never drink — every day, for years — and to undergo regular checks to determine if they were actually doing what they were assigned to do. Such a study would provide strong evidence as to whether people who had one drink each day were less likely to develop heart disease than those who never drank. Some randomized trials of nutritional practices have been conducted, but it's not easy to find people willing to participate.
In considering whether moderate drinking improves heart health, we are left with large observational studies. Several recent investigations have not found clear evidence that people who take a drink a day are less likely to develop heart disease than people who don't drink. This new evidence doesn't negate past studies; it simply must be weighed against past studies.
As of now, the evidence leads us to these conclusions:
"We all wish science could provide definitive and permanent answers to important questions, but that is rarely the case," Dr. Komaroff says. "The best that we can do is give you our current assessment of how we weigh the sometimes-conflicting evidence. Stay tuned!"
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