PHILADELPHIA--For years, researchers have struggled to learn exactly why moderate drinkers are less prone to heart disease than those who abstain or hardly drink at all. Is it the alcohol itself, or something else in their drinks? Now, a genetic study may tip the scales in favor of alcohol. But the finding, announced here 6 October at the annual meeting of the American Society of Human Genetics, also shows that the protective effects of a drink depend on your genes.
Since the early 1980s, studies have shown that moderate drinkers live longer and are less likely to suffer a heart attack than teetotalers. Several compounds have been touted as responsible for this benefit. Most recently, a study pointed to resveratrol, an antioxidant found in red wine (ScienceNOW, 10 July). But Lisa Hines and her colleagues at the Harvard School of Public Health in Boston believe that ethanol--the scientific word for the alcohol in your drink--deserves the credit.
To back up her hunch, Hines looked at ADH3, a gene responsible for the breakdown of alcohol by oxidation. Her investigation was based on a previous observation: The rate at which the liver breaks down ethanol depends on which copies of the ADH3 genes people carry. So if it's ethanol that lowers the risk of heart disease, Hines speculated, then slow oxidizers should on average have the healthiest hearts, because the ethanol would hang around longer in their bodies.
And that's what she found, after analyzing DNA samples from 396 men with heart disease and 770 controls. Among subjects with slow ethanol metabolism, moderate drinkers had a 86% lower risk of heart disease than nondrinkers. Moderate drinkers who metabolize ethanol quickly didn't fare so well. Their risk of cardiovascular trouble was only 38% less than those who abstained from alcohol. Drinkers with the slow genes--who make up about 16% of the Caucasian population--also tended to have elevated blood levels of high density lipoproteins, which reduce the risk of heart disease.
"It's a good start, a good study, but it's not the whole answer," says Sam Zakhari, a pharmacologist at the National Institute on Alcohol Abuse and Alcoholism. Other factors, such as weight and gender, also affect how long alcohol stays in the bloodstream, Zakhari says, and they too will play a role if ethanol does indeed protect from heart disease. Hines, for her part, cautions that her study shows benefits only for light to moderate alcohol consumption: "We're not advocating that everyone go out and drink."
Hines's abstract from the American Society of Human Genetics meeting