How Does Booze Extend Your Lifespan?

Plus: Which kind of alcoholic drinks are best for your health?

People who drink heavily live longer than those who completely abstain from alcohol, according to a new study conducted by a psychologist at the University of Texas. How, exactly, does booze extend your lifespan?

It seems to decrease your risk of heart disease and diabetes, although no one knows exactly how that happens. Researchers are nearly certain that regular consumption of alcohol increases levels of HDL, the so-called “good cholesterol,” although physicians disagree on whether this can account for the decrease in heart disease among drinkers. Generally speaking, those who consume two beverages per day increase their HDL levels by between 5 percent and 10 percent, which some believe corresponds to a 10 percent reduction in risk for heart disease. Alcohol might also serve to reduce clotting and improve your heart’s pumping efficiency, but these results aren’t as well-established. A few studies have shown that drinking improves insulin sensitivity, which lowers your risk for diabetes, itself a risk factor for heart disease. For all that, a lack of ironclad data has left the door open to a handful of nonbelievers, who think confounding variables and shoddy methodology undermine all of the studies. They argue that the supposed health effects of alcohol might be better explained by the fact that people who drink in moderation have a healthier lifestyle all around.

Doctors have long suspected that imbibing has heath benefits. During the early years of Prohibition, a coalition of doctors went to the Supreme Court to fight for their right to prescribe alcohol for such disorders as upset stomach, chronic wasting disease, prolonged lactation, and tuberculosis. In 1926, just as the Supreme Court was rejecting the physicians’ plea, a Johns Hopkins researcher named Raymond Pearl published a book showing that people who drink a little bit of alcohol live longer than those who drink too much or not at all. Over the past eight decades, doctors have produced a mountain of paper trying to account for Pearl’s results, which have been repeated many times over.

Data on the benefits of drinking come in two flavors. Observational studies split participants into groups based on how much they claim to imbibe, then compare them. These experiments are relatively cheap and make for tolerable cocktail-party chatter. But doctors don’t like to rely on them, because it’s difficult to separate the effects of the alcohol from confounding factors. For example, drinkers are richer on average than teetotalers, and therefore have better access to health care. They also exercise more. On the other hand, those who drink are more likely to smoke, which increases their risk for all sorts of nasty diseases. Researchers try to control for these factors, but they cannot eliminate their influence completely.

Intervention studies take smaller groups of similar people and change the drinking habits of half of the participants. The problem is that such studies are expensive, and most people don’t like being told what to drink. As result, data can only be compiled over the span of a few weeks in most cases, so it’s hard to draw conclusions about long-term behavior.

Based on a comparison of these two types of studies, the evidence for an increase in HDL has the strongest credentials. (Drinking two servings of alcohol per day is better for HDL levels than exercising or quitting smoking.) But several studies have failed to show that increasing HDL actually wards off heart attacks, so doctors aren’t sure this can explain the relationship between alcohol consumption and longevity.

Bonus Explainer: If I’m going to drink for my health, which is the most potent potable?

It probably doesn’t matter. Early studies suggested that red wine was the best choice, but most people now attribute those findings to confounding variables. A Danish statistician, for example, reviewed supermarket receipts and found that people who buy wine are more likely to buy olives, fruits, and vegetables, while beer drinkers buy more sugar, butter, chips, prepared foods, and soft drinks. Some researchers argue that alcoholic beverages offer antioxidant benefits, though it’s not clear whether those differ from one drink to another, or, indeed, whether they exist at all. And don’t even think about drinking red wine for the anti-aging chemical resveratrol. No one really understands what it does, and studies on rodents suggest you’d need to consume at least 100 bottles a day for any effect.

Got a question about today’s news? Ask the Explainer.

Like  Slate  and the Explainer  on Facebook. Follow us on Twitter.