A glass of wine with dinner has long been touted as heart healthy, but the scientific evidence for this claim doesn't pass muster, according to a new analysis of past research.
Researchers reviewed 87 studies that found a link between moderate drinking and longevity, and they found major problems with way the studies were designed. Their analysis calls into question the idea that alcohol may be linked with a longer life.
In fact, taken together, the data from all of these studies revealed that the people who end up the healthiest are those who barely drink, the researchers said.
"From a scientific standpoint, the relationship between alcohol consumption and health is obviously very important, and is a very controversial area," Dr. Tim Naimi, a physician and researcher at Boston Medical Center and co-author of the new review, told Live Science.
"We know that drinking too much is clearly bad for you — it kills about 100,000 people each year in the United States," Naimi said. But the other side of the question, that is, whether there are benefits of drinking a little alcohol, has been harder to answer, he added. [7 Ways Alcohol Affects Your Health]
"For the past 20 years many people have believed that 'moderate drinking' may be good for your heart," Naimi said, "but research doesn't actually back this up."
In the new analysis, published today (March 22) in the Journal of Studies on Alcohol and Drugs, the researchers combined information from previous studies that included a total of almost 4 million participants. Some of the studies spanned decades. Over the course of these studies, about 370,000 of the study participants died.
One major problem in most these studies, the researchers found, was that the researchers on these past studies compared moderate drinkers (people who have up to two drinks per day) to people who don't drink, or abstainers, without sufficiently accounting for the differences between them.
For example, many abstainers stay away from alcohol because of existing health issues, or because they had problems with excessive drinking in the past. Therefore, if moderate drinkers appear to have a health advantage, it could be because they are generally healthier than abstainers, and not because of they drink alcohol. (Only 13 of the 87 studies defined abstainers as people who had never drunk in their lifetime.)
When the researchers accounted for these differences, moderate drinkers lost their apparent tendency to live healthier, longer lives. "Compared with nondrinkers, so-called moderate drinkers had no survival advantage," Naimi said.
It turned out that among the drinkers, the group that actually did the best was the group the researchers called occasional drinkers. "These people drank at most one drink every 10 days," which is too little alcohol to provide any health benefits, he said. This finding highlights the idea that it is the other characteristics of these occasional and moderate drinkers that lead to their longer lives. [11 Interesting Facts About Hangovers]
For example, one such characteristic is that occasional and moderate drinkers are more likely than abstainers to belong to higher socioeconomic classes — a factor that was ignored in most studies. "People who drink moderately are actually the most socially advantaged people, and therefore more likely to lead healthier lives," Naimi said.
In other words, moderate drinking coincides with — rather than causes — a healthier outcome.
"One of the biggest limitations in this area of research is that there have been no randomized, gold standard type of studies, the kind that we would use to evaluate a new pharmaceutical product, for example," he said.
In addition, past studies have linked moderate drinking to a variety of health benefits including implausible ones, such as a lower risk of deafness, and contradictory outcomes, such as lower risk of liver cirrhosis, said co-author Tim Stockwell, director of the University of Victoria's Centre for Addictions Research in British Columbia, Canada.
"Either alcohol is a panacea, or moderate drinking is really a marker of something else," Stockwell said in a statement.
The limitations in the past studies could result from observational studies' tendency to take their data from large cohort studies, primarily designed to investigate cancer or heart disease. "They weren't really designed to study alcohol, so a lot of them include very limited questions about people's drinking, often collecting information about somebody's drinking at one point in time," Naimi said. "That's why they should be taken with a big grain of salt."
The new findings do not mean people should not enjoy a glass of wine, but rather that they shouldn't drink alcohol in the hope of health benefits, he said.
He recommended that people who decide to drink follow the U.S. dietary guidelines for alcohol consumption. The guidelines suggest that men drink no more than two drinks per day, and that women drink no more than one drink per day.