Anyone who’s still drinking alcohol "for their health" should listen up.
Past research has shown that the chemicals in red wine may help fight aging and lower risk for cardiovascular disease and cancer. And indeed, research shows that moderate alcohol drinkers have longer lives than people who abstain. There's just one problem with this conclusion: These studies often make the crucial mistake of including participants who abstain from alcohol for reasons that should exclude them.
Now, a new review of 87 previous studies reveals that controlling for the right demographic factors contradicts findings that alcohol consumption is linked to a longer life. These studies, which included data from about four million people and 370,000 deaths, all showed that moderate, “low-volume" drinkers (one to two drinks a day) were less likely to die than people who abstained from alcohol. But that doesn't mean moderate drinking led to longer life, and this new review suggests that it doesn't.
Here's what 'abstaining' really means
Many people who fully abstain from alcohol do so because of medical conditions. They may quit drinking due to a medical condition or health consideration. Either way, these factors bias the “abstainer” group toward worse health than the general population that produces the "moderate" group.
"Giving up drinking is a sign of ill health, not a cause of it," said Tim Stockwell, a psychology professor at the University of Victoria in Canada and the director of the Center for Addictions Research of BC. "So if those people are put in the abstainer comparison group, they make that group look unhealthy and make the moderate drinkers look healthier by comparison."
A more precise way to compare the effects of alcohol on health would be to compare moderate drinkers to those who have abstained their whole lives, rather than include former drinkers, argued Stockwell.
Other factors that affect the quality of a study include controls for smoking status, age and ethnicity -- something that low-quality studies did not do.
What happens when we fix the 'abstainer' bias
When Stockwell adjusted the abstainers group to exclude former drinkers, or excluded studies that didn’t properly define abstainers as lifelong teetotalers, the results changed dramatically. Moderate drinkers no longer had a lower-than-usual risk of all-cause mortality. That honor now went to the “occasional” drinkers, who drink between one drink a year to three drinks per month.
Because this amount of alcohol is so low, it’s unlikely to have any influence on health, positive or otherwise, Stockwell said. He doubts that these occasional drinks have anything to do with their long lives.
Stockwell hopes that his analysis can help people have a more realistic perspective about the effect their drinking habit has on their life. If people are drinking for the supposed health benefits, he said, they should also be aware that alcohol is a neurotoxic, carcinogenic substance that also happens to be addictive. Even if scientists did find a medicinal purpose for alcohol, Stockwell explained, the drink also comes with other risks that may cancel out its purported benefits.
"We can’t rule out that alcohol isn’t still preventing heart disease, but it’s balanced by the extent to which it’s causing cancers and other problems,” Stockwell said. "There’s no safe level of drinking."
What this means for people who love a stiff drink
In a commentary that accompanied Stockwell’s meta-analysis, Thomas Greenfield, scientific director of the Alcohol Research Group in Emeryville, California, praised the findings. He said it could help fight back against "renewed calls from certain medical commentators to prescribe moderate drinking."
Jennie Connor, a chair in preventive and social medicine at the University of Otago in New Zealand, added that media reports on the health benefits of alcohol don’t do enough to point out the unequal effect alcohol has on different segments of the population, like people who are more prone to alcohol use disorders.
The U.S. dietary guidelines state that moderate drinking, which means one drink per day for women and up to two drinks per day for men, can be part of a healthy lifestyle. But they also state that there are no health benefits so compelling that they justify drinking for wellness alone, which means adults who don’t imbibe shouldn't start the habit now.
Stockwell agrees with these guidelines, but also points out that he hopes Americans don’t interpret that it’s "healthy" to drink the recommended levels of alcohol -- rather, that it’s merely "low-risk."
"People should drink for pleasure and enjoyment, but with care," Stockwell concluded. "The more you drink, the higher risk you’re at for serious diseases."
Stockwell's study was funded by the National Institutes of Health and published in the Journal of Studies on Alcohol and Drugs. He declared conflicts of interest that ranged from a 30-year-old grant from Merck to study an alcohol dependence drug to a current contract advising the Swedish government on how alcohol affects the country's health and safety.
UPDATE: This story was updated to include the most recent graphic from the research group.