In a landmark systematic review of existing medical literature, researchers publishing in the Journal of Studies on Alcohol and Drugs found that previous research concluding that moderate alcohol consumption had health benefits was seriously flawed.
For decades, conventional wisdom, based on previous research, has held that moderate alcohol consumption—four to five drinks a week for adults—has some health benefits and may even be associated with longer life expectancy. But that view is increasingly being challenged, and scientists who reviewed 107 published studies on alcohol consumption and health now report that many of them contained a key methodological flaw that seriously called into question their conclusions.
These studies have focused on older adults in an attempt to demonstrate a link between alcohol and longevity, the researchers report, and many such studies have not distinguished between adults who now drink moderately but who previously drank little or not at all, and those who now drink moderately after a lifetime of potentially harmful drinking habits. This difference, the researchers say, is crucial: “Lower-quality” studies that did not ask self-described moderate drinkers about their past drinking habits appear to show that drinking is linked to longer life, while “higher-quality” studies that controlled for subjects’ drinking histories have shown no such correlation.
These higher-quality studies also had an average age cohort of 55 years or younger and follow-up of subjects beyond 55 years, adding to their methodological rigor. The 107 studies reviewed by the authors covered the experiences of 4,838,825 participants, including 425,564 recorded deaths.
“If you look at the weaker studies, that’s where you see health benefits,” lead researcher Tim Stockwell, a scientist at the Canadian Institute for Substance Use Research at the University of Victoria, said in a statement.
Widespread misconceptions that limited or moderate alcohol consumption is healthy could be harmful, researchers say.
“Studies with lifetime selection bias can create misleading positive associations with health,” the authors write. “These biases are pervasive in the field of alcohol epidemiology and can confound communications about health risks.”
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