Why Do Only Some Cohort Studies Find Health Benefits From Low-Volume Alcohol Use? A Systematic Review and Meta-Analysis of Study Characteristics That May Bias Mortality Risk Estimates.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of observational cohort studies
PubMed 38289182 · doi:10.15288/jsad.23-00283
What was done
The authors conducted a systematic review and meta-analysis of 107 longitudinal cohort studies (724 estimates, 4,838,825 participants, 425,564 deaths) evaluating low-volume alcohol use (1 drink/week [>1.30 g ethanol/day] to 2 drinks/day [<25 g ethanol/day]) and all-cause mortality. Higher-quality studies were defined as having a mean cohort age of 55 years or younger, follow-up past age 55, and excluding former and occasional drinkers from abstainer reference groups. Mixed linear regression modeled relative risks (RRs) across study subgroups and exploratory adjustments for smoking and socioeconomic status.
What was found
Higher-quality studies controlling for reference group contamination and cohort age found no significant mortality reduction for low-volume drinkers compared to abstainers (RR = 0.98, 95% CI [0.87, 1.11]). Studies not meeting these quality criteria reported a statistically significant lower risk of mortality for low-volume drinkers (RR = 0.84, 95% CI [0.79, 0.89]). Studies adjusting for smoking and/or socioeconomic status reported lower risk estimates, but analyses restricted to nonsmoking cohorts showed an RR of 1.16 (95% CI [0.91, 1.41]) for low-volume drinkers.
Why it matters
Health benefits frequently attributed to moderate drinking appear to be artifacts of lifetime selection bias, specifically classifying unhealthy former drinkers as abstainers. When these biases are eliminated, low-volume alcohol consumption provides no detectable survival advantage.
Limits
The underlying evidence is limited to observational cohort designs with self-reported alcohol intake, which remains susceptible to measurement error and recall bias. The abstract does not provide cause-specific mortality breakdowns (e.g., cardiovascular disease versus cancer) or detailed assessments of heavy episodic drinking patterns.
Cited by
- supports Light and moderate alcohol drinkers have better dental hygiene, exercise routines, weight, diet quality, and income compared to abstainers.
- supports When studies adequately control for confounding factors like the healthy user effect and sick quitter bias, most or all of the protective effects of alcohol on disease risk are eliminated.