The purported health benefits of low-volume alcohol consumption may be largely due to study biases, according to a new study.
Researchers, led by Tim Stockwell, PhD, of the University of Victoria, analyzed 107 cohort studies with a total of 4,838,825 participants and 425,564 recorded deaths to identify study characteristics that may have biased estimates of all-cause mortality risk associated with low-volume drinking.
Methods
The researchers coded studies based on characteristics predicted to bias results toward low-volume drinkers appearing to live longer than abstainers. These included abstainer bias (contamination of nondrinking reference groups with former and/or occasional drinkers), median cohort age, baseline illness exclusion, alcohol measurement (spanning ≥ 30 days vs < 30 days), smoking and socioeconomic status (SES).
Low-volume drinking was defined as consuming between 1.3 g and 24 g of ethanol per day (approximately 1 drink per week to 2 drinks per day). The study primarily used three quality criteria: younger cohort age, absence of abstainer bias, and higher quality alcohol measurement, according to results published in the Journal of Studies on Alcohol and Drugs.
Results
In exploratory bivariate analyses, studies with the following characteristics showed significantly lower all-cause mortality risk for low-volume drinkers: older cohorts, abstainer bias, poor quality alcohol use measures, inclusion of participants with pre-existing health conditions, and control for smoking status and SES.
Meta-analyses of 6 higher-quality studies (median cohort age ≤ 55 years, no abstainer bias) found no significant reduction in mortality risk for low-volume drinkers (relative risk [RR], 0.98; 95% CI, 0.87-1.11). In contrast, 18 lower-quality studies (median cohort age >55 years, abstainer bias present) showed a significantly lower mortality risk (RR, 0.82; 95% CI, 0.76-0.89).
In 6 studies stratified by smoking status, low-volume drinkers had a nonsignificant RR of 1.16 (95% CI, 0.91-1.41) among nonsmokers and 0.93 (95% CI, 0.71-1.16) among smokers. Notably, none of the 107 studies presented results stratified by SES.
Conclusions
The apparent health benefits for low-volume drinkers could be consistently created in studies prone to biasing the abstainer reference group toward ill health. Researchers suggested few published studies meeting quality criteria to avoid this bias showed reduced mortality risk for low-volume drinkers. The identified biases pervaded alcohol epidemiology research and has led to confusion regarding alcohol-related health risks.
There is a need for future research to investigate whether smoking status mediates, moderates, or confounds alcohol-mortality risk relationships, as adjustment for smoking may have biased results. The authors also noted that these findings have significant implications for global disease burden estimates and national guidelines on low-risk alcohol use.
Limitations of the study included the small number of high-quality studies available and potential issues with alcohol consumption measurement in many of the analyzed studies.
Conflict of interest disclosures are available in the study.