Consideration of confounding in epidemiologic studies assessing alcohol consumption on the risk of breast cancer: A brief report

Background: Individual observational studies have suggested null, weak, linear, and J-shaped associations between alcohol consumption and breast cancer risk. However, observational studies are susceptible to confounders, which can obscure the true impact of an exposure on an outcome. Given the uncertainty regarding the association between alcohol consumption and breast cancer, and the challenges of identifying, measuring, and accounting for all potential confounders, we assessed whether and how authors of observational studies evaluating the impact of alcohol consumption on the risk of breast cancer considered bias when interpreting their main study findings. Methods: We identified all observational studies included in a recent alcohol-breast cancer meta-analysis. The Abstract and/or Discussion sections were reviewed to determine whether authors considered confounding. Results: Among 101 eligible studies, 73 (72.3%) mentioned confounding explicitly in the Abstract and Discussion sections. There were 33 (32.7%) studies that included statements regarding specific confounders that were not adjusted for in the analyses and 60 (59.4%) studies without any statements about the impact of residual confounding on their main findings. Although none of the studies outlined that their main findings were “likely” to be affected by residual confounding, 25 (24.8%) mentioned a “possible” impact and 16 (15.8%) claimed an “unlikely” impact. Only one (1.0%) article explicitly stated that caution was needed when interpreting their findings due to confounding. Conclusion: These results highlight the need for more adequate consideration of the potential impact of residual confounding in observational studies evaluating the impact of alcohol consumption on the risk of breast cancer.