The J-shaped curve-conceptual and methodological challenges

Purpose The purpose of this paper is to review the conceptual and methodological challenges of a J-shaped association between alcohol consumption (AC), coronary heart disease (CHD) and all-cause mortality. In associated papers in this journal, Skovenborg et al., 2021 reviews the evidence for the J-shaped curve, and Ellison et al., 2021 examines the advantages and drawbacks of Mendelian randomization studies of the J-shaped curve. Design/methodology/approach A number of methodological problems are common in observational research in general, and some of the methodological problems suggested for the J-shaped alcohol-CHD-associations are discussed. The extent of the methodological problems in studies of the J-shaped curve is reviewed, and the possibility that the J-shaped curve is an artifact created by reverse causality and residual confounding is discussed. Further, the issue of interaction with drinking pattern and type of alcohol is discussed. Findings Imprecise categorization of alcohol intake information seems to have had little effect on the J-shaped alcohol-CHD-associations, nor has it affected the ability of these studies to show increasing mortality from a range of causes with increasing AC. The problem of "sick quitters" has been resolved by large studies using lifelong abstainers or infrequent drinkers as reference group. Many studies lack information on drinking patterns with regard to regular, moderate consumption versus binge drinking. Stratified analyses by important risk factors for CHD have not significantly changed the J-shaped association observed in most epidemiologic studies. Originality/value Potential biases and residual confounding probably do not overcome the J-shaped alcohol-CDH-association observed in most epidemiologic studies; however, the existence of a J-shaped curve is challenged by some degree of uncertainty. The actual review together with the associated papers by Skovenborg et al., 2021 and Ellison et al., 2021 offers a possibility to "update your priors" and achieve greater certainty when giving your patients information on the pros and cons of alcohol intake.