the basic idea of the Mendelian randomization is to use genetic variables as instrumental variables, i.e., genes associated with an exposure (in this study, alcohol consumption or alcohol metabolism) but not directly related to outcome (in this study, HDL-cholesterol and other lipid parameters).  Since the genetic pattern is determined before birth, it should not (at least, in theory) be confounded by later lifestyle exposures or outcome variables.  Thus, it allows the investigators to make causal inference.

Mendelian randomization provides an approach to addressing questions of causality without many of the typical biases that impact the validity of traditional epidemiologic approaches. While Mendelian randomization studies can provide important suggestive evidence for causal relations between risk factor (consumption of alcoholic beverages in this case) and disease outcome (blood lipid levels), they are not true experiments and are dependent on several assumptions. Evidence from randomized controlled trials, when possible, should continue to guide clinical decisions.