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Critique 176: A New Report on Alcohol Consumption and Total Mortality Risk — 14 December 2015

Most observational studies have found that moderate drinkers, in comparison with nondrinkers, tend to have lower risk of all-cause (total) mortality; this is probably related primarily to a reduction in the risk of cardiovascular disease, the leading cause of death among the elderly. This large study has conflicting findings, as the author claims that the present analyses do not demonstrate protection against mortality from light-to-moderate drinking. In this study, what were termed “occasional drinkers,” rather than nondrinkers, were used as the comparison group.

Forum members had two main concerns about this study that warrant an investigation of the author’s conclusions: there was no consideration of under-reporting of alcohol intake when declaring “occasional drinkers” as the referent group, and (2) the inclusion, and adjusting for as “confounders,” several factors that are actually mechanisms by which alcohol has been shown to reduce mortality.

The first concern could have led to many light drinkers being included in the referent group, and thus not evaluated for a potential protective effect of light drinking on mortality. In fact, presented only in the Appendix to the paper are data showing that when nondrinkers make up the referent group, consumers of 1-7 as well as 7-14 drinks per week show significant 20-30% reductions in the risk of mortality; these findings are very similar to those of most previous epidemiologic studies.

The second, and perhaps more important concern, is that some of the mechanisms by which moderate alcohol intake may lead to lower mortality, such as reducing the risk of diabetes and coronary heart disease, were “adjusted” for in the analyses. This would attenuate or even erase any true reduction in risk of mortality from moderate drinking.

Some Forum members also were concerned that some subjects were missing data on alcohol consumption but, rather than excluding them, an estimated value was imputed for them. Further, data on the pattern of drinking (regular moderate versus binge drinking) or on the type of beverage consumed were not included in the evaluation.

Forum members conclude that the results of this study will obviously be considered in conjunction with other scientific data when seeking to judge the relation of alcohol intake to mortality. However, concerns about the analysis raise questions about the conclusion of the author of no protective effect of alcohol on mortality, a finding that conflicts with the results of most previous studies.

Reference: Goulden R. Moderate Alcohol Consumption Is Not Associated with Reduced All-cause Mortality. Am J Med 2015; pre-publication.

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