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Critique 178: The association of alcohol intake with health-related quality of life

Many studies have shown that moderate alcohol drinkers tend to have higher ratings of their quality of life (QOL) than non-drinkers. The directionality of this association has been difficult to ascertain: does moderate drinking improve someone’s QOL, or do people with higher QOL to begin with tend to drink alcohol moderately? The present study attempts to provide data designed to evaluate the directionality of these associations for both physical aspects of QOL as well as mental aspects.

Forum reviewers considered this to be a very well-done study from the Nurses’ Health Study II, with excellent and repeated measurements of both alcohol consumption and indices of QOL. It deals with the assessment of both physical and mental aspects of quality of life as well as the directionality of such an association: subjects were repeatedly assessed for the effects of alcohol intake on subsequent QOL as well as the effects of a given QOL measure on subsequent alcohol intake.

The key reported findings of this study were a positive association between alcohol and subsequent indices of physical QOL indices, with the poorest outcomes in abstainers and former drinkers; in spline analyses, the favorable effect appears to be up to about 2 drinks/day. Subjects with higher physical QOL also appeared to consume more alcohol in subsequent assessments. Somewhat surprising was the finding of little relation between alcohol and mental aspects of QOL, and even an apparent deleterious effect at the highest category of drinking. Thus, the study reports that physical aspects of QOL are positively associated with alcohol consumption, while mental aspects show little relation.

There was some concern by some Forum members about the methods used by the authors in adjusting, or not adjusting, for previous exposures (both alcohol and indices of QOL). Given that both baseline alcohol intake and QOL measures may tend to remain rather static over the period of the study (this “prevalent” exposures), adjusting for the effects of baseline values could attenuate any effect seen on subsequent outcomes. For example, if alcohol consumption indeed affects QOL and consumption remains roughly the same over the time period of the study, any effect of subsequent alcohol on QOL may be subsumed by the effects shown at baseline. In that situation, the net effect of adjustment for baseline alcohol may attenuate (or remove) the effect of the follow-up exposure on the outcome variable. The authors of this paper were aware of this problem, and attempted to deal with it. However, from the data presented, it is not possible to ascertain the specific analytic procedures used, and the final estimates of effect given for alcohol and QOL may still be biased.

Overall, the Forum considers this to be an important contribution to our understanding of how alcohol consumption may affect quality of life, and how quality of life affects alcohol consumption. As interpreted by the authors, physical aspects of QOL may be positively affected by alcohol consumption, but there is little effect on mental aspects of QOL.

Reference: Schrieks IC, Wei MY, Rimm EB, Okereke OI, Kawachi I, Hendriks HFJ, Mukamal KJ. Bidirectional associations between alcohol consumption and health-related quality of life amongst young and middle-aged women. J Intern Med 2015, pre-publication. doi:10.1111/joim.12453.

 

For the full critique of this paper by members of the International Scientific Forum on Alcohol Research, please click here.
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