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Critique 169: Effects of IQ on risk of morbidity and mortality related to alcohol consumption — 25 August 2015

The present paper is based on a large cohort of subjects in Sweden who had IQ tests as children (when they were 13 years old) and were then followed for more than 30 years. The study reports an inverse association between childhood IQ and hospitalization for alcohol-related diseases or death. The association is strongly dose-dependent, with a marked increase in disease/mortality risk for each decrease in the childhood IQ score.

A key finding in this analysis is that the attained socio-economic status (SES) of the subjects at age 32 played a large role in explaining the association between IQ and alcohol-related disease and appeared to completely explain the association with death from alcohol-related causes. This suggests that much of the effect of IQ during childhood may be through its effect on later education, occupation, and income of the subjects, associations that have been noted in many previous epidemiologic studies to favor better health. It is reassuring that being born into a poor, uneducated family is not as important as a determinant of adverse effects of alcohol later in life as is the attained socio-economic status of the individual in young adulthood.

A possible explanation for the inverse relation of SES in young adulthood with adverse alcohol outcomes could relate to the type of beverage consumed, which was not evaluated in the present analysis. In a previous study from Denmark, it was shown that higher SES in young adults was associated with a strong preference for wine rather than for other types of alcoholic beverage. Wine consumption has been associated with better health in numerous studies, although it is unclear whether this is due primarily to the non-alcoholic constituents in wine or to confounding from associated lifestyle factors of wine drinkers.

Forum members agree with the authors that the underlying causes for an association between IQ (or SES) and adverse alcohol-related disease and death are not clearly defined. It could be that intelligence has effects on health through choices in lifestyle behavior or socioeconomic environment as an adult, or the relationship between intelligence and health is confounded by other factors such as biological or socioeconomic conditions early in life. As for now, we can only describe the association, but not explain it fully.

Reference: Sjölund S, Hemmingsson T, Gustafsson JE, Allebeck P. IQ and alcohol-related morbidity and mortality among Swedish men and women: the importance of socioeconomic position. Journal of Epidemiology and Community Health 2015;69:858-864.

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