Intelligence quotient (IQ) in adolescence and later risk of alcohol-related hospital admissions and deathsu37-year follow-up of Swedish conscripts

Aims To investigate the relationship between intelligence measured at ages 1819 and later alcohol-related hospital admission and mortality among men, while controlling for possible confounders. Design Cohort study. Setting and participants A total of 49 321 Swedish men who were conscripted for military training in 1969-70 and followed until 2007. Measurements Intelligence quotient (IQ) measured at conscription is the exposure, while alcohol-related hospital admission and death are the two outcomes. Adjustments for following variables were made: early life circumstances [childhood socio-economic position (SEP), father's drinking], mental health, social adjustment and behavioural factors measured at age 18 (psychiatric diagnosis, contact with police and child care, low emotional control, daily smoking, risky use of alcohol) and adult social position (attained education, SEP and income at age 40). Findings IQ had an inverse and graded association with later alcohol-related problems. For alcohol-related hospital admissions the crude hazard ratio (HR) was 1.29 (95% CI = 1.26-1.31) and for alcohol-related mortality it was 1.21 (95% CI = 1.17-1.24) for every one point decrease on the nine-point IQ scale. Adjustment for risk factors measured at age 18 attenuated the association somewhat for both outcomes. After adjustment for social position as adult, the HR was considerably lower resulting in a HR of 1.06 (95% CI = 1.02-1.10) for alcohol-related hospital admissions and 1.01 (95% CI = 0.95-1.08) for alcohol-related mortality. Conclusions In Swedish men there is an association between IQ in early adulthood and later alcohol-related hospital admission and death. Social position as adult could be an important contributory factor.