Intelligence Test Scores Before and After Alcohol‐Related Disorders—A Longitudinal Study of Danish Male Conscripts

BACKGROUND: Existing studies on intellectual consequences of alcohol‐related disorders are primarily cross‐sectional and compare intelligence test scores of individuals with and without alcohol‐related disorders, hence mixing the influence of alcohol‐related disorders and predisposing factors such as premorbid intelligence. In this large‐scale study, the primary aim was to estimate associations of alcohol‐related disorders with changes in intelligence test scores from early adulthood to late midlife. METHODS: Data were drawn from a follow‐up study on middle‐aged men, which included a re‐examination of the same intelligence test as completed in young adulthood at military conscription (total analytic sample = 2,499). Alcohol‐related hospital diagnoses were obtained from national health registries, whereas treatment for alcohol problems was self‐reported at follow‐up. The analyses included adjustment for year of birth, retest interval, baseline intelligence quotient (IQ) score, education, smoking, alcohol consumption, and psychiatric and somatic comorbidity. RESULTS: Individuals with alcohol‐related hospital diagnoses (8%) had a significantly lower baseline IQ score (95.0 vs. 100.5, p < 0.001) and a larger decline in IQ scores from baseline to follow‐up (−8.5 vs. −4.8, p < 0.001) than individuals without such diagnoses. The larger decline in IQ scores with alcohol‐related hospital diagnoses remained statistically significant after adjustment for all the covariates. Similar results were revealed when IQ scores before and after self‐reported treatment for alcohol problems (10%) were examined. CONCLUSIONS: Individuals with alcohol‐related disorders have a lower intelligence test score both in young adulthood and in late midlife, and these disorders, moreover, seem to be associated with more age‐related decline in intelligence test scores. Thus, low mean intellectual ability observed in individuals with alcohol‐related disorders is probably a result of both lower premorbid intelligence and more intellectual decline.