Adolescent IQ and risk of dementia: a 67-year prospective study

BACKGROUND: Early-life IQ is a consistent predictor of overall late life health, but its association with the risk of dementia is inconclusive. The present study examined the association between IQ in adolescence and the risk of all-cause dementia in older adulthood. METHODS: Participants (N = 3498) from the Wisconsin Longitudinal Study completed measures of IQ and demographic factors at about age 18 (1957) and were screened for dementia at about age 81 (2019-2024). Education and history of diabetes, hypertension, and smoking were tested as potential mediators. RESULTS: At the 67 years follow-up assessment, 378 participants (11%) had dementia. Higher IQ at 18 was associated with a lower risk of all-cause dementia (Odds ratio [OR] per one-SD increase in IQ= 0.78; 95% confidence interval [95% CI]= 0.69-0.88) at age 81. The association was similar when adolescent IQ was considered as a categorical variable that contrasted the top versus bottom quartiles (OR = 0.59; 95% CI = 0.43-0.81, p < .01). The association persisted controlling for demographic factors, was partially accounted for by the potential mediators (education, clinical and behavioral covariates), and was not moderated by sex or childhood socioeconomic status. CONCLUSIONS: Adolescent IQ is an early life factor associated with a lower risk of dementia in older adulthood. This research highlights the importance of a life-course perspective on brain health.