Childhood Cognitive Ability and Incident Dementia: The 1932 Scottish Mental Survey Cohort into their 10th Decade

Background: The prevention of dementia is a global priority but its aetiology is poorly understood. Early life cognitive ability has been linked to subsequent dementia risk but studies to date have been small and none has examined sex differences. Methods: In the 1932 Scottish Mental Survey cohort, we related intelligence test scores at age 11 years in 16,370 boys and 16,097 girls (born in 1921) to incident dementia aged ≥65 years as ascertained using probabilistic linkage to electronic health records up to the age of 92 years (1231 cases in men, 2163 in women; median follow up 15 years). Results: Compared to the highest intelligence group (≥115), dementia risk was raised in the lowest-scoring category (<85) and these effects were stronger for women (hazard ratio; 95% confidence interval: 1.51, 1.29 to 1.76) than men (1.19, 0.98 to 1.44; P-value for interaction by gender: 0.054). There was evidence of a dose-response association between childhood IQ and dementia in women (IQ 100-114.9 compared to ≥115: 1.18, 1.03 to 1.34; IQ 85-99.9: 1.32, 1.15 to 1.51; P-value for trend<0.001) but not in men (1.05, 0.89 to 1.24; 1.01, 0.85 to 1.21; 0.44) Conclusions: Childhood intelligence is related to subsequent dementia risk but this association is not the same in men and women.