Childhood cognitive ability and lifetime cognitive change as predictors of midlife physical function: Results from the National Child Development Survey
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ABSTRACT Objective: To investigate possible mediators of the relationship between childhood general cognitive ability scores and cognitive ability change and adulthood physical function. Method: 5435 participants (2645 male, 2790 female) drawn from the National Child Development Survey provided data on childhood cognitive ability aged eleven, exercise frequency, smoker status, depression scores, Body Mass Index, general health and occupational and educational level aged forty-two and self-report physical function scores aged fifty. Mediation analyses tested the hypotheses that childhood cognitive ability and lifetime cognitive ability change would significantly predict being in the lowest sex-specific quintile of physical function scores and that the model would differ by sex. Logistic regressions provided odds ratios. Results: For men, childhood intelligence significantly predicted low physical function scores via general health, SES, depression and smoking status. Odds ratios for the lowest relative to highest general health rating was 8.42 (CI(95%) LB 4.27, UB 16.59). The highest SES group had an OR of 0.34 (CI(95%) LB 0.16, UB 0.74) relative to the lowest group. For a single score increase in depression the OR was 1.13 (CI(95%) LB 1.09, UB 1.20) and for exercise frequency 0.932 (CI(95%) LB 0.89, UB 0.98). When CA change was the predictor, depression was no longer a significant mediator (p=.17). The direct effect of intelligence disappeared after accounting for the indirect effects (childhood CA: p=.469, CA change: p=.82). In women, childhood CA significantly predicted midlife PF via all mediators except 5 exercise frequency and SES. This was the same when CA change was the predictor except smoker status became non-significant (p=.105). Odds ratios for 1SD increase in childhood CA was 0.85 (CI(95%) LB 0.76, UB 0.96), for BMI score 1.10 (CI(95%) LB 1.08, UB 1.12), and for depression score 1.10 (CI(95%) LB 1.07, UB 1.13). Current smokers were 1.40 times as likely as non-smokers (CI(95%) LB 1.09, 1.80). The lowest general health group had an odds ratio of 11.41 (CI(95%) LB 5.98, UB 21.77). The highest educated cut their risk to 0.34(CI(95%) LB .14, UB 0.86). The direct effects remained even after accounting for the indirect effects (childhood CA: β=-.183, p=.0024, CI(95%) LB -.301, UB -.065, 53.63% explained; CA change: β=-.395, p= , CI(95%) LB , UB, 33% explained). The results suggest that general intelligence and its decline are significant risk factors for developing low physical function in midlife via both health-related and socioeconomic variables.