Childhood IQ, social class, deprivation, and their relationships with mortality and morbidity risk in later life: prospective observational study linking the Scottish Mental Survey 1932 and the Midspan studies.

Objective: To investigate how childhood mental ability (IQ) is related to mortality and morbidity risk, when socioeconomic factors are also considered.
Methods: Participants were from the Midspan studies conducted on adults in the 1970s; 938 Midspan participants were successfully matched with the Scottish Mental Survey 1932 in which children born in 1921 and attending Scottish schools on June 1, 1932, took a cognitive ability test. Mortality, hospital admissions, and cancer incidence in the 25 years after the Midspan screening were investigated in relation to childhood IQ, social class, and deprivation.
Results: The risk of dying in 25 years was 17% higher for each standard deviation disadvantage in childhood IQ. Adjustment for social class and deprivation category accounted for some, but not all, of this higher risk, reducing it to 12%. Analysis by IQ quartile showed a substantial increased risk of death for the lowest-scoring quarter only. Structural equation modeling indicated that the effect of childhood IQ on mortality was partly indirectly influenced by social factors. Cause-specific mortality or hospital admission showed that lower IQ was associated with higher risks for all cardiovascular disease and coronary heart disease. Cause-specific mortality or cancer incidence risk was higher with decreasing IQ for lung cancer.
Conclusions: Lower childhood IQ was related to higher mortality risk and some specific causes of death or morbidity. Childhood IQ may be considered as a marker for risk of death or illness in later life in similar and complementary ways to social class or deprivation category.