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

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Abstract
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.