Increased childhood intelligence scores are associated with a lower risk of mortality caused by coronary heart disease, stroke, cancers related to smoking, respiratory diseases, digestive diseases, injury, and dementia, according to data published in the BMJ.
Catherine M Calvin, PhD, from the Department of Psychology at the University of Edinburgh, United Kingdom, and colleagues conducted a prospective cohort study including mortality data from 33,535 men and 32,229 women born in Scotland in 1936 across 68 years of follow-up.
The researchers found that childhood intelligence was inversely associated with all major causes of mortality. The hazard ratios (HRs) for 1 SD advantage (about 15 points) in the intelligence test score were strongest for respiratory disease (0.72), coronary heart disease (0.75), and stroke (0.76). In addition, the investigators observed associations between childhood intelligence scores and deaths from injury (HR, 0.81), smoking-related cancers (HR, 0.82), digestive disease (HR, 0.82), and dementia (HR, 0.84).
Childhood intelligence scores were also related to some cancer presentations, including lung (HR, 0.75), stomach (HR, 0.77), bladder (HR, 0.81), esophageal (HR, 0.85), liver (HR, 0.85), colorectal (HR, 0.89), and hematopoietic (HR, 0.91). The results also showed weak associations between childhood intelligence scores and suicide (HR, 0.87) and deaths from cancers not related to smoking (HR, 0.96).
The investigators note that childhood intelligence was somewhat more strongly related to coronary heart disease, smoking-related cancers, respiratory disease, and dementia in women than in men.
The researchers also conducted a sensitivity analysis on a subsample of the study population, which revealed a 10% to 26% attenuation of the estimated effect of intelligence after adjustments, including 3 indicators of childhood socioeconomic status. Smoking and adult socioeconomic status also attenuated the association of intelligence with mortality rates by about 16% to 58% in a replication sample with a similar birth-year cohort and follow-up period.
“We have been able to report on the strength of association between premorbid intelligence and a range of specific causes of death in a full population and with follow-up from childhood to near the end of the life course,” the study authors noted. “The specialty of cognitive epidemiology remains in a growth period; therefore it is premature to make recommendations to practitioners and policymakers.
“Although we report that smoking and socioeconomic status are unlikely to fully mediate the observed associations, future studies would benefit from measures of the cumulative load of such risk factors over the life course.”
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