Objective: Examine the relation between IQ in early adulthood and later coronary heart disease (CHD) mortality, and assess the extent to which established risk factors measured in middle-age might explain this gradient.
Design: Cohort study of 4316 male former Vietnam-era US army personnel with IQ scores (mean age 20.4 years), risk factor data (mean age 38.3 years) and 15 years mortality surveillance.
Results: In age-adjusted analyses, lower IQ scores were associated with an increased rate of CHD mortality (hazard ratio per SD decrease in IQ; 95% confidence interval: 1.34; 1.00, 1.79). Adjustment for later chronic disease (1.22; 0.91, 1.64), behavioural (1.29; 0.95, 1.74) and physiological risk factors (1.19; 0.88, 1.62) led to some attenuation of this gradient. This attenuation was particularly pronounced on adding socioeconomic indices to the multivariable model when the IQ-CHD relation was eliminated (1.05; 0.73, 1.52). A similar pattern of association was apparent when cardiovascular disease was the outcome of interest.
Conclusion: High IQ may lead to educational success, well remunerated and higher prestige employment, and this pathway may confer cardio-protection.