Intelligence in early adulthood and subclinical atherosclerosis in middle-aged men: the Vietnam Experience Study

BACKGROUND: People with higher intelligence in early life have a lower subsequent risk of coronary heart disease events, but the explanation for these observations is unclear. AIMS: To examine whether intelligence in early adulthood is associated with risk of subclinical atherosclerosis in mid-life, as indicated by the ankle brachial index (ABI), and investigate its potential mediating role in the association between intelligence and mortality. METHODS: Participants were 4286 male US veterans whose intelligence was measured on enlistment into military service at a mean age of 20.4 years and whose ABI was measured by Doppler as part of a detailed medical examination at a mean age of 38.3 years. RESULTS: Higher intelligence in early adulthood was associated with a higher ABI in mid-life. For an SD increase in intelligence, after adjusting for age, ABI (× 10) rose by 0.05 (0.02, 0.07), and the OR (95% CI) for having a low ABI (≤ 0.90) was 0.84 (0.72 to 0.98). Further adjustment for smoking, serum cholesterol, triglycerides and glucose concentrations, blood pressure, erythrocyte sedimentation rate, body mass index, alcohol intake, education and measures of socioeconomic position had little or no attenuating effect on these associations. Lower ABI was associated with increased mortality from all causes and cardiovascular disease but it did not account for the associations between IQ and mortality from these causes. CONCLUSIONS: Men of lower intelligence may be more susceptible to atherogenesis, though this mechanism does not appear to explain their increased risk of earlier death.