IQ in late adolescence/early adulthood, risk factors in middle age, and later cancer mortality in men: the Vietnam Experience Study.

OBJECTIVES

(i) examine the relation, if any, of pre-morbid IQ scores at 20 years of age with the risk of later cancer mortality; and (ii) explore the role, if any, of potential mediating factors (e.g. smoking, obesity), assessed in middle age, in explaining the IQ-cancer relation.

METHODS

Cohort study of 14, 491 male, Vietnam-era, former US army personnel with IQ test scores at around 20 years of age (1965-71), who participated in a risk factor survey at around age 38 years of age (1985-6), who were then followed up for mortality experience for 15 years.

RESULTS

There were 176 cancer deaths during mortality surveillance. We found an inverse association of IQ with later mortality from all cancers combined (age-adjusted HR(per one SD decrease in IQ); 95% confidence interval: 1.27; 1.10, 1.46) and smoking-related malignancies (1.37; 1.14, 1.64). There was some attenuation following control for mediating variables, particularly smoking and income, but the gradients generally held at conventional levels of statistical significance.

CONCLUSIONS

Higher scores on pre-morbid IQ tests are associated with lower risk of later cancer morality. The strength of the relation was partially mediated by established risk factors.