Childhood IQ and all-cause mortality before and after age 65: prospective observational study linking the Scottish Mental Survey 1932 and the Midspan studies.

OBJECTIVES The objective was to investigate how childhood IQ related to all-cause mortality before and after age 65. DESIGN The Midspan prospective cohort studies, followed-up for mortality for 25 years, were linked to individuals' childhood IQ from the Scottish Mental Survey 1932. METHODS The Midspan studies collected data on risk factors for cardiorespiratory disease from a questionnaire and at a screening examination, and were conducted on adults in Scotland in the 1970s. An age 11 IQ from the Scottish Mental Survey 1932, a cognitive ability test conducted on 1921-born children attending schools in Scotland, was found for 938 Midspan participants. The relationship between childhood IQ and mortality risk, adjusting for adulthood socio-economic confounders, was analysed. The effect of adjustment for childhood IQ on the relationship between established risk factors (blood pressure, smoking, height and respiratory function) and mortality was also investigated. RESULTS For deaths occurring up to age 65, there was a 36% increased risk per standard deviation decrease (15 points) in childhood IQ which was reduced to 29% after adjusting for social class and deprivation category. There was no statistically significant relationship between childhood IQ and deaths occurring after the age of 65. Adjustment for childhood IQ attenuated the risk factor-mortality relationship in deaths occurring up to age 65, but had no effect in deaths occurring after age 65. CONCLUSIONS Childhood IQ was significantly related to deaths occurring up to age 65, but not to deaths occurring after age 65.