Background: People who score poorly in intellectual ability tests have shorter life expectancy. We studied whether this association is different in people from different socio-economic backgrounds.
Methods: We studied the mortality of 2786 men born in Helsinki, Finland, during 1934-44, who as military conscripts underwent a standardised intellectual ability test comprising verbal, visuospatial and arithmetic reasoning subtests. Mortality data came from the Finnish Death Register.
Results: Comparing men in the lowest and highest test score fourths, hazard ratios for all-cause mortality were 1.9 (95% confidence interval 1.4-2.5) for verbal, 2.2 (1.6-3.0) for visuospatial and 1.9 (1.4-2.5) for arithmetic reasoning, corresponding to 2.6, 3.4 and 2.6 excess years of life lost, respectively. Associations were similar for cardiovascular and non-cardiovascular mortality. Intellectual ability scores were stronger predictors in men who grew up in middle class families. Compared with middle class men in the highest fourth of visuospatial reasoning score, middle class men in the lowest fourth lost 6.5 years of life, while men from manual workers- families in the highest fourth lost 2.8 years and men in the lowest fourth lost 5.6 years.
Conclusions: High intellectual ability in men aged 20 protects from mortality in later life. This effect is stronger in men who grew up in middle class as compared with manual workers- families. We suggest that early life conditions that are unfavourable to development of cognitive abilities negate the life expectancy benefits of being born into a more affluent family.
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