TitleIntelligence and all-cause mortality in the 6-Day Sample of the Scottish Mental Survey 1947 and their siblings: testing the contribution of family background.
Publication TypeJournal Article
Year of Publication2018
AuthorsIveson, MH, Cukic, I, Der, G, Batty, GD, Deary, IJ
JournalInt J Epidemiol
Date Published02/2018
KeywordsAdult, Aged, Cause of Death, Cohort Studies, Family, Female, Humans, Intelligence, Intelligence Tests, Kaplan-Meier Estimate, Longevity, Male, Middle Aged, Risk Factors, Scotland, Siblings, Socioeconomic Factors

Background: Higher early-life intelligence is associated with a reduced risk of mortality in adulthood, though this association is apparently hardly attenuated when accounting for early-life socio-economic status (SES). However, the use of proxy measures of SES means that residual confounding may underestimate this attenuation. In the present study, the potential confounding effect of early-life SES was instead accounted for by examining the intelligence-mortality association within families.

Methods: The association between early-life intelligence and mortality in adulthood was assessed in 727 members of the 6-Day Sample of the Scottish Mental Survey 1947 and, for the first time, 1580 of their younger siblings. These individuals were born between 1936 and 1958, and were followed up into later life, with deaths recorded up to 2015. Cox regression was used to estimate the relative risk of mortality associated with higher IQ scores after adjusting for shared family factors.

Results: A standard-deviation advantage in IQ score was associated with a significantly reduced mortality risk [hazard ratio = 0.76, p < 0.001, 95% confidence interval (CI) (0.68-0.84)]. This reduction in hazard was only slightly attenuated by adjusting for sex and shared family factors [hazard ratio = 0.79, p = 0.002, 95% CI (0.68-0.92)].

Conclusions: Although somewhat conservative, adjusting for all variance shared by a family avoids any potential residual confounding of the intelligence-mortality association arising from the use of proxy measures of early-life SES. The present study demonstrates that the longevity associated with higher early-life intelligence cannot be explained by early-life SES or within-family factors.

Alternate JournalInt J Epidemiol
PubMed ID29025063
PubMed Central IDPMC5837228
Grant ListMC_UU_12017/13 / / Medical Research Council / United Kingdom
MR/K026992/1 / / Medical Research Council / United Kingdom