The association of early IQ and education with mortality: 65 year longitudinal study in Malmö, SwedenBMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b5282 (Published 11 December 2009) Cite this as: BMJ 2009;339:b5282
- 1Centre for Health Equity Studies (CHESS), Stockholm University/Karolinska Institutet, Stockholm, Sweden
- 2Department for Public Health Sciences, Karolinska Institutet, Stockholm, Sweden
- 3Swedish National Institute of Public Health, Östersund, Sweden
- Correspondence to: A Lager
- Accepted 13 November 2009
Objectives To establish whether differences in early IQ explain why people with longer education live longer, or whether differences in father’s or own educational attainment explain why people with higher early IQ live longer.
Design Population based longitudinal study. Mortality risks were estimated with Cox proportional hazards regressions.
Setting Malmö, Sweden.
Participants 1530 children who took IQ tests at age 10 and were followed up until age 75.
Results Own educational attainment was negatively associated with all cause mortality in both sexes, even when early IQ and father’s education were adjusted for (hazard ratio (HR) for each additional year in school 0.91 (95% CI 0.85 to 0.97) for men and HR 0.88 (95 % CI 0.78 to 0.98) for women). Higher early IQ was linked with a reduced mortality risk in men, even when own educational attainment and father’s education were adjusted for (HR for one standard deviation increase in IQ 0.85 (95 % CI 0.75 to 0.96)). In contrast, there was no crude effect of early IQ for women, and women with above average IQ had an increased mortality risk when own educational attainment was adjusted for, but only after the age of 60 (HR 1.60 (95 % CI 1.06 to 2.42)). Adding measures of social career over and above educational attainment to the model (for example, occupational status at age 36 and number of children) only marginally affected the hazard ratio for women with above average IQ (<5%).
Conclusions Mortality differences by own educational attainment were not explained by early IQ. Childhood IQ was independently linked, albeit differently, to male adult mortality and to female adult mortality even when father’s education and own educational attainment was adjusted for, thus social background and own social career seem unlikely to be responsible for mortality differences by childhood IQ. The clear difference in the effect of IQ between men and women suggests that the link between IQ and mortality involves the social and physical environment rather than simply being a marker of a healthy body to begin with. Cognitive skills should, therefore, be addressed in our efforts to create childhood environments that promote health.
We thank Sonja Olin Lauritzen for giving us access to the Malmö Longitudinal Study data and Zenia Hellström and Sofia Sandgren for practical help.
Contributors: The study was based on ideas by AL, SB, and DV. AL conducted the data analyses and drafted the first version of the article. SB and DV revised the first draft. All authors have read and approved the final version, have had full access to all data (including intermediate statistical reports and tables), and take responsibility for the integrity of the data and the accuracy of the data analysis. All authors are guarantors for the study.
Funding: The Swedish Council for Working Life and Social Research financed the updating of the Malmö Longitudinal Study database. AL and SB were funded by the Swedish National Institute of Public Health. The funders had no role in the collection, analysis, and interpretation of the data; the writing of the article; or the decision to submit the article for publication.
Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: (1) No financial support for the submitted work from anyone other than their employer; (2) No financial relationships with commercial entities that might have an interest in the submitted work; (3) No spouses, partners, or children with relationships with commercial entities that might have an interest in the submitted work; (4) No non-financial interests that may be relevant to the submitted work.
Ethical approval: The study was approved by the regional ethics board of Stockholm, Sweden (no 2007/1090-31).
Data sharing: The original data and statistical code have been saved for review purposes and future secondary analyses, and can be requested from the corresponding author at.
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