Does IQ predict total and cardiovascular disease mortality as strongly as other risk factors? Comparison of effect estimates using the Vietnam Experience Study
- 1MRC Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK
- 2MRC Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, Edinburgh, UK
- 3Department of Epidemiology and Public Health, University College London, London, UK
- 4MRC Epidemiology Resource Centre, University of Southampton, Southampton, UK
- 5National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark
- 6Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina, USA
- Dr G D Batty, MRC Social and Public Health Sciences Unit, University of Glasgow, 4 Lilybank Gardens, Glasgow G12 8RZ, UK;
- Accepted 30 July 2008
- Published Online First 18 September 2008
Objective: To compare the strength of the relation of two measurements of IQ and 11 established risk factors with total and cardiovascular disease (CVD) mortality.
Methods: Cohort study of 4166 US male former army personnel with data on IQ test scores (in early adulthood and middle age), a range of established risk factors and 15-year mortality surveillance.
Results: When CVD mortality (n = 61) was the outcome of interest, the relative index of inequality (RII: hazard ratio; 95% CI) for the most disadvantaged relative to the advantaged (in descending order of magnitude of the first six based on age-adjusted analyses) was: 6.58 (2.54 to 17.1) for family income; 5.55 (2.16 to 14.2) for total cholesterol; 5.12 (2.01 to 13.0) for body mass index; 4.70 (1.89 to 11.7) for IQ in middle age; 4.29 (1.70 to 10.8) for blood glucose and 4.08 (1.63 to 10.2) for high-density lipoprotein cholesterol (the RII for IQ in early adulthood was ranked tenth: 2.88; 1.19 to 6.97). In analyses featuring all deaths (n = 233), the RII for risk factors most strongly related to this outcome was 7.46 (4.54 to 12.3) for family income; 4.41 (2.77 to 7.03) for IQ in middle age; 4.02 (2.37 to 6.83) for smoking; 3.81 (2.35 to 6.17) for educational attainment; 3.40 (2.14 to 5.41) for pulse rate and 3.26 (2.06 to 5.15) for IQ in early adulthood. Multivariable adjustment led to marked attenuation of these relations, particularly those for IQ.
Conclusions: Lower scores on measures of IQ at two time points were associated with CVD and, particularly, total mortality, at a level of magnitude greater than several other established risk factors.
Funding: The Medical Research Council (MRC) Social and Public Health Sciences Unit receives funding from the UK MRC and the Chief Scientist Office at the Scottish Government Health Directorates. The MRC and the University of Edinburgh provide core funding for the MRC Centre for Cognitive Ageing and Cognitive Epidemiology which supported this research. GDB and CRG are honorary fellows of the University of Edinburgh. GDB is a Wellcome Trust Fellow (WBS U.1300.00.006.00012.01). MJS is supported by the British Heart Foundation and LHM by the National Institute of Public Health, Denmark. Mortality surveillance of the cohort in the post-service Vietnam Experience Study was funded by the National Center for Environmental Health in Atlanta, USA.
Competing interests: None.
Ethics approval: The study protocol was passed by the US Office for Technology Assessment; the Department of Health and Human Sciences Advisory Committee; the Agent Orange Working Group Science Panel; and a review panel from the US Centers for Disease Control.