Does IQ predict cardiovascular disease mortality as strongly as established risk factors? Comparison of effect estimates using the West of Scotland Twenty-07 cohort study
To compare the strength of the association between intelligence quotient (IQ) and cardiovascular disease (CVD) mortality with the predictive power for established risk factors.
Population-based cohort study of 1145 men and women with IQ test scores, a range of established risk factors, and 20-year mortality surveillance.
When CVD mortality was the outcome of interest, the relative index of inequality (sex-adjusted hazard ratio, 95% confidence interval) for the most disadvantaged relative to the advantaged persons was (in descending order of magnitude for the top five risk factors): 5.58 (2.89, 10.8) for cigarette smoking; 3.76 (2.14, 6.61) for IQ; 3.20 (1.85, 5.54) for income; 2.61 (1.49, 4.57) for systolic blood pressure and 2.06 (1.07, 3.99) for physical activity. Mutual adjustment led to some attenuation of these relationships. Similar observations were made in the analyses featuring all deaths where, again, IQ was the second most powerful predictor of mortality risk.
In this cohort, lower intelligence scores were associated with increased rates of CVD and total mortality at a level of magnitude greater than most established risk factors.
There’s also a paper from 2008 by the same man that comes to a similar conclusion after studying 4,166 US soldiers. This one concluded
The main finding was that, in age-adjusted analyses, lower IQ scores in both early adulthood and middle age were related to total and CVD mortality at a level of magnitude greater than many traditional risk indices.
What I did find amusing was reading through what the media had to say on this recently, trying to tell people that they could boost IQ with education (hasn’t been done with any lasting effect yet, and many have tried).
Higher IQ has been associated with better outcome for disease in other studies, with explanations from following a healthier lifestyle (smokers have a much lower average IQ, 7.5 points lower) and being better able to manage medical conditions and medication.