Intelligence Predicts Health and Longevity, but Why?

Intelligence Predicts Health and Longevity, but Why?

Large epidemiological studies of almost an entire population in Scotland have found that intelligence (as measured by an IQ-type test) in childhood predicts substantial differences in adult morbidity and mortality, including deaths from cancers and cardiovascular diseases. These relations remain significant after controlling for socioeconomic variables. One possible, partial explanation of these results is that intelligence enhances individuals’ care of their own health because it represents learning, reasoning, and problem-solving skills useful in preventing chronic disease and accidental injury and in adhering to complex treatment regimens.

A Gottfredson pdf just full of useful bits of information about the influence of IQ on mortality. A few of the most interesting bits…

a drop of 1 standard deviation in IQ was associated with a 27% increase in cancer deaths among men and a 40% increase in cancer deaths among women (Deary, Whalley, & Starr, 2003). The effect was especially pronounced for stomach and lung cancers, which are specifically associated with low socioeconomic status (SES) in childhood.

For each standard deviation increase in IQ, there was a 33% increased rate of quitting smoking. Adjusting for social class reduced this rate only mildly, to 25%. Thus, childhood IQ was not associated with starting smoking (mostly in the 1930s, when the public were not aware of health risks), but was associated with giving up smoking as health risks became evident.

When all other variables were statistically controlled, each additional IQ point predicted a 1% decrease in risk of death. Also, IQ was the best predictor of the major cause of death, motor vehicle accidents. Vehicular death rates doubled and then tripled at successively lower IQ ranges (100–115, 85–100, 80–85; O’Toole, 1990).

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A low IQ increases the risk of heart attack

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

Objective
To compare the strength of the association between intelligence quotient (IQ) and cardiovascular disease (CVD) mortality with the predictive power for established risk factors.

Design
Population-based cohort study of 1145 men and women with IQ test scores, a range of established risk factors, and 20-year mortality surveillance.

Results
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.

Conclusion
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.