Does IQ affect cardiovascular disease risk?

IQErr, well, maybe.  IQ does seem to account for some of the well-documented relationship between socioeconomic status and cardiovascular risk, according to new research in European Heart Journal.  Simply put, being more intelligent could be one reason why people from a high socioeconomic background are less likely to die from cardiovascular disease than those who are more disadvantaged.

The authors of this study wanted to unravel how low socioeconomic status leads to cardiovascular disease and poor health.  Factors like access to resources (e.g. education and income) and environmental exposures (e.g. housing conditions) have a role, but taking account of these factors in calculations – effectively eliminating their influence – doesn’t level the playing field, meaning that there must be some other elements at play.

Previous studies have shown that IQ is inversely correlated with total mortality and cardiovascular mortality – that is, people with a high IQ are at least risk of death from any cause and death from heart disease.

Batty et al. looked at data from 4,289 male former US soldiers to establish the extent to which IQ ‘explains’ socioeconomic disparities in health.  All participants took a general aptitude test when they joined the army between 1965 and 1971.  Results from this test, as well as data on their income at 20 years of age, were combined with IQ, health and financial data gleaned from a telephone survey when the participants were on average 38 years old.

As expected, men who had a high IQ – both at 20 years old and at middle age – tended to have more favourable social circumstances, such as higher family income, than those with a lower IQ.

In a second analysis, socioeconomic status was inversely associated with total mortality, cardiovascular mortality and death from any cause.  For example, men with a low current income or little education were more than six times more likely and three times more likely, respectively, to die from cardiovascular disease.

When the calculations were adjusted to take into account IQ scores at 20 years old, the huge differences in cardiovascular mortality between those who were well off and those who were less fortunate shrunk by a third; the disparity was reduced by more than half when IQ score at middle age was added instead.

Adjusting for other risk factors for cardiovascular disease – such as blood pressure and cholesterol level – had less of an effect on the mortality differences between the most fortunate and the least fortunate, suggesting that IQ has more of an effect on risk of cardiovascular disease according to socioeconomic status than do traditional risk factors.

The implication of this study is that efforts directed at reducing socioeconomic disadvantage to improve health should also include educational opportunities as well as improving housing and so on.
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Batty G et al. (2009) Does IQ explain socio-economic differentials in total and cardiovascular disease mortality? Comparison with the explanatory power of traditional cardiovascular disease risk factors in the Vietnam Experience Study. European Heart Journal 30 (15): 1903-1909. DOI: 10.1093/eurheartj/ehp254

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3 Comments

  1. Thanks for the comments guys.

    The authors do mention the interesting difference between the analysis using IQ at 20 years old and the analysis using IQ at middle age. They suggest two possibilities to account for this difference:
    1) That IQ is, to a degree, a ‘record of bodily insults across the life course’. Apparently IQ scores are inversely correlated with chronic disease, so tend to fall as a person ages and acquires more diseases. The authors tried to account for this possibility by excluding deaths in the first 4 years of follow-up, reasoning that those dying from chronic disease during this period were likely to have the highest amount of comorbidities at study induction, but controlling for this factor didn’t really change their results.
    2) That IQ at middle age is more likely to correspond with socioeconomic position than IQ at 20 years old – that is, 20 year olds haven’t had much opportunity to establish or change their socioeconomic position compared to older people.

    This study used serveral markers to determine socioeconomic position: income, education, family income, and ‘occupational prestige’ (don’t ask me how they worked out that one). So in theory this analysis would have taken into account ‘stress associated with subordination’ in the occupational prestige measure. Possibly. Health effects of IQ is certainly a murky area of study…

  2. As far as I can tell from this summary, the study used income as a measure of socioeconomic status (education was mentioned too but how it played out in the analysis isn’t clear from this). This might be a problem if we are interested in knowing whether or how the effect of IQ on risk is socially mediated. My impression from a cursory knowledge of the social determinants of health literature is that the big risk factor is stress associated with subordination rather than low income per se. Perhaps higher IQ individuals were, controlling for income (and formal education for that matter), more likely to be positions or occupations that afforded them greater autonomy and (self) respect. We would also ideally want to factor in variables that could both depress IQ scores and and contribute to cardiovascular risk. Poverty and other stressors in childhood could play a role here.

  3. Interesting article. IQ scores tend to be pretty stable after age 8, so I’m wondering first about the differences when IQ at 20 versus middle age are added into the equation. If those IQ scores are significantly different, I would question the measures they are using. In addition, the recommendation to include educational opportunities will probably increase achievement scores, but changing IQ scores tends to take significant long term intervention. Thanks for the summary.

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