Err, 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.
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