IQ and disparities in heart disease

Differences in IQ may be one reason that lower-income individuals are more likely to die of heart disease than their more affluent counterparts.

It is well known that people with less education and lower incomes generally face higher risks of a range of diseases. Past studies have pointed to many likely reasons - including less access to healthcare and other resources, poorer living conditions, chronic stress and higher rates of lifestyle risk factors, like smoking and physical inactivity.

However, these factors do not seem to fully explain the disparities. Therefore, researchers studied 4,289 American men to examine the relationship between intelligence quotient (IQ) and the risk of dying from heart disease or stroke. The men were given intelligence tests when they entered the Army during the Vietnam War and were tested again during middle age. Over the following 15 years, 62 study participants died of heart disease.

It was found that men from the lowest economic status - measured by income, occupation and education - were between two and seven times more likely to die of causes related to heart disease than the most advantaged men. Risk factors, including high blood pressure, smoking and obesity, explained about 40 percent of the disparity. But IQ itself also appeared to play a role, explaining another quarter of the socioeconomic gap.

IQ may essentially serve as an index of environmental insults accumulated across the lifetime, including illnesses, chronic stress and unhealthy lifestyle habits. It was supported by the finding that IQ during middle age was more strongly connected to cardiovascular risks than IQ in young adulthood was.

The researchers concluded that among socio-economic ingredients in cardio-vascular disease mortality, IQ appeared to offer higher explanatory power than that apparent for traditional cardio-vascular risk factors.