Greater intelligence may in part partially explain why people from a high socio-economic background live longer than those of lower social status, researchers have suggested.

A study of former soldiers in the United States has indicated that differences in IQ may explain almost a quarter of the differences in mortality between people of higher and lower social classes.

It has long been accepted that social status affects mortality, with a particular influence on death from cardiovascular events such as strokes and heart attacks. Many of these differences have been ascribed to stress, to income, and to behavioural factors such as smoking and diet — but these cannot explain the whole gap in longevity between the highest socio-economic groups and the lowest ones.

The new study, from a team led by David Batty, of the MRC Social and Public Health Sciences Unit at the University of Glasgow, compared outcomes from a group of 4,289 former American soldiers drawn from diverse social backgrounds.

It found that variations in IQ explain about 23 per cent of the survival differences between different social groups. Details of the study are published in European Heart Journal.

Professor Sir Michael Marmot, of University College, London, who leads the Whitehall II study of civil servants, which has uncovered many of the effects of social class on mortality, and his colleague Mika Kivimaki, offered three possible explanations for the effect in a commentary for the journal.

“Intelligence might lead to greater knowledge about how to pursue healthy behaviours,” he wrote. Intelligence may “cause” socio-economic position; that is, more intelligence leads to more education, and greater income and occupational prestige. “Intelligence may be a marker for something else, and it is that something else, early life exposures, for example, that leads to mortality,” Dr Batty said.

“We already know that socio-economically disadvantaged people have worse health and tend to die earlier from conditions such as heart disease, cancer and accidents. Environmental exposures and health-related behaviours, such as smoking, diet and physical activity, can explain some of this difference, but not all of it. This raises the possibility that as-yet-unmeasured psychological factors need to be considered. One of these is intelligence or cognitive function, commonly referred to as IQ. This measures a person’s ability to reason and problem-solve. IQ is strongly related to socio-economic status.

“IQ wasn’t a magic bullet in this study, but this psychological variable had additional explanatory power on top of the classic variables such as smoking, high blood pressure, high blood glucose and obesity. It has partially explained the differences in death from heart disease and all causes.”

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