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Low IQ second strongest predictor of heart disease

Only smoking is a stronger predictor of cardiovascular risk than low intelligence

OnMedica staff

Wednesday, 10 February 2010

Lower intelligence scores were associated with higher rates of cardiovascular disease and total mortality at a greater level of magnitude than found with any other risk factor except smoking, in a large study published this week.

The study, funded by the Medical Research Council, is the first to compare the relative strength of the known association between intelligence scores and risk of cardiovascular disease with other established risk factors such as obesity, smoking and high blood pressure.

The West of Scotland Twenty-07 Study is a population study designed to investigate the influence of social factors on health. In 1987, a cohort of 1145 men and women, about 55 years old, had their height, weight, blood pressure, smoking habits, physical activity, education and occupation recorded; their cognitive ability (IQ) was assessed using a standard test of general intelligence. The participants were followed up for 20 years.

Researchers analysed these data using a statistical model to quantify the associations of nine risk factors with cardiovascular mortality. This revealed that the most important was cigarette smoking, followed by low IQ. Similar results were apparent when the health outcome was total mortality.

The study authors measured the relative strengths of the associations by an ‘index of inequality’. This summarised the relative risk of a health outcome (cardiovascular death) in the most disadvantaged (high risk) people relative to the most advantaged (low risk). This relative index of inequality for the top five risk factors was found to be 5.58 for cigarette smoking, 3.76 for IQ, 3.20 for low income, 2.61 for high systolic blood pressure, and 2.06 for low physical activity.

The investigators considered ways in which lower IQ scores could increase cardiovascular disease risk, notably the application of intelligence to healthy behaviour (such as smoking or exercise). A further possibility, they add, “is that IQ denotes ‘a record’ of environmental insults” such as illness or poor nutrition throughout life.

Dr Batty, the lead investigator, said that IQ could be one important factor behind the reason for social class being a fundamental determinant of inequalities in health. Traditionally, he said, explanations for such socioeconomic gradients in health have focused on access to resources (such as education and income), physical exposures at home and at work (such as housing conditions and toxins), and health-related behaviours (such as smoking and diet).

But studies show that such factors do not fully explain class-based differentials in health. A low IQ, he explained, may be a further independent explanation.

Fotini Rozakeas, cardiac nurse for the British Heart Foundation, said: “This study shows that IQ may be a factor in determining vulnerability to heart and circulatory disease particularly in lower socioeconomic groups. However, heart disease is largely preventable and many of the risk factors the study considered, such as smoking, physical inactivity, and high blood pressure, are ones we can all do something about.

“By making lifestyle changes such as stopping smoking, doing regular physical activity and eating a healthy balanced diet we can significantly reduce our risk of heart disease.

“In order to make real progress on tackling health inequalities we need health promotion campaigns designed to reach everyone in the community and encourage people to make healthy choices in food.”

The study, funded by the Medical Research Council, appears in the February issue of the European Journal of Cardiovascular Prevention and Rehabilitation.
Eur J Cardiovasc Prev Rehabil 2010, 17:24–7

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