New research indicates that IQ is among the strongest predictors of cardiovascular disease and is second only to cigarette smoking in large population study.
The study, funded by Britain's Medical Research Council, has discovered that lower intelligence scores are associated with higher rates of cardiovascular disease and total mortality.
The findings of the study have appeared in the February issue of the European Journal of Cardiovascular Prevention and Rehabilitation.
These conclusions have been derived from the West of Scotland Twenty-07 Study, a population study designed to investigate the influence of social factors on health.
The present analysis was based on data collected in 1987 in a group of 1145 men and women aged around 55 and followed up for 20 years. Figures were collected for height, weight, blood pressure, smoking habits, physical activity, education and occupation; cognitive ability (IQ) was measured using a standard test of general intelligence.
When the data were applied to a statistical model to quantify the associations of nine risk factors with cardiovascular mortality, results showed that the most important was cigarette smoking, followed by low IQ. Similar results were noticed when the health outcome was total mortality.
The relative strengths of the association were assessed by an "index of inequality", which 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 study team noted "a number of plausible mechanisms" whereby lower IQ scores could increase cardiovascular disease risk, particularly the application of intelligence to healthy behaviour (such as smoking or exercise) and its correlates (obesity, blood pressure). A further possibility, they added, "is that IQ denotes 'a record' of environmental insults" (eg, illness, sub-optimal nutrition) accumulated throughout life.
The study's principal investigator Dr David Batty said: "From a public health perspective, there is the possibility that IQ can be increased, with some mixed results from trials of early learning and school readiness programmes.
"It may also be worthwhile for health promotion campaigns to be planned with consideration of individual cognition levels."