How well a person does on a standardized intelligence test -- in other words, their IQ score -- may be related to his or her risk for having a heart attack, according to a team of researchers who have been investigating the potential link between the brain and the heart.
In a study of more than 1,100 middle-aged Scottish men and women who were followed for 20 years, a low score on an IQ test was a better predictor of death from heart disease than traditional risk factors such as systolic blood pressure -- the first number in a blood pressure reading -- income, and lack of exercise. Only smoking topped low IQ as a predictor of death, according to G. David Batty, a researcher at the University of Glasgow.
Batty and his colleagues, who reported their observations in the European Journal of Cardiovascular Prevention and Rehabilitation, found a similar link when they studied Vietnam veterans.
The brain-heart link, they wrote, might reflect skills associated with intelligence, such as the ability to understand and act on advice about healthy lifestyles, Batty wrote.
However, these conclusions drew sharp criticism from leading American cardiologists.
IQ should not be factored into the equation for identifying high-risk patients or in initiating aggressive prevention strategies, cautioned Dr. Elizabeth Barrett-Connor of the University of California San Diego, who called the study a misleading grab for headlines.
The relationship with mortality is inescapably confounded, added Dr. Merle Myerson, director of Preventive Cardiology at St. Luke's-Roosevelt Hospital in New York.
"What goes along with lower IQ is generally lower socioeconomic status, lower access to medical care, lower awareness of risk factors -- diagnosis and treatment -- et cetera," she told ABC News and MedPage Today.
Dr. Steve Nissen, chair of Cardiovascular Medicine at the Cleveland Clinic, criticized the failure to adjust for these important factors that, for economic reasons, are more likely to accompany low IQ.
"This is bad research and has the potential to amplify damaging stereotypes," he said. "This 'research' is more about the inequalities of British and American societies than the virtues of being 'smart.'"
In the study, Batty's team studied 1,145 men and women who were 56 years old when the study started in 1986-87. All participants had IQ tests as part of an initial assessment of risk factors. The researchers also tracked traditional risk factors, which included systolic blood pressure -- considered a major risk factor for stroke and/or death from heart disease -- as well as physical activity, and smoking.
The research revealed that smokers had about a six-fold increase in 20-year risk of a fatal heart attack or stroke compared with non-smokers, while low intelligence was associated with close to a four-fold increase in risk compared with individuals with high IQ scores. By comparison, low income -- a well-recognized risk factor -- tripled the risk, while high systolic blood pressure increased risk about two and half times and being a couch potato appeared to double the relative risk of dying from heart disease.
When the authors looked at all cause mortality, smoking still trumped all other risk factors so that smokers had almost a five-fold risk of death over the 20-year study, but here again IQ that a potent predictor -- low IQ scores more than trebled the odds of death.
Batty and colleagues said it was likely that low IQ was simply a marker for unhealthy lifestyles, meaning that persons with lower intelligence might be more likely to smoke or to live sedentary lifestyles or fail to manage risk factors such as diabetes or high blood pressure.
But the cardiologists contacted by ABC News and MedPage Today all agreed that establishing a causal link between IQ and mortality -- a true association -- would be at best difficult and probably impossible.
Moreover, leading cardiologists pointed out that Batty and colleagues did not collect data on other important risk factors such as cholesterol, glucose levels in the blood (diabetes), and inflammatory markers -- all of which are usually included in an assessment of heart attack risk.