People who had greater intellectual ability as children may have fewer heart disease risk factors in middle-age, a new study suggests.

A number of studies have linked higher childhood IQ to better adulthood health and a longer life, but the reasons have not been entirely clear.

For example, early environment -- starting in the womb -- may affect both a child's intellectual ability and long-term disease risks. On the other hand, childhood ability also affects a person's chances of getting a good job or adopting a healthy lifestyle in adulthood.

These latest findings, published in the American Journal of Public Health, suggest that childhood intelligence indirectly affects long-term heart health -- mostly by influencing a person's education, job and health habits in adulthood.

For the study, researchers led by Dr. Chris Power of University College London in the UK analyzed data from 9,377 British adults who had been followed since their birth in 1958. At age 11, participants had taken tests of general intelligence and math and verbal ability. Their heart disease risk factors -- including obesity and elevated blood pressure, blood sugar and cholesterol -- were measured at age 45.

Overall, Power's team found, there was a correlation between childhood general intelligence and blood pressure, blood sugar and weight in adulthood -- though the effects were modest. For example, for each standard-deviation increase in test scores, systolic blood pressure (the top number in a blood-pressure reading) dipped by about a half-point.

The researchers then looked at a number of factors that could explain the association, including childhood social class -- based on the father's job -- and birthweight, which may affect both child development and adult health.

But accounting for those early-life factors did little to affect the association between childhood intelligence and later heart health.

In contrast, when the researchers factored in adulthood health habits, education and job attainment by age 42, the links between childhood intelligence and the various heart risk factors weakened substantially or disappeared altogether.

Adulthood lifestyle habits -- including whether participants smoked, exercised regularly or opted for fruits and vegetables over fish-and-chips -- were particularly important, the study found.

The researchers note that childhood intelligence, through its links to educational and job attainment, may affect an adult's ultimate access to healthcare, ability to adhere to treatments or exposure to hazardous environments. It may also affect an adult's health literacy, the ability to understand health information and put it into practice.

The findings, Power's team writes, suggest that while childhood cognitive ability showed only modest effects on heart disease risk factors, those effects could make an important difference as far as population-wide heart disease rates.

SOURCE: American Journal of Public Health, January 2010.