Researchers have for years believed that fat, unfit adults are more likely to have high blood pressure, a measure of heart-disease risk. But now it appears that children as young as 5 who are fat and unfit also may be at risk.

According to a new study of inner-city 5- and 6-year-olds, the fatter and less aerobically fit a young child is, the more likely he or she is to have high blood pressure.

The study, reported in today's Journal of the American Medical Association, found that children's blood pressure increased as their fitness decreased. Children who were fat and who had to work harder to keep up a certain pace on a treadmill were more likely to have high blood pressure.

"Cardiovascular disease is thought of as an adult problem," said Bernard Gutin, the report's lead author. "What we're seeing now is even as young as 5 or 6, one of the key factors for heart disease is related to how fit or fat they are."

Gutin said his study is the first to find an association between fitness and high blood pressure in children as young as 5. Previous studies had found such an association in older children, he said.

One rationale for promoting fitness among children has been that people who learn healthy habits early in life are more likely to practice them as adults. But the study's authors said that while that may be true, obesity and lack of exercise may also have an impact that begins in childhood.

The findings say nothing about whether the children with high blood pressure are more likely to develop heart disease as they grow older. But earlier studies that followed young children for 10 to 15 years found that those with higher blood pressure who later died in accidents were more likely to show lesions in the blood vessels supplying their hearts than were children who had had lower blood pressure and later died in accidents. Such evidence indicates that high blood pressure may cause heart disease in the young as well as in the old, Gutin said.

"There's an implication {from those studies} that high blood pressure even at age 5 or 6 may be causing damage to the arteries," Gutin said.

The study looked at 216 children in New York, most of whom were Hispanic. Researchers judged fitness by measuring how hard the children had to work on a treadmill and determined fatness by using calipers to measure skin folds and by calculating their body mass index, which is a measure of weight proportionate to height. A statistical analysis of those measurements indicated that as fitness decreased and fatness increased, blood pressure rose.

Gutin said he and his colleagues chose inner-city children for their study because they are more likely to be less physically active and overweight.

"The problem of fatness in children, and probably also of reduced physical activity, is most evident in inner-city populations," he said. "The solution for this problem is to figure out a way to make children more physically active so they can still eat a healthy amount of food but not get fat."

Michael J. Horan, a hypertension specialist at the National Heart, Lung and Blood Institute, said the findings did not surprise him. "It's concordant with what we know about adults," he said. "It's a piece of evidence in support of the notion that cardiovascular risk is related to lifestyle."