Young adults who are unfit are three to six times more likely to develop diabetes, high blood pressure and other ailments in middle age that put them at greater risk of heart disease or stroke, according to a new study.

The study in the Journal of the American Medical Association found that increasing fitness decreased the risk by as much as 50 per cent.

The study was published in the Journal’s December 17 issue.

“If all the young adults in our study had been fit, there would have been nearly a third fewer cases of high blood pressure, diabetes and metabolic syndrome,” said Mercedes Carnethon of Northwestern University, lead author of the study.

“Given the epidemic of obesity in the United States and the decline in people’s physical activity, its important that Americans take steps to improve their physical fitness.”

Heart disease and stroke are the first and third leading causes of death for Americans.

According to the National Heart, Lung and Blood Institute, nearly 13 million Americans have heart disease and nearly five million have had a stroke.

The study is the first major one to research how the role fitness plays in the development of coronary risk factors in healthy young adults.

Researchers tracked more than 4,400 men and women between the ages of 18 to 30 for 15 years, but about 2,500 had their cardiopulmonary fitness retested after sevenyears to measure changes in fitness.

Fitness was measured with an exercise treadmill test