Cardiorespiratory fitness in early adulthood significantly decreases the chance of developing hypertension, metabolic syndrome, and diabetes in middle age, according to an article in the December 17th issue of the Journal of the American Medical Association. Furthermore, the researchers found that improving fitness in healthy young adults can decrease risk by as much as 50 percent for diabetes and metabolic syndrome.

The current study is the first, large observational project to look at the role of fitness on healthy young adults' development of risk factors for heart disease. Prior studies had examined the relationship between fitness and mortality from heart disease and stroke.

"This study underscores the importance of both fitness and maintaining a healthy weight in the fight against heart disease and stroke and their risk factors," said Barbara Alving, MD, if the National Institutes of Health. "Americans need to become physically active early in life and continue to be active as they age in order to remain as healthy as possible."

"Given the epidemic of obesity in the United States and the decline in people's physical activity, it's important that Americans take steps to improve their physical fitness," cautioned Mercedes Carnethon, MD, lead author of the study. "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."

The data used in the current study came from the Coronary Artery Risk Development in Young Adults (CARDIA) study, which began in January 1984 and ended in December 2001. The fitness study involved 4,487 black and white American men and women, who were ages 18 to 30 years at baseline. All participants were followed for 15 years, but 2,478 of the total of 4,487 (55.2 percent) had cardiorespiratory fitness tested 7 years post-baseline in order to measure changes in fitness.

Cardiopulmonary fitness was measured with an exercise treadmill test, which included up to 9 2-minute-long stages of progressive difficulty. Women were classified as "low" in fitness if they completed less than 6 minutes of exercise and men if they completed less than 10 minutes. Women who completed 6-9 minutes of exercise were classified as "moderately" fit and men if they completed 10-12 minutes. Those who completed more exercise were classified as "highly" fit.

General trends were the same for both black and white adults, as well as for men and women. People who were low or moderately fit at baseline had twice the risk for hypertension, diabetes, and metabolic syndrome as those who were highly fit. Moreover, risk increased directly as fitness level decreased. Weight gain over the course of follow-up was inversely related to changes in fitness.

Among the 2,478 people who had fitness tested 7 years after baseline, average weight gain at that time was 15 pounds, with an average weight gain of 28 pounds after 15 years. People who were or became obese over the course of the study tended to be less fit: Among obese adults, 68 percent were low in fitness, 29 percent were moderately fit, and 4 percent were highly fit. Of those who were not obese, 13 percent were low in fitness, 36 percent were moderately fit, and 51 percent were highly fit.

It was notable that fitness did not protect people who were highly fit and obese at the start of the study from developing diabetes or metabolic syndrome later in life.

"The key point from this study is that the development of risk factors for heart disease and stroke isn't just the natural result of aging," said Carnethon. "All Americans -- including women and minorities -- can protect themselves against those risks by maintaining their physical fitness.

"Americans don't have to run marathons to improve their physical fitness," said Cheryl Nelson, of the National Institutes of Health. "They should try to engage in at least 30 minutes of a moderate-intensity physical activity such as brisk walking on most and, preferably, all days of the week. Being physically active will not only improve their fitness but also help them maintain a healthy weight, which in turn will protect their heart health."