This is the longest observational study to focus on the relationship between aerobic fitness and the development of diabetes. Most previous research has focused on the self-reported health behavior of physical activity, but people don't always accurately report their activity level. Fitness, easily measured by a standard treadmill test, provides a more accurate measure than a self-report.

In addition, this study is the first to look at the development of diabetes over a 20- year period. Because diabetes develops over a long period of time, the number of people affected in the population rises with age. Previous studies that followed adults for a shorter period of time may have stopped short before diabetes was diagnosed.

Data from the 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 included 3,989 participants at baseline and 2,231 at the 20-year testing. The black and white men and women were 18 to 30 at the time of enrollment. Fasting blood sugar levels (the blood marker used to define diabetes) were measured at the beginning of the study and multiple times over 20 years.

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