Physical activity has been advocated as an important factor in the primary prevention of non-insulin-dependent diabetes mellitus (NIDDM), but information concerning the specific intensities and durations that are protective has been unavailable. To examine prospectively the association between self-reported levels of the intensity and duration of physical activities, and cardiorespiratory fitness (assessed by respiratory gas exchange) and incident cases of NIDDM (assessed by the oral glucose tolerance test) in a population-based sample of 897 middle-aged Finnish men. After adjustment for age, baseline glucose values, body mass index, serum triglyceride levels, parental history of diabetes, and alcohol consumption, moderately intense physical activities (> or = 5.5 metabolic units) that were undertaken for at least a 40-minute duration per week were associated with a reduced risk of NIDDM (odds ration [OR], 0.44; 95% confidence interval [CI], 0.22-0.88). Activities with less than an intensity of 5.5 metabolic units, regardless of their duration, were not protective. Cardiorespiratory fitness levels greater than 31.0 mL of oxygen per kilogram per minute were protective against NIDDM (OR, 0.26; 95% CI, 0.08-0.82). A subgroup of men at high risk of NIDDM, because they were overweight and were hypertensive and had a positive parental history of NIDDM, who engaged in moderately intense physical activities above the 40-min/wk duration reduced their risk of NIDDM by 64% compared with men who did not participate in such activities. After adjustment for age, baseline glucose levels, and known risk factors, physical activities with an intensity of 5.5 metabolic units or greater and a duration of 40 minutes or greater per week protected against the development of NIDDM. These protective effects were even more pronounced in a subgroup of men who were at high risk for the development of the disease.
