Relationship Between Habitual Physical Activity and Insulin Levels Among Nondiabetic Men and Women: San Luis Valley Diabetes Study

OBJECTIVE: To determine whether higher levels of physical activity would be associated with lower fasting insulin and C-peptide levels in a free-living nondiabetic population. RESEARCH DESIGN AND METHODS: A cross-sectional study was conducted with a Hispanic and non-Hispanic white population of 442 men and 489 women with normal glucose tolerance (by World Health Organization criteria) in two rural Colorado counties. Total physical activity was assessed by a 7-day physical activity recall from which metabolic equivalents were estimated. Relationships between metabolic equivalents and fasting insulin and C-peptide were assessed while considering obesity, age, and other risk factors known to influence fasting insulin levels. RESULTS: Among all subjects, univariate analyses showed that higher activity levels were associated with lower mean fasting insulin and C-peptide levels (P less than or equal to 0.05). Multiple linear regression showed that higher activity was significantly associated with lower values of log fasting insulin and C-peptide levels in men only (P less than 0.001) independent of obesity, fat distribution, and age. Men in the highest tertile of activity had an adjusted mean fasting insulin level of 59.2 pM and fasting C-peptide level of 0.5 nM compared with a fasting insulin level of 72.7 pM and fasting C-peptide level of 0.6 mM for men in the lowest tertile of activity. The magnitude of the inverse association between activity and insulin was greatest in older rather than younger men. Physical activity was not associated with fasting insulin or C-peptide levels in women in the multivariate analyses. CONCLUSIONS: Based on cross-sectional data, we conclude that higher levels of habitual physical activity are associated with lower fasting insulin and C-peptide levels in Hispanic and non-Hispanic white men.