Objectively Measured Moderate- and Vigorous-Intensity Physical Activity but Not Sedentary Time Predicts Insulin Resistance in High-Risk Individuals

OBJECTIVE - Low levels of physical activity appear to be associated with insulin resistance. However, the detailed associations of these complex relationships remain elusive. We examined the prospective associations between self-reported TV viewing time, objectively measured time spent sedentary, at light-intensity activity, and at moderate- and vigorous-intensity physical activity (MVPA) with insulin resistance. RESEARCH DESIGN AND METHODS - In 192 individuals (81 men and 111 women) with a family history of type 2 diabetes, we measured physical activity and anthropometric and metabolic variables at baseline and after 1 year of follow-up in the ProActive UK trial. Physical activity was measured objectively by accelerometry. Insulin resistance was expressed as fasting insulin and the homeostasis model assessment score (HOMA-IR). RESULTS - Baseline MVPA was a significant predictor of fasting insulin at follow-up (beta = -0.004 [95% CI -0.007 to -0.0001], P = 0.022), and the association approached significance for HOMA-IR (beta = -0.003 [-0.007 to 0.000002], P = 0.052), independent of time spent sedentary, at light-intensity activity, sex, age, smoking status, waist circumference, and self-reported TV viewing. Time spent sedentary and at light-intensity activity were not significantly associated with insulin resistance. The change in MVPA between baseline and follow-up was inversely related to fasting insulin (beta = -0.003 [-0.007 to -0.0003], P = 0.032) and the HOMA-IR score (beta = -0.004 [-0.008 to -0.0011, P = 0.015) at follow-up, after adjustment for baseline phenotype in addition to the same confounders as above. CONCLUSIONS - These results highlight the importance of promoting moderate-intensity activity such as brisk walking for improving insulin sensitivity and possibly other metabolic risk factors to prevent type 2 diabetes.