Relationships between Physical Inactivity and Insulin Secretory Capacity in Non-obese Subjects with Type2 Diabetes Mellitus

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PURPOSE: In western countries, obesity is a major risk factor for developing insulin resistance and the onset of type 2 diabetes mellitus (DMII). Conversely, Japanese adults with DMII are often not obese, but have a genetically low insulin secretory capacity. Current Japanese guidelines for treatment of DMII are mainly based on evidence from studies done with obese subject with DMII. Although exercise plays an important role in improving insulin resistance and reducing the risk of DMII, the effects of exercise in non-obese patients with DMII have not been well-studied. We investigated the association between insulin secretory capacity and daily physical activity and sedentary time in non-obese Japanese adults with DMII. METHODS: Subjects were non-obese adult men with DMII (DM; n=12, age; 54.5±7.2 yr, BMI; 24.0±1.8 kg/m2) and a control group of non-obese healthy adult men (C: n=10, age; 53.9±6.6 yr, and BMI; 24.0±1.7 kg/m2). Daily physical activity and sedentary time were measured using a triaxial accelerometer (HJA-350IT OMRON Corporation). Insulin and glucose were measured prior to and two hours after standard meal ingestion. Fasting C-peptide concentrations and the homeostatic model assessment beta cell function (HOMA-β)were used as indices of insulin secretory capacity. RESULTS: Daily step counts and time spent sedentary and in low, moderate, and vigorous physical were not different between two groups (P > 0.05). HOMA-β in DM was significantly lower than in C (DM; 21.1±9.3 %, C; 48.4±23.2 %). The correlation between HOMA-β and moderate to vigorous intensity physical activity time was not significant in either C (r=-0.20, P=0.61) or DM (r=0.13, P=0.68). However, in DM, there was a significant inverse correlation between sedentary and HOMA-β (r=-0.62, P < 0.03) and C-peptide (r=-0.81, P<0.01). CONCLUSIONS: In non-obese Japanese men with DMII, time spent in sedentary behaviors, but not time spent in physical activity, is associated with reduced insulin secretion. These results suggest that reducing inactivity time may be an appropriate strategy to increase insulin secretion capacity in non-obese patients with DMII.