The combined effect of high-intensity intermittent training and vitamin D supplementation on glycemic control in overweight and obese adults

High-intensity intermittent training (HIIT) has been shown to reduce the risk of chronic conditions including the development of type 2 diabetes mellitus (T2DM). Independently, a low vitamin D status has also been linked to the prevalence of T2DM. The aim of this study was to investigate if there was a synergistic metabolic effect of HIIT and vitamin D supplementation on glycemic control. A total of 20 male and female participants (age, 34 ± 9 year; BMI, 31.4 ± 2.8 kg·m ⁻² ) completed 6 weeks HIIT, and were randomized to ingest 100 μg·day ^-1 of vitamin D ₃ or placebo. Response to an oral glucose tolerance test (OGTT) was determined at baseline and at 72 h postintervention. Glucose tolerance was improved as a result of the HIIT intervention, shown through a reduction in glucose and insulin concentrations during the OGTT, accompanied by a decrease in glucose (829 ± 110 to 786 ± 139 mmol·h ⁻¹ ·L ⁻¹ ; P = 0.043) and insulin (8101 ± 4755–7024 ± 4489 mU·h ⁻¹ ·L ⁻¹ ; P = 0.049) area under the curve (AUC). Supplementation increased 25-hydroxyvitamin D ₃ concentration by 120% to a sufficiency status (P < 0.001). However, the consumption of vitamin D ₃ seemed to attenuate the glucose response during an OGTT. Triglyceride content was lowered following the intervention (P = 0.025). There was no effect of the intervention on insulin sensitivity (IS) indices: ISI _{M atsuda} and HOMA-IR. Our findings demonstrate that HIIT improves glucose tolerance in nondiabetic overweight and obese adults; however vitamin D ₃ supplementation did not proffer any additional positive effects on the measured indices of metabolic health.