A Single Sauna Session Does Not Improve Postprandial Blood Glucose Handling in Individuals with Type 2 Diabetes Mellitus: A Cross-Over, Randomized, Controlled Trial.

Introduction: Passive heat treatment has been suggested to improve glycemic control in individuals with type 2 diabetes mellitus (T2DM). Previous studies have focused predominantly on hot water immersion and traditional sauna bathing, as opposed to the more novel method of infrared-based sauna bathing. Here, the impact of a single infrared sauna session on post-prandial glycemic control was assessed in older individuals with T2DM.

Methods: In this randomized controlled crossover trial, 12 participants with T2DM (male/female: 10/2, age: 69±7 y, BMI: 27.5±2.9 kg/m²) rested in an infrared sauna twice: once in a heated (60°C) and once in a thermoneutral (21°C) condition for 40 min, immediately followed by a 2-h oral glucose tolerance test (OGTT). Venous blood samples were obtained to assess plasma glucose and insulin concentrations and to determine the whole-body composite insulin sensitivity index.

Results: Body core and leg skin temperature were higher following the heated condition compared to the thermoneutral condition (38.0±0.3 vs. 36.6±0.2°C and 39.4±0.8 vs. 31.3±0.8°C, respectively; P<0.001 for both). The incremental area under the curve (iAUC) of plasma glucose concentrations during the OGTT was higher after the heated condition compared to the thermoneutral condition (17.7±3.1 vs. 14.8±2.8 mmol/L/120 min; P<0.001). No differences were observed in plasma insulin concentrations (heated: 380±194 vs. thermoneutral: 376±210 pmol/L/120 min; P=0.93) or whole-body composite insulin sensitivity indexes (4.5±2.8 vs. 4.5±2.1; P=0.67).

Conclusions: A single infrared sauna session does not improve postprandial blood glucose handling in individuals with T2DM. Future studies should assess the effect of more prolonged application of infrared sauna bathing on daily glycemic control.