The effect of repeated hot water immersion on insulin sensitivity, heat shock protein 70 and inflammation in individuals with type 2 diabetes mellitus

Objectives: Repeated hot water immersion (HWI) can improve glycaemic control in healthy individuals, but data are limited for individuals with T2DM. The present study investigated whether repeated HWI improves insulin sensitivity, inflammatory status, reduces plasma ([extracellular heat shock protein 70]) [eHSP70] and resting metabolic rate (RMR).

Materials and methods: Fourteen individuals with T2DM participated in this pre- vs. post-intervention study, with outcome measures assessed in fasted (≥ 12 h) and post-prandial (2 hr post-75 g glucose ingestion) states. HWI consisted of 1 h in 40°C water (target rectal temperature 38.5 - 39°C) repeated 8-10 times within a 14-day period. Outcome measures included: insulin sensitivity, plasma [glucose], [insulin], [eHSP70], inflammatory markers, RMR and substrate utilisation.

Results: The HWI intervention increased fasted insulin sensitivity (p = 0.03) and lowered fasted plasma [insulin] (p = 0.04), but fasting plasma [glucose] (p = 0.83), [eHSP70] (p = 0.08), [IL-6] (p = 0.55), [IL-10] (p = 0.59), post-prandial insulin sensitivity (p = 0.19), plasma [glucose] (p = 0.40) and [insulin] (p = 0.47) were not different. RMR reduced (p < 0.05), although carbohydrate (p = 0.43) and fat oxidation (p = 0.99) rates were unchanged.

Conclusion: This study shows that 8-10 HWIs within a 14-day period improved fasting insulin sensitivity and plasma [insulin] in individuals with T2DM, but not when glucose tolerance is challenged. HWI also improves metabolic efficiency (i.e. reduced RMR). Together, these results could be clinically important and have implications for metabolic health outcomes and well-being in individuals with T2DM.