The effect of repeated hot water immersion on insulin sensitivity, heat shock protein 70, and inflammation in individuals with type 2 diabetes mellitus.
Level 4 - case-series / case-control
Uncontrolled pre-post intervention study without a separate control group
PubMed 37938179 · doi:10.1152/ajpendo.00222.2023
What was done
Fourteen individuals with type 2 diabetes mellitus participated in an uncontrolled pre- versus post-intervention study. The intervention consisted of 8 to 10 sessions of hot water immersion (1 hour in 40°C water, targeting a rectal temperature of 38.5°C–39°C) completed over a 14-day period. Outcome measures evaluated in fasted (≥12 h) and postprandial (2 h post-75 g glucose ingestion) states included insulin sensitivity (via QUICKI), plasma glucose, plasma insulin, extracellular heat shock protein 70 (eHSP70), inflammatory markers (IL-6, IL-10), resting metabolic rate (RMR), and substrate utilization.
What was found
Hot water immersion increased fasted insulin sensitivity (QUICKI; P = 0.03) and lowered fasted plasma insulin (P = 0.04). Resting metabolic rate decreased by 6.63% (P < 0.05). No statistically significant differences were observed in fasting plasma glucose (P = 0.83), postprandial insulin sensitivity (P = 0.19), postprandial plasma glucose (P = 0.40), postprandial plasma insulin (P = 0.47), eHSP70 (P = 0.08), IL-6 (P = 0.55), IL-10 (P = 0.59), carbohydrate oxidation (P = 0.43), or fat oxidation (P = 0.99).
Why it matters
This study shows that short-term passive heating can modestly improve fasting insulin sensitivity and reduce resting energy expenditure in type 2 diabetes. However, the absence of effect on challenged postprandial glucose handling indicates limited impact on whole-body glycemic control.
Limits
The study had a very small sample size (n = 14) and lacked a non-heating control group. Absolute values, confidence intervals, and baseline demographics are not reported in the abstract, and the 14-day duration leaves long-term durability and safety unknown.
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