Timing of acute passive heating on glucose tolerance and blood pressure in people with type 2 diabetes: a randomized, balanced crossover, control trial

Abstract

Type 2 diabetes mellitus (T2DM) is characterized by chronic hyperglycemia and progressive insulin resistance, leading to macro and microvascular dysfunction. Passive heating has potential to improve glucose homeostasis and act as an exercise mimetic. We assessed the effect of acute passive heating before or during an oral glucose tolerance test (OGTT) in people with T2DM. Twelve people with T2DM were randomly assigned to 3 conditions:1) 3 h OGTT (CON); 2) 1 h passive heating (40 °C water) 30 min before an OGTT (HOT-OGTT); and 3) 1 h passive heating (40 °C water) 30 min after commencing an OGTT (OGTT-HOT). Blood [glucose], insulin sensitivity, extracellular heat shock protein 70 (eHSP70), total energy expenditure (TEE), heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP) were recorded. Passive heating did not alter blood [glucose] (CON, 1,677 (386) a.u.; HOT-OGTT, 1,797 (340) a.u.; OGTT-HOT, 1,662 (364) a.u.; P = 0.28), insulin sensitivity (P = 0.15), or SBP (P = 0.18), but did increase [eHSP70] in both heating conditions (CON, 203.48 (110.81) pg·mL-1; HOT-OGTT, 402.47 (79.02) pg·mL-1; OGTT-HOT, 310.00 (60.53) pg·mL-1; P < 0.001), increased TEE (via fat oxidation) in the OGTT-HOT condition (CON, 263 (33) kcal; HOT-OGTT, 278 (40) kcal; OGTT-HOT, 304 (38) kcal; P = 0.001), increased HR in both heating conditions (P < 0.001) and reduced DBP in OGTT-HOT condition (P < 0.01). Passive heating in close proximity to a glucose challenge does not alter glucose tolerance but does increase [eHSP70] and TEE, and reduce blood pressure in people with T2DM.

The effect of age and mitigation strategies during hot water immersion on orthostatic intolerance and thermal stress

“…However, several studies suggest that this method of heating can be uncomfortable and difficult to tolerate (Hoekstra et al., 2018 ; Zurawlew et al., 2016 ). Furthermore, prolonged hot water immersion can result in negative symptoms, including dizziness, syncope, nausea, headaches and vomiting (Horvath & Botelho, 1949 ; James et al., 2021 ; Menzies et al., 2022 ). In some circumstances, the deleterious effects of heating can also contribute to transient declines in postural control (Mtibaa et al., 2018 ) and cognitive function (Malcolm et al., 2018 ; Sun et al., 2012 ), with previous research linking these factors to the risk of falls in older adults (Johansson et al., 2017 ).…”

“…Although some of these adverse symptoms have been recognized for a long time (Horvath & Botelho, 1949 ), many of the more recent studies investigating hot water immersion appear to overlook these important safety considerations. Indeed, adverse events and safety concerns often receive only a single passing comment in many papers (Hooper, 1999 ; James et al., 2021 ; Zurawlew et al., 2016 ).…”

Exercise Mimetics: An Emerging and Controversial Topic in Sport and Exercise Physiology

“…Acute passive heating has demonstrated some exercise mimetic properties in humans, namely type II diabetics, when implemented in proximity to an oral glucose tolerance test (OGTT) [60]. One-hour of passive heating in water at 40°C either 30 min before or 30 min after commencing an OGTT increased extracellular heat shock protein 70 in the blood and increased heart rate and total energy expenditure (via increased fat oxidation) [60]. However, passive heating did not affect blood glucose concentrations or insulin sensitivity compared with a control group.…”

Hot water immersion as a potential substitute for strength training during the COVID-19 pandemic

“…It also needs to be mentioned that the risk of transient symptomatic hypotension associated with the 40°C water immersion treatment ( Naumann et al, 2017 ) also applies to our protocol. Therefore, the potential users of our treatment should not hurry to stand after completing it and should sit for a few minutes after getting out of the bath to allow blood pressure to return to normal and avoid the potential risk of falling due to syncope ( James et al, 2021 ).…”