Acute effect of passive heat exposure on markers of cardiometabolic function in adults with type 2 diabetes mellitus

Abstract

Aim: Heat therapy is a promising strategy to improve cardiometabolic health. This study evaluated the acute physiological responses to hot water immersion in adults with type 2 diabetes mellitus (T2DM). Methods: On separate days in randomized order, 13 adults with T2DM (8 males/5 females, 62 ± 12 yrs, BMI: 30.1 ± 4.6 kg/m2) were immersed in thermoneutral (34°C, 90 minutes) or hot (41°C, core temperature ≥38.5°C for 60 minutes) water. Insulin sensitivity was quantified via the minimal oral model during an oral glucose tolerance test (OGTT) performed 60 minutes after immersion. Brachial artery flow-mediated dilation (FMD) and reactive hyperemia were evaluated before and 40 minutes after immersion. Blood samples were drawn to quantify protein concentrations and mRNA levels of HSP70 and 90, and circulating concentrations of cytokines. Results: Relative to thermoneutral water immersion, hot water immersion increased core temperature (+1.66°C [+1.47, +1.87], P<0.01), heart rate (+34 bpm [+24, +44], P<0.01), antegrade shear rate (+96 s-1 [+57, +134], P<0.01), and IL-6 (+1.38 pg/mL [+0.31, +2.45], P=0.01). Hot water immersion did not exert an acute change in insulin sensitivity (-0.3 dl/kg/min/μU/ml [-0.9, +0.2], P=0.18), FMD (-1.0% [-3.6, +1.6], P=0.56), peak (+0.36 mL/min/mmHg [-0.71, +1.43], P=0.64) and total (+0.11 mL/min/mmHg x min [-0.46, +0.68], P=0.87) reactive hyperemia. There was also no change in eHSP70 (P=0.64), iHSP70 (P=0.06), eHSP90 (P=0.80), iHSP90 (P=0.51), IL1-RA (P=0.11), GLP-1 (P=0.59) and NFkB (P=0.56) after hot water immersion. Conclusion: The physiological responses elicited by hot water immersion do not acutely improve markers of cardiometabolic function in adults with T2DM.

The acute effect of heat exposure on forearm macro‐ and microvascular function: Impact of measurement timing, heating modality and biological sex

“…Data are presented as the mean difference (females minus males) with upper 90% confidence interval after forearm heating with an electric blanket (EB, 11 males and seven females), forearm hot water immersion (WI, 11 males and nine females), whole-body heating with the arm covered (WBH-C, 11 males and eight females), whole-body heating with the arm uncovered (WBH-U, 11 males and seven females) and whole-body heating with the arm covered and uncovered when FMD was calculated from end-occlusion diameter (WBH-C* and WBH-U*). The green shading depicts the equivalence limit (3%) et al, 2020; Behzadi et al, 2022;Brunt, Jeckell et al, 2016;Engelland et al, 2020;Gravel et al, 2019). Although it was not the specific objective of this study, the results provide a basis for future studies to perform brachial artery FMD measurements within ∼30-45 min post-heating to study how various factors might modulate the acute effect of heat exposure on macrovascular function.…”

“…It has been hypothesized that the cardiovascular adjustments following acute heat exposure might predict longer‐term adaptations (Romero et al., 2022 ). However, the acute effect of heat exposure on FMD and PORH has proved variable, with some studies observing an improvement in FMD (Cheng et al., 2019 , 2021 ; Coombs et al., 2021 ; Gravel et al., 2020 ; Romero et al., 2017 ; Tinken et al., 2009 ) or PORH (Cheng et al., 2021 ; Romero et al., 2017 ), whereas others did not observe an acute change in FMD (Alali et al., 2020 ; Behzadi et al., 2022 ; Brunt, Jeckell et al., 2016 ; Coombs et al., 2019 ; Engelland et al., 2020 ; Gravel et al., 2019 ; Thomas et al., 2016 ) or PORH (Behzadi et al., 2022 ; Brunt, Jeckell et al., 2016 ; Engelland et al., 2020 ; Gravel et al., 2020 , 2019 ).…”

“…First, previous studies measured vascular function at a single time point following heat exposure, and these time points have ranged from during heating to immediately after heating to ≤60 min post‐heating. Studies in which an acute effect of heating was observed typically involved measurements within 30–45 min post‐heating (Cheng et al., 2019 , 2021 ; Coombs et al., 2021 ; Gravel et al., 2020 ; Romero et al., 2017 ; Tinken et al., 2009 ), whereas no effect was observed when measurements were performed ∼45–60 min post‐heating (Behzadi et al., 2022 ; Brunt, Jeckell et al., 2016 ; Engelland et al., 2020 ; Gravel et al., 2019 ). Given it is unknown whether any acute change in vascular function after heating is transient or long lasting, it is possible that previous studies involving measurements within a longer time frame missed the window to detect an acute change in macro‐ and/or microvascular function.…”

Acute and adaptive cardiovascular and metabolic effects of passive heat therapy or high‐intensity interval training in patients with severe lower‐limb osteoarthritis

“…Another possibility is that passive heat therapy is not effective for improving glycemic control, or may even be deleterious. Acute passive heat exposure results in acute glucose intolerance in non‐diabetic and diabetic individuals (Behzadi et al, 1985 ; Leicht et al, 2019 ; Maley et al, 2019 ), with peripheral tissue glucose uptake reduced in response to hot‐water immersion (but not thermoneutral exposure) (Maley et al, 2023 ). It is plausible the sympathetic response that occurs during hot‐water immersion increases hepatic glucose output; however, the metabolic demands are not sufficient to utilize this additional substrate.…”

Effect of heat therapy compared with strength training on metabolic profile, heat shock response, inflammation, cardiovascular responses and microbiota in individuals with type 2 diabetes: Study protocol of a randomized trial

“…Recently, a cross-sectional study found that habitual hot-tub bathing was associated with slight improvements in HbA1c and body mass index [39]. Acutely, a randomized crossover trial showed that 90 min of hot water immersion did not improve insulin sensitivity, markers of micro-and macrovascular functions, or circulating and intracellular HSP70 concentrations [40]. There is a lack of consistent data in the literature, and, furthermore, the possible mechanisms by which bene ts can be obtained remain unknown.…”