Acute and chronic effects of hot water immersion on inflammation and metabolism in sedentary, overweight adults

Abstract

Regular exercise-induced acute inflammatory responses are suggested to improve the inflammatory profile and insulin sensitivity. As body temperature elevations partly mediate this response, passive heating might be a viable tool to improve the inflammatory profile. This study investigated the acute and chronic effects of hot water immersion on inflammatory and metabolic markers. Ten sedentary, overweight men [body mass index (BMI): 31.0 ± 4.2 kg/m2, mean ± SD] were immersed in water set at 39°C for 1 h (HWI) or rested for 1 h at ambient temperature (AMB). Venous blood was obtained before the session, immediately postsession, and 2 h postsession for assessment of monocyte intracellular heat shock protein-72 (iHsp72) and plasma concentrations of extracellular Hsp72 (eHsp72), interleukin-6 (IL-6), fasting glucose, insulin, and nitrite. Thereafter, participants underwent a 2-wk intervention period, consisting of 10 hot water immersion sessions (INT). Eight BMI-matched participants (BMI: 30.0 ± 2.5 kg/m2) were included as control (CON). Plasma IL-6 and nitrite concentrations were higher immediately following HWI compared with AMB (IL-6 P < 0.001, HWI: 1.37 ± 0.94 to 2.51 ± 1.49 pg/ml; nitrite P = 0.04, HWI: 271 ± 52 to 391 ± 72 nM), whereas iHsp72 expression was unchanged ( P = 0.57). In contrast to resting iHsp72 expression ( P = 0.59), fasting glucose ( P = 0.04; INT: 4.44 ± 0.93 to 3.98 ± 0.98 mmol/l), insulin ( P = 0.04; INT: 68.1 ± 44.6 to 55.0 ± 29.9 pmol/l), and eHsp72 ( P = 0.03; INT: 17 ± 41% reduction) concentrations were lowered after INT compared with CON. HWI induced an acute inflammatory response and increased nitric oxide bioavailability. The reductions in fasting glucose and insulin concentrations following the chronic intervention suggest that hot water immersion may serve as a tool to improve glucose metabolism. NEW & NOTEWORTHY A single hot water immersion (HWI) session induces an acute increase in plasma interleukin-6 and nitrite concentrations but does not acutely elevate heat shock protein-72 expression in monocytes [intracellular Hsp72 (iHsp72)]. A chronic HWI intervention reduces fasting glucose and insulin concentrations in the absence of changes in resting iHsp72. Therefore, HWI shows potential as a strategy to combat chronic low-grade inflammation and improve glucose metabolism in individuals without the physical capacity to do so using exercise.

Hot water immersion acutely increases postprandial glucose concentrations

“…This is a noteworthy finding, as an increased GLP-1 response to an OGTT is predictive of chronic reductions in fasting glucose (Koopman et al 2005). The present results hence imply that the chronic reductions in blood glucose following HWI therapy (Hooper 1999;Hoekstra et al 2018) are not the result of any acute HWI-induced changes to the acute GLP-1 response. The only differential gut hormone response was observed directly following HWI, when the increase in acylated ghrelin concentration was blunted when compared with CON.…”

“…These chronic effects of HWI are similar to responses observed following exercise training (Kränkel et al ). HWI therapy has hence been suggested to represent a potential strategy to improve metabolic health for those unable to exercise (Hoekstra et al ), much like exercise training has been advocated to be a suitable strategy to treat and prevent diseases associated with impaired glycemic control, such as Type II Diabetes (American Diabetes Association ).…”

“…Passively increasing body temperature, by using hot water immersion (HWI) (Brunt et al 2016;Hoekstra et al 2018) or sauna bathing (Imamura et al 2001;Biro et al 2003;Laukkanen et al 2015), can reduce risk markers related to inflammation and cardiovascular health. Moreover, HWI can lower the traditional blood-derived markers associated with Type II Diabetes, such as fasting concentrations of glucose, insulin, or glycosylated hemoglobin after as little as 2 to 3 weeks (Hooper 1999;Hoekstra et al 2018). Chronic HWI interventions further show improvements in glucose tolerance in rats being fed a high-fat diet (Gupte et al 2009), and a normalization of glucose excursions in Vervet monkeys (Kavanagh et al 2016).…”

Could Heat Therapy Be an Effective Treatment for Alzheimer’s and Parkinson’s Diseases? A Narrative Review

“…In human whole-body passive heating models, such as hot water immersion of >60 min whereby core body temperature is increased, higher extracellular HSP70 concentration (Faulkner et al, 2017), and intracellular HSP70 changes (Oehler et al, 2001), have been reported. The beneficial response once again is not unanimous, with others reporting chronic change (following 2 weeks of repeated therapy) in intracellular HSP70 after 45-60 min of passive heat therapy (Hoekstra et al, 2018). In a similar manner to that described for local heating, the dose of stress may be important given the lack of change in studies using 60 min heating (Hoekstra et al, 2018), in comparison to those who do report an acute increase in intracellular HSP70 following 120 min heating in 39 • C water (Oehler et al, 2001).…”

Modality-specific training adaptations – do they lead to a dampened acute inflammatory response to exercise?

“…response, suggesting that the elevation of plasma IL-6 concentrations following exercise are indeed influenced by more than contraction related processes only. As hyperthermia alone can induce elevations in plasma IL-6 concentrations (Hoekstra et al 2018), the elevated circulating IL-6 concentration following the exercise bouts may therefore have also originated from other sites than the exercising muscle groups.…”