The Effects of Passive Heating on Metabolic and Cardiovascular Function in Individuals with Type 2 Diabetes Mellitus

Student thesis: Doctoral Thesis


Type 2 diabetes mellitus (T2DM) is characterised by chronic hyperglycaemia and progressive insulin resistance, leading to macro and microvascular dysfunction and an increased mortality risk. Current treatments for T2DM focus on improving insulin sensitivity and improving glycaemic control. Treatments include physical activity, calorie restriction and hypoglycaemic agents. Although these treatments are generally effective they are not suitable for all individuals. An intervention with therapeutic potential is passive heating (PH) but it has yet to be explored in individuals with T2DM. It was hypothesised that both an acute bout and repeated bouts of PH using hot water immersion (HWI) would improve glycaemic control, insulin sensitivity, inflammation and blood pressure, and that repeated HWI would also improve vascular and central haemodynamic function in individuals with T2DM.
PH was administered by immersing participants initially up to the clavicle using either a hot tub or hot water in a swimming flume at 40 °C in a thermoneutral room, ambient temperature 23 °C (50% relative humidity) for 1 h. Rectal temperature was attained and then clamped between 38.5 and 39 °C by adjusting body position in the water. This was repeated 8-10 times in a 14 day period for chronic passive heating.
The findings from this thesis showed that acute HWI did not improve glycaemic control in individuals with T2DM but it did reduce diastolic blood pressure. Additionally, acute HWI increased eHSP70, heart rate (HR) and total energy expenditure, similar to that of light- intensity exercise, meaning that there may indeed be beneficial adaptation if HWI were conducted repeatedly. Repeated HWI improved fasting insulin sensitivity and lowed plasma [insulin] in individuals with T2DM. It also found that repeated HWI improved cardiometabolic efficiency by simultaneously reducing cardiac output and resting metabolic rate.
In conclusion, this thesis has provided evidence that PH may have therapeutic potential on metabolic and vascular health in individuals with T2DM. There is now a strong rational for future studies to conduct larger, longer, multisite, randomised control trials in this area to provide conclusive evidence for the use of PH as a treatment in T2DM.
Date of Award21 May 2024
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorAnt Shepherd (Supervisor), Jo Corbett (Supervisor) & Zoe Saynor (Supervisor)

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