Effects of Type 2 Diabetes on Body Heat Storage During Exercise in the Heat

Abstract

Type 2 diabetes (T2DM) is associated with metabolic, cardiovascular, and neurological dysfunctions which may impair thermoregulatory mechanisms during heat exposure escalating the risk of heat-related illnesses and injuries. The risks may be greater where these individuals perform exercise in hot environments, as the ability to maintain core temperature during heat stress becomes compromised. PURPOSE: To examine the effects of diabetes-related decreases in local heat loss responses of skin blood flow (SkBF) and sweating (LSR) on the rates of whole-body evaporative and dry heat loss and change in body heat content (DHb) during and following exercise performed under heat stress. METHODS: Fourteen adults age 45 to 65 years with (n=7) and without (n=7, CON) T2DM (>5 years duration) were matched for age, fitness, body fat, and body surface area/mass ratio. Participants cycled for 60-min at a constant rate of heat production of ∼325 W (∼56% VO2peak) followed by 60-min of recovery in a whole-body direct calorimeter at 24°C (temperate) and 30°C (hot) ambient conditions. Rectal temperature (Tre), LSR and SkBF were measured continuously. RESULTS: After 60-min exercise, average DHb was similar between groups at 24°C (+266±72 kJ and +247±44 kJ for CON and T2DM) and 30°C (+260±72 kJ and +248±30 kJ for CON and T2DM). Similar increases in whole-body heat loss, Tre, LSR and SkBF were also found. No differences in the DHb was measured between groups during the 60-min recovery (24°C: -129±66 kJ and -156±41 kJ; 30°C: -111±48 kJ and -123±38 kJ for CON and T2DM). A net positive DHb remained at end of recovery for both groups under both ambient conditions (p<0.05). This was paralleled by a sustained elevation in Tre in both groups at the 30°C ambient condition only (0.18±0.18°C and 0.21±0.08°C for CON and T2DM; p<0.05). No group differences in whole-body or local (LSR and SkBF) responses were observed. CONCLUSION: Despite previous suggestions of an impaired thermoregulatory response during heat exposure in T2DM, no differences were observed in whole-body heat loss and DHb during exercise performed in temperate or hot ambient conditions relative to matched-controls. Further studies are required to examine these responses under greater levels of thermal stress. Funding support: Natural Sciences and Engineering Research Council of Canada.