RESUMEN
Context: It is unclear whether immersion in cool water, typical of many beaches, increases the concentration of blood glucose in individuals with type 1 diabetes mellitus (T1DM). Objective: To test the hypothesis in individuals with T1DM that immersion neck-deep in cool water (COOL) causes an increase in blood glucose concentration, but not exposure to thermoneutral water (THERMO) or thermoneutral air. Methods: Eight overnight-fasted participants with T1DM were exposed for 60 minutes on separate days to 3 experimental conditions: cool water (COOL, 23 °C); thermoneutral water (THERMO, 33.5 °C); or thermoneutral air (24 °C). They then recovered for 60 minutes on land at 24 °C. At time intervals, we measured: blood glucose and plasma insulin concentration, rate of carbohydrate and fat oxidation, skin and core temperature, subcutaneous blood flow, and shivering via electromyography. Results: There was no change in blood glucose concentration during the 3 experimental conditions (P > .05). During recovery after COOL, blood glucose increased (P < .05) but did not change in the other 2 conditions. The rate of carbohydrate oxidation during and early after COOL was higher than in the other 2 conditions (P < .05), and COOL led to a decrease in subcutaneous blood flow and the concentration of plasma insulin (P < .05). Conclusion: Cool or thermoneutral neck-deep immersion in water does not cause a change in the concentration of blood glucose in people with T1DM, but on-land recovery from COOL causes an increase in blood glucose that may be due, at least in part, to the accompanying decrease in plasma insulin.
RESUMEN
CONTEXT: Current exercise guidelines for individuals with type 1 diabetes (T1D) do not consider the impact that high altitude may have on blood glucose levels (BGL) during exercise. OBJECTIVE: To investigate the effect of acute hypoxia (simulated high altitude) on BGL and carbohydrate oxidation rates during moderate intensity exercise in individuals with T1D. METHODS: Using a counterbalanced, repeated measures study design, 7 individuals with T1D completed 2 exercise sessions; normoxia and hypoxia (~4200 m simulated altitude). Participants cycled for 60 min on an ergometer at 45% of their sea-level VÌO2peak, and then recovered for 60 min. Before, during, and after exercise, blood samples were taken to measure glucose, lactate, and insulin levels. Respiratory gases were collected to measure carbohydrate oxidation rates. RESULTS: Early during exercise (<30 min), there was no fall in BGL in either condition. After 1 h of exercise and during recovery, BGL were significantly lower under the hypoxic condition compared to both pre-exercise levels (P = 0.008) and the normoxic condition (P = 0.027). Exercise in both conditions resulted in a significant rise in carbohydrate oxidation rates, which returned to baseline levels postexercise. Before, during, and after exercise, carbohydrate oxidation rates were higher under the hypoxic compared with the normoxic condition (P < 0.001). CONCLUSIONS: The greater decline in BGL during and after exercise performed under acute hypoxia suggests that exercise during acute exposure to high altitude may increase the risk of hypoglycemia in individuals with T1D. Future guidelines may have to consider the impact altitude has on exercise-mediated hypoglycemia.
