Effects of Simulated High Altitude on Blood Glucose Levels During Exercise in Individuals With Type 1 Diabetes

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 (similar to 4200 m simulated altitude). Participants cycled for 60 min on an ergometer at 45% of their sea-level (V)over dotO(2peak), 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.