Exercise at higher elevation linked to larger drop in glucose with type 1 diabetes
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People with type 1 diabetes may experience a greater decline in blood glucose when exercising at high altitudes compared with sea level, according to a study published in the Journal of Clinical Endocrinology & Metabolism.
In a small study of seven adults with type 1 diabetes, participants experienced a significantly lower blood glucose after 1 hour of exercise in conditions emulating an altitude of 4,200 meters compared with conditions representing sea level.
“These findings suggest that exercise performed shortly after exposure to high altitude may increase the risk of exercise-mediated hypoglycemia,” Cory Dugan, AFHEA, BSc, a PhD candidate in nutrition and exercise physiology in the school of human sciences at the University of Western Australia in Crawley, Australia, told Healio. “We ask that future guidelines consider these findings to increase the safety of people with type 1 diabetes when traveling from low- to high-altitude areas like the mountains without any acclimatization.”
Dugan and colleagues conducted a randomized single-blind crossover study, recruiting seven adults with type 1 diabetes and free of respiratory disease from January 2019 to September 2019. Participants completed a familiarization session and two exercise sessions. They performed one exercise session in normoxic conditions typical of sea level and the second in a simulated hypoxic condition with an altitude of 4,200 meters. Participants had anthropometric measurements taken at the familiarization session and underwent a graded exercise test to measure peak rate of oxygen consumption. Prior to each exercise session, the researchers measured blood glucose, with exercise only taking place if blood glucose fell between 6 mmol/L and 11 mmol/L. Both sessions consisted of 60 minutes of exercise on a cycle ergometer at 45% of the peak rate of oxygen consumption at sea level. The partial pressure of oxygen was 160 mm Hg at sea level and 92 mm Hg at the higher altitude. Participants had 60 minutes of recovery after each session. Researchers took blood samples at time intervals before, during and after each session to measure glucose, lactate and insulin and collected respiratory gases to measure hydrate oxidation rates.
Prior to exercise, participants did not have a significantly different blood glucose between normoxic and hypoxic conditions. At 60 minutes of exercise and 60 minutes of recovery, blood glucose declined for those exercising at high altitude, but not for those exercising at sea level conditions.
“The heightened risk of hypoglycemia post-exercise under hypoxia compared [with] normoxia suggests that individuals with type 1 diabetes need to take extra care in monitoring their blood glucose levels when exercising in these conditions,” Dugan said. “Furthermore, the alteration of glucoregulation in conjunction with a multiplicity of other factors — for example, inaccurate blood glucose readings and the freezing of insulin at cold temperatures — creates a unique set of challenges for individuals with type 1 diabetes who wish to participate in high-altitude activities.”
Before exercise, participants exercising at higher altitude had higher carbohydrate oxidation rates compared with sea level (P = .002). During exercise, the oxidation rate increased in both the normoxic (P = .001) and hypoxic (P < .001) exercise conditions. Oxidation rates returned to levels similar to pre-exercise during the recovery period. Fat oxidation rates also increased significantly during the hypoxic (P = .001) and normoxic (P < .001) exercise regimens before returning to pre-exercise levels during recovery.
The researchers wrote that the study’s limitations included a small sample and a lack of isotope tracer techniques or muscle biopsies. Dugan said future studies can further investigate the mechanisms causing glucose levels to fall during exercise at higher altitude.
For more information:
Corey Dugan, AFHEA, BSc, can be reached at cory.dugan@research.uwa.edu.au.
Perspective
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Inspirational individuals living with type 1 diabetes have proven their capability to exercise at high altitudes by trekking the highest peaks in the world. While precautions are advised for people exercising at high altitude, including a pre-trek health screen for diabetes-related complications, packing extra diabetes-related supplies and vigilant blood glucose monitoring, few guidelines are set out for insulin dose changes or nutrient requirements.
In a carefully controlled study, Dugan and colleagues examined the influence of simulated high-altitude exercise on blood glucose levels and energy substrate metabolism in young adult men and women living with type 1 diabetes. The researchers simulated sea level (0 meters) and high-altitude conditions (about 4,200 meters) by changing the partial pressure of oxygen in the inspired air from 21% oxygen to 12.1% oxygen, while volunteers with type 1 diabetes cycled on a stationary bike for 60 minutes in an environmental chamber.
When compared to sea level conditions, exercising at the simulated high-altitude condition increased the rate of carbohydrate oxidation and lactate production and caused a greater reduction in blood glucose level both during the exercise and in recovery. As expected, heart rate, ventilation rate and perceived effort were also higher in the high-altitude condition.
The authors concluded that exercise at high altitude causes a greater reliance on carbohydrate as fuel and a greater risk for exercise-associated hypoglycemia in people with type 1 diabetes. This novel work informs diabetes care providers and people with diabetes that exercise at high altitude should be performed with greater precautions for the prevention of hypoglycemia, such as insulin reductions or increased carbohydrate ingestion during and after exercise.
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