Exercise immediately after insulin dosing ‘unsafe’: Pilot study
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A low insulin level coupled with euglycemia or modest hyperglycemia are the most favorable conditions for exercise for people with type 1 diabetes, findings from a small pilot study suggest.
“It is unsafe to exercise shortly after taking a dose of insulin,” Rita Basu, MD, professor of medicine in the division of endocrinology and clinical education director of the Center for Diabetes Technology at the University of Virginia School of Medicine, told Healio. “Moderate exercise in people with type 1 diabetes to maintain active lifestyle is preferred when their blood glucose levels are normal or modestly elevated, but not when their circulating insulin concentrations are raised, such as shortly after a bolus or prandial dose of insulin.”
Basu and colleagues analyzed data from six participants without diabetes (two women) and six participants with type 1 diabetes (three women; mean diabetes duration, 16 years; all using insulin pump therapy), matched for age, fat-free mass measured via DXA, and VO2 max levels determined via exercise test. Participants reported for three visits in the morning after an overnight fast for one of three tests using glucose infusion, conducted in random order: euglycemia, low insulin; euglycemia, high insulin; and hyperglycemia, low insulin. Glucose fluxes were measured using [6,6-2H2]glucose before, during and after 60 minutes of exercise.
Researchers found that the rate of glucose disappearance increased with exercise within groups (P < .01). However, peak rate of glucose disappearance during exercise was lower among participants with type 1 diabetes (P < .01) vs. participants without diabetes (P < .01) during all visits.
Among participants with type 1 diabetes, endogenous glucose production increased with exercise during the euglycemic, low-insulin and hyperglycemic, low-insulin visits, but not during the euglycemic, high-insulin visit.
“This demonstrates that hyperinsulinemia, but not hyperglycemia, blunts the compensatory exercise-induced increase in endogenous glucose production in type 1 diabetes,” the researchers wrote.
Basu said understanding the physiologic mechanisms of exercise in type 1 diabetes is still an unmet need.
“Regular exercise and physical activity are required to maintain a healthy lifestyle; however, many people with type 1 diabetes are fearful of hypoglycemia and/or hyperglycemia and are unable to maintain adequate glucose levels before, during and after exercise,” Basu said. “This requires further study.”
For more information:
Rita Basu, MD, can be reached at the Division of Endocrinology, University of Virginia School of Medicine, 560 Ray C Hunt Drive, Room 3108, Charlottesville, VA 22908; email: basu.rita@virginia.edu.
Perspective
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Sheri R. Colberg, PhD, FACSM
This pilot study by Romeres and colleagues addresses an important consideration for anyone with type 1 diabetes: how to exercise with as close to a normal metabolic response as possible.
Given that insulin in their case must be delivered peripherally and not directly to the portal circulation via the pancreas, insulin levels in peripheral areas during exercise are often higher than normal and may impact muscle uptake. Meanwhile, the insulin-to-glucagon balance at the level of the liver may not be normal, and glucose turnover is impaired as a result.
It is not surprising that the study found that hyperinsulinemia, but not hyperglycemia, blunts the compensatory exercise-induced increase in endogenous glucose production, since such high levels of peripheral insulin likely translate to higher portal levels that blunt glucose release by the liver. Prior studies in type 2 diabetes have also shown that hyperglycemia likely increases blood glucose uptake by active muscles, likely due to a mass action effect, and this study suggests that similar mechanisms are in play during exercise in type 1 diabetes.
While the findings of this study are important, the study itself is somewhat limited by the fact that there is no way to know if the exercise intensity performed by participants with diabetes was similar to that of the control group. The researchers defined moderate activity as 65% of VO2 max rather than using the more widely accepted VO2R, defined as a reserve, or a percentage of the difference between resting oxygen consumption and maximal, added back to the resting value, which would have allowed for more accurate modulation of intensities between individuals. The peak rate of glucose disappearance during exercise that was found to be lower among participants with type 1 diabetes may have been the result of differences in VO2 max between groups, but there is no way to discern this due to their methodology.
Nonetheless, this pilot study presents novel and important findings that may make it easier for people with type 1 diabetes to effectively maintain euglycemia during aerobic exercise. Clearly, more research to confirm these findings and to study the impact of other intensities and types of activities is recommended to enhance our understanding.
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