50-80% basal rate reduction lowers the risk of exercise-induced hypoglycemia.
During physical activities, a reduction in insulin secretion and an increase in glucagon secretion occurs to increase the amount of glucose production by the liver. Therefore, the glucose production becomes equal to glucose utilization during exercise in healthy individuals. Patients with diabetes, particularly patients with type 1 diabetes, are not able to produce insulin due to destruction of pancreatic beta cells. These patients require insulin therapy to control their serum glucose. Exogenous insulin is usually administered via continued insulin infusion therapy (CII) or multiple injection, to mimic endogenous insulin.
Exogenous insulin comes in both long-acting, normally used as basal insulin, and rapid or short acting, used as bolus or meal time insulin. Short-acting insulin is the only type of insulin used with CSII therapy, both basal and bolus insulin. During aerobic exercises, in patients with type 1 diabetes, the insulin level seems to stay elevated, although the insulin infusion is suspended. Therefore, the risk of hypoglycemia is higher in patients with type 1 diabetes since exogenous insulin levels are increased.
One of the ways to reduce the risk of hypoglycemia for an active patient with type 1 diabetes is to intake higher amounts of carbohydrates before exercise. Additionally, decreasing the mealtime insulin dose and performing a basal rate reduction before starting to exercise may be helpful. While there is not enough evidence to back up this recommendation, it is suggested to perform a basal rate reduction about 60 to 90 minutes before onset of exercise.
A study conducted by DirecNet study group assessed the effect of discontinuing basal insulin regarding frequency of hypoglycemia during exercise in children with type 1 diabetes. Results of this study revealed that in 49 pediatric patients with type 1 diabetes, exercise induced hypoglycemia, which was defined as serum glucose ≤70 mg/dL, happened less often when the basal insulin was discontinued than when it was continued (16% vs. 43%; P=0.003). Therefore, stopping basal insulin at the start of a 75-min aerobic exercise may decrease exercise induced hypoglycemia but not eliminate the risk.
A recently published study was conducted to determine what type of basal rate reduction would be superior in reducing the occurrence of hypoglycemic episodes during prolonged aerobic exercise in patients with type 1 diabetes using CSII. Researchers assessed the change in blood glucose during the time of exercise and 2 hours after a standardized meal post exercise. This study is referred to as the Omnipod Type 1 diabetes Insulin Management for Exercise (OmniTIME) Study.
Inclusion criteria consisted the following: ages of 17–65 years, minimum of 1-year diagnosis of diabetes, minimum of using CSII therapy for 1 month (total daily dose of at least 0.25 units/kg); and HbA1c level of 9.9%. Any patient who had history of recurrent and erratic hypoglycemia and was not able to exercise regularly due to an injury or health conditions was excluded from this study. In the OmniTIME Study, seventeen patients with type 1 diabetes completed three sets of 60-min treadmill exercise with average 50% of VO2peak. Moreover, insulin strategies in the study were as follows :1) discontinuation of pump at the start of exercise, 2) a basal rate reduction of 80%, 90 minutes prior to exercise, and 3) a basal rate reduction of 50%, 90 minutes prior to exercise. By using two-way repeated-measures ANOVA, researchers compared the changes in blood glucose concentration, carbohydrate and fat oxidation rates, and respiratory exchange ratio from the first to the last session of exercise.
Results from the data analysis showed that, with a 50% higher blood glucose level at the start of exercise with 50% basal rate reduction (191 ±49 mg/dL) in comparison to 80% basal rate reduction (164±41 mg/dL; P< 0.001), a total of 7 out of 17 participants developed hypoglycemia, with discontinuation of pump at the start of exercise. In contrast, only 1 out of 17 participants developed hypoglycemia with both 50% and 80% basal rate reductions (P< 0.05); an increase in blood glucose concentration was noted following a standardized meal post exercise, with discontinuation of pump and with 50% basal rate reduction (both P < 0.05). However, 80% basal rate reduction failed to raise blood glucose concentration (P = 0.16). Lastly, the average percent of time overnight with normal glycemic levels were 83%, 83%, and 78%, and time in hypoglycemia was 2%, 1%, and 5% for 80% basal rate reduction, 50% basal rate reduction, and pump suspension, respectively, based on interstitial glucose (all P >.05). Researchers concluded that overall, a 50–80% basal rate reduction at 90 minutes prior to exercise, may lead to improvement in glucose control and reduction of hypoglycemia risk during exercise, in comparison to discontinuation of pump.
- To reduce exercise-associated hypoglycemia, individuals with type 1 diabetes on continuous subcutaneous insulin infusion typically perform basal rate reductions (BRRs) and/or carbohydrate feeding.
- A 50–80% basal rate reduction at 90 minutes prior to exercise, may lead to improvement in glucose control and reduction of hypoglycemia risk during exercise.
- Only 1 out of 17 participants developed hypoglycemia with both 50% and 80% basal rate reductions (P< 0.05).
Diabetes Research in Children Network (DirecNet) Study Group et al. “Prevention of hypoglycemia during exercise in children with type 1 diabetes by suspending basal insulin.” Diabetes care vol. 29,10 (2006): 2200-4. doi:10.2337/dc06-0495
Zaharieva DP, McGaugh S, Pooni R, Vienneau T, Ly T, Riddell MC. Improved open-loop glucose control with basal insulin reduction 90 minutes before aerobic exercise in patients with type 1 diabetes on continuous subcutaneous insulin infusion [published online February 22, 2019]. Diabetes Care. doi:10.2337/dc18-2204
Ghazal Blair, Pharm.D. Candidate 2019, LECOM School of Pharmacy