Is there a better time to reduce basal insulin before exercise to prevent hypoglycemia?

The aim of this study was to compare three different times to decrease basal insulin to reduce hypoglycemia after exercise in patients with type 1 diabetes. The main finding of the study was that reducing basal insulin by 80% up to 40 minutes before exercise still did not reduce exercise-induced hypoglycemia.

Insulin is the treatment for type 1 diabetes (T1D). It is a hormone that lowers blood glucose. Insulin treatment is made up of basal insulin, which controls blood glucose between meals and also meal-time insulin, which controls blood glucose after meals.

Exercise is an important part of T1D treatment as it lowers risk of heart disease and improves overall wellbeing. However, during exercise, the body uses more glucose. Therefore, exercise decreases the amount of basal insulin needed.

Hypoglycemia is a complication of insulin treatment. It happens when blood glucose goes dangerously low (less than 4 mmol/L). Hypoglycemia can happen after all of the glucose is used up during exercise (exercise-induced hypoglycemia). The best time before exercise to reduce basal insulin to prevent exercise-induced hypoglycemia is still not known.

This study included 22 patients with T1D. Patients were randomized to reduce their basal insulin by 80% at either 40 minutes before exercise (T40), 20 minutes before exercise (T20) or at the time they started to exercise (T0). Patients were treated for 16 months.

There was a lower percentage of time spent with blood glucose levels below 4 mmol/L (hypoglycemia) in patients in the T40 group (16%) compared to T20 (26%) and T0 (24%) groups. This was not statistically significant. However, there was also no difference in the time spent in target blood glucose ranges between all of the groups. The T40 group had a higher starting blood glucose level, they required less extra carbohydrates prior to exercise and had a longer time before reaching hypoglycemia.

The authors concluded that decreasing basal insulin by 80% up to 40 minutes before exercise was still not enough in reducing exercise-induced hypoglycemia risk.

This study was very small and the results did not reach significance statistically. Further studies are required for more concrete evidence.