Reduced Insulin Dose After Exercise Helps Avert Hypoglycemia

Marlene Busko

March 28, 2013

A small study of patients with type 1 diabetes has shown the merits of greatly reducing the dose of insulin taken after as well as before exercise, to avoid hypoglycemia.

Patients who took a 25% dose of insulin before running on a treadmill for 45 minutes and then took a 50% dose of insulin an hour later were protected from hypoglycemia during or soon after exercise. They were, however, still at risk for a dangerous drop in blood glucose later that evening.

"It's been well-known that people with type 1 diabetes need to heavily reduce their insulin before exercise, but now we showed that it's important to reduce it after exercise," lead author Daniel J. West, PhD, from Northumbria University, Newcastle-upon-Tyne, United Kingdom, told Medscape Medical News.

"The patients and nurses and clinicians do get a little cautious when having patients reduce their insulin dose, and patients do get quite uncomfortable eating a meal and not taking enough insulin, so it's really surprising for us that they really do have to heavily reduce their insulin dose," Dr. West said.

However, even with this insulin-dose-adjustment strategy, "Patients need to be aware that they are not fully protected for the entire day," he added.

The study was published online March 20 in Diabetes Care.

Two Periods of Vulnerability

People with type 1 diabetes who are physically active live about 10 years longer than those who are not active, but avoiding low blood sugar surrounding exercise remains challenging, Michael Riddell, PhD, from York University, Toronto, Ontario, who was not involved in this study, told Medscape Medical News.

"There are 2 periods of vulnerability: the low blood sugar that occurs during exercise and…typically 7 to 11 hours after exercise, normally when the patients are asleep," he noted. The patients may not wake up, and the hypoglycemia could even lead to convulsions and loss of consciousness.

Investigators have tried for years to come up with the right prescription for adjusting insulin doses surrounding exercise, he added.

In this study, Dr. West and colleagues enrolled 11 young men with type 1 diabetes who had a mean age of 24 years and participated in regular aerobic exercise.

The patients attended a lab on 3 mornings. In each experiment, they ate a standardized breakfast and gave themselves a guideline-recommended 25% dose of rapid-acting insulin an hour before they ran on a treadmill for 45 minutes. An hour later, they ate a standardized meal and self-administered a full, 75%, or 50% dose of rapid-acting insulin. Patients wore a continuous glucose monitoring system for 20 hours after they left the lab.

Within 3 hours of exercise, 5 patients who had received the full insulin dose and 2 patients who had received the 75% insulin dose had hypoglycemia (glucose 3.9 mmol/L or less). During the evening and night after the exercise, 6 patients who had received the 75% dose of insulin, 6 patients who had received the full dose, and 3 patients who had received the 50% dose had hypoglycemia.

"Half the Problem Licked"

"It's almost like [these researchers have] half the problem licked with this type of insulin therapy — [a 25% insulin dose with the preexercise meal and a 50% insulin dose in with the postexercise meal] — but there's still some way to go to prevent this type of low blood sugar that occurs at night when [the patients] are sleeping, " Riddell said.

To avoid a risk of hypoglycemia in late recovery after exercise, patients with type 1 diabetes may need to have a bedtime snack or alter their basal insulin dose, he said.

The authors have reported no relevant financial relationships.

Diabetes Care. Published online March 20, 2013. Abstract