Comparing Long-acting Insulins During Exercise in Type 1 Diabetes

Exercise is an important part of a healthy lifestyle, and many people with Type 1 Diabetes like to take part in regular sport and exercise. The majority of people with Type 1 Diabetes are treated with a "basal bolus" insulin regimen, with background insulin provided by long-acting "basal" insulin doses, and "bolus" doses of short-acting insulin used to accompany food intake. Evidence shows that the main factor preventing people with diabetes from pursuing a more active lifestyle is fear of low blood glucose (hypoglycaemia). A previous study has shown that the type of background insulin affects the likelihood of an individual suffering hypoglycaemia during exercise and for 2 and a half hours afterwards. The aim of this study is to examine this further. The two most commonly used long-acting insulins, insulin glargine and insulin detemir, will be compared. Previous data suggests that there is a greater likelihood of hypoglycaemia with insulin glargine than insulin detemir. Exercise intensity can have an influence on the likelihood of hypoglycaemia, and in this previous study exercise intensity was measured using heart rate. This study will use a more formal definition of exercise intensity. The investigators will study blood glucose during exercise, but also metabolism as measured by hormones affecting blood glucose levels as well as markers of fat metabolism. The investigators will also use a continuous glucose monitoring system (CGMS) to consider hypoglycaemia on thei night following exercise as this is a recognised consequence of exercise in type 1 diabetes. The null hypothesis to be tested in this study is that there is no difference between the two insulins in their effect on blood glucose levels and metabolism during exercise and rates of nocturnal hypoglycaemia after exercise.