There are more than 3m people in the UK living with diabetes, amounting to 6% of the population. Of those, 10% or about 300,000 have type 1 diabetes, which usually develops during childhood and adolescence – as opposed to type 2, which tends to affect older adults and is more commonly associated with lifestyle and obesity.
Type 1 diabetes is an autoimmune disease that destroys the insulin–producing cells in the pancreas, preventing the body from producing the insulin that it needs to maintain the right level of blood glucose. People with type 1 diabetes are always treated with insulin injections or an insulin pump, without which they would die. The most common treatment is the basal-bolus regimen, which involves injecting a 24-hour-acting insulin once or twice daily to provide background insulin, along with fast-acting insulin injections before meals or snacks.
If the insulin dose is not right for the patient, they can have hypoglycaemia (low blood-glucose) or hyperglycaemia (high blood-glucose). For people living with type 1 diabetes, the risk of hypoglycaemia is a day-to-day phenomenon. Symptoms include light headedness, tremors, confusion, unsteadiness, drowsiness and sometimes unconsciousness. It happens quickly, making it one of the most feared complications from diabetes.
Hypoglycaemia is an acute emergency which needs immediate treatment with glucose – unlike hyperglycaemia, which can produce symptoms like excessive tiredness and large amounts of urine but only becomes an emergency if it continues for a few days. Both complaints are usually caused by taking too much insulin, increased exercise or not eating enough carbohydrates, so it is essential to strike the right balance between them.
The risks of exercise
Although we know that a patient’s level of exercise is a key variable in deciding how much insulin they need, there been very little research into how to maintain glycaemic control while exercising. This partly explains why people often avoid exercise for fear of a hypoglycaemic attack. If they are already hypoglycaemic at the start of an exercise session, they can’t begin until they have consumed carbohydrates and waited until their blood glucose has risen to an acceptable level. Even then, they may experience a further episode while exercising, which can impinge on their performance and potentially force them to stop. There is also a risk of post-exercise hypoglycaemia, especially for afternoon and evening activity.
Patients commonly worry about a hypo happening during the night, which can be particularly unpleasant. The patient will often only be woken up once the symptoms have reached a more acute point than it would take for them to notice had they been awake, meaning that they tend to feel worse as a result. Sometimes the patient might sleep through the symptoms altogether, which can eventually lead to a serious condition called hypo unawareness, where they will have a severe episode with possible unconsciousness without noticing any symptoms. Yet there has been no evidence until now to confirm the link between exercise and these night-time hypo attacks.
My co-researchers and I decided to conduct a study to help people with type 1 diabetes to be more confident about taking exercise. We created a set of insulin/carbohydrate instructions for nine patients (five male, four female) taking moderate-intensity exercise before their evening meal. The instructions were based on our best information about how to manage blood glucose, carbohydrates and exercise.
We measured how effectively these instructions maintained acceptable glucose levels in each participant during and after two exercise sessions one week apart. For each exercise session, we tested each participant’s blood glucose at ten regular intervals. All participants used a basal-bolus analogue insulin regimen and exercised regularly, and each participant reduced the dose of fast-acting insulin that they were required to take before their evening meal by 30% – the sort of substantial cut that patients would not normally consider without medical advice. Even then, we found that they became hypoglycaemic on a number of occasions at night, and were unaware of this in about half of them.
We found that the nine participants were in the acceptable glucose range just over half of the time, and hyperglycaemic almost 40% of the time. They were hypoglycaemic in the remaining 5% of tests, mostly between eight and 12 hours after exercising – at night, in other words. These responses were fairly evenly distributed across the people who participated. We concluded that the main risk from moderate-intensity exercise in the evening was delayed hypoglycaema during the night.
From our results, we were able to put together a set of instructions for people with type 1 diabetes taking exercise (contact me through my profile for the full set). To get a better understanding of how their body responds, patients should monitor their blood glucose before and after exercise, after their evening meal and before bedtime, and then before breakfast the following morning. They may need to reduce evening meal insulin dose by 30%-50%, and also have a carbohydrate snack at bedtime. It could also help to occasionally set an alarm and check their blood glucose between eight and 12 hours after their evening meal.
Our work to date has just been a pilot study. More research needs to be done with a larger group of participants with type 1 diabetes to see if it produces the same results. It would also be worth testing type 2 diabetics on the basal-bolus regime, since in principle they should enjoy similar benefits. With those caveats in mind, our hope is that by trying these strategies and keeping a close eye on how the body responds, people with type 1 diabetes should at last be able to exercise safely.