The effect of exercise on glucose control for people with type 1 diabetes

It has been clear for many years that, for an individual with type 1 diabetes to achieve good glucose control and reduce the risk of diabetes-related complications, they need to become an expert on how insulin therapy works for them as an individual. This knowledge is not something that is simply acquired with time but needs to be taught. Understanding how the food we eat influences blood glucose, and particularly how to assess the carbohydrate content of a meal, is an important skill for the person with diabetes. DAFNE (Dose Adjustment for Normal Eating) and a number of similar courses teach small groups of people how to “carbohydrate count”. There is considerable variation between individuals in how a particular meal will influence their blood glucose, and there will also be variation within an individual on how a particular meal may act, but the general principles can be taught. The person with diabetes can then use that knowledge to become expert in managing insulin therapy with meals.

The effects of exercise on blood glucose are also taught in carbohydrate counting courses. This is an area that is perhaps more difficult to give specific advice on, as the effects of exercise vary greatly. The type of exercise, the duration of exercise, the physical fitness of the individual, and how much and what type of insulin they have injected will all influence how much blood glucose will fall and, importantly, how long it will fall for. The published evidence to date has been a mixture of very carefully controlled laboratory experiments with tightly managed exercise regimens and real-world data from less controlled studies. As with carbohydrate counting, although the effect of exercise varies between people, there are general principles that can be taught. The type of exercise will affect what immediately happens during exercise. Lower-intensity (aerobic) exercise will lower glucose during the activity and for a period afterwards, while higher-intensity exercise may raise glucose during the exercise period before lowering it afterwards.

The study by Riddell and colleagues is a helpful addition to our knowledge. It was a large study conducted in real-world conditions but combined this with relatively specific exercise programmes. Participants were instructed to watch one of three exercise videos and complete at least six sessions over 4 weeks. The exercise was classified as aerobic, interval (higher-intensity) or resistance activity. The study participants included individuals using hybrid closed-loop therapy, insulin pump therapy and multiple daily injections. The outcome measures included glucose sensor-derived time in range.

The main use of the study is the detail of how the type of exercise interacted with other measures that we know influence glucose control. One of the striking features was the variability in the effect of exercise between participants, and the authors comment that there was also marked variation within each individual. Although it is possible to talk in general terms about the effects of a specific type of exercise, the individual will have to adapt that knowledge to their own experience. The effects are not simple; it would be a mistake to over-simplify training about exercise and diabetes.

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