When you have type 1 diabetes, trying to manage the unpredictability of blood sugars with exercise can be a source of frustration and confusion. Often the most difficult aspect to manage is preventing late-onset hypoglycemia.
Imagine that you’ve just had an exhilarating day of cycling. With careful planning, a lot of hard work and a little luck, your blood sugars have been good all day. Crawling into bed and falling asleep feels glorious. Best day ever! Then you’re dreaming that you’re racing in the Tour de France. You’re climbing a mountain but you’re so exhausted that you’re shaking uncontrollably. You’re sweating through your jersey. You bolt awake and it’s the middle of the night. You’re not racing your bike. You’re having a low blood sugar reaction. You think, ‘Why did this happen? My sugars were good all day!’
Night-time hypoglycemia after exercise is common for people with type 1 diabetes. One of the causes of late-onset hypoglycemia is that the body is more sensitive to insulin after exercise, and this effect can last for 24 to 48 hours. The more intense and prolonged the activity, the longer and greater the insulin sensitivity. As well, muscles need to replenish their energy stores (called glycogen) following long duration exercise, and if sufficient carbohydrate is not consumed in the hours following exercise, then hypoglycemia may result. While it is true that there is no way to absolutely prevent low blood sugar, there are some effective strategies to reduce the risk of late-onset hypoglycemia after exercise.
- Reduce insulin dose by about 50% for the meal following exercise.
- If you wear an insulin pump, set a temporary basal rate for about six hours, starting at bed time. Decrease the hourly rate by about 20%.
- If you are on multiple daily injections, decrease your basal insulin by 20% on the day of exercise.
- If you do sustained aerobic exercise, you will likely require a more substantial reduction in insulin dose and a higher carbohydrate intake than if you do a short-term high intensity interval training session.
- There seems to be an increased risk of night-time hypoglycemia following afternoon exercise. Consider a larger insulin dose reduction following afternoon exercise.
Bedtime snack strategies
- Have a snack that is low glycemic index, such as a fruit smoothie (dairy-based), a yogurt drink, or fruit mixed with yogurt. Studies have shown that dairy products (for example, chocolate milk) consists of a ratio of carbohydrate to protein that is beneficial for replacing muscle glycogen and promoting rehydration. If you are lactose intolerant, options include nuts and seeds (for example, almonds, peanuts or pumpkin seeds) and soy milk. Lactose-free yogurt or dairy options are also available. Either one, or half a whole grain sandwich made with peanut butter and jam or leftover chicken is another good option.
- The snack size should be about 0.4 grams of carbohydrate per kilogram of body weight. This means that if you weigh 130 pounds, the snack should contain about 24 grams of carbohydrate. If you weigh 175 pounds, the snack should contain about 32 grams of carbohydrate.
- Eat the snack without taking rapid insulin.
- Be aware that drinking alcohol after exercise – even with food – substantially increases the risk of hypoglycemia.
Snacks alone, without changing basal insulin, do not seem to be as effective at decreasing the risk of lows during the night. Going to bed with a slightly elevated blood glucose concentration after a bedtime snack and a reduction in basal insulin dose would be expected to minimize hypoglycemia risk. Aggressive post-exercise insulin corrections near bedtime increase the risk of late-onset hypoglycemia and may contribute to severe hypoglycemia.
Be extra cautious when correcting post-exercise higher blood sugars, especially close to bedtime. Check sugars during the night (at 2:00 or 3:00 am) or use a real-time continuous glucose monitoring system with alarms and automatic pump suspension. If you are at high risk of severe night-time low blood glucose (i.e. you have recurrent hypoglycemia or you sleep alone), this additional blood sugar check is crucial.
Both decreasing insulin doses and increasing carbohydrate intake can help minimize the chance of having delayed-onset hypoglycemia. Remember, there will be some trial and error. Keep good records and analyze them with the help of your healthcare team. Checking blood sugars frequently will help you determine the strategy that works best for you. Don’t let your experience with low blood sugar or your fear of low blood sugar prevent you from being active.