If you have type 1 diabetes, you may have faced dilemmas when deciding when and how much to exercise, and what kinds of exercise to do. While some research has shown that exercise helps people with type 1 stay within their recommended blood glucose range, there’s also a danger that exercise will lead to unpredictable drops or spikes in glucose levels. This means it’s especially important to know how your glucose levels respond to exercise at different times of the day — and how this response may change based on what you’ve eaten and what kind of exercise you’re doing. As a general rule, you’ll need to monitor your blood glucose more closely before and after exercise. Because of fears associated with the risk of hypoglycemia (low blood glucose) in particular, many people with type 1 diabetes don’t get enough physical activity.
One of the risks that’s often associated with exercise in people with type 1 is delayed hypoglycemia — a drop in your blood glucose that happens hours after you exercise. Some studies have shown that aerobic exercise causes this type of glucose drop more frequently than other types of exercise — but in a recent analysis that looked at levels throughout the entire day, this wasn’t found to be the case.
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Less risk of hypoglycemia over 24 hours
In a research review published in the journal Nutrition, Metabolism & Cardiovascular Diseases, researchers were interested in looking at trends in blood glucose levels over a 24-hour period in people with type 1 diabetes who did different forms of exercise. They looked at 12 different studies in which a total of 145 physically active participants used continuous glucose monitoring (CGM) systems, since these studies had the most data showing how glucose levels changed.
The researchers wanted to compare sustained aerobic exercise with both intermittent exercise and resistance exercise — but there wasn’t enough data on resistance exercise to include this type. They found that compared with sustained aerobic exercise, intermittent exercise increased the amount of time spent with hypoglycemia and reduced participants’ average glucose level. This average glucose reduction wasn’t necessarily a good thing, though, since it was due at least in part to hypoglycemia.
There were no differences between the two types of exercise in the amount of time spent with high blood glucose, or in the proportion of people who experienced hypoglycemia. This means that compared with intermittent exercise, sustained aerobic exercise didn’t lead to fewer people having hypoglycemia — but it did reduce the amount of time spent with low blood glucose in cases where this happened.
The researchers also noticed a reduced risk of hypoglycemia — based on the amount of time spent with low glucose — when participants exercised in the morning, compared with exercising in the afternoon. Morning exercisers also had better glucose control on the following day, as noted in a Healio article on the study.
“In light of this, exercise in the morning is encouraged while more attention [to glucose levels] will be necessary if endurance is performed in the afternoon,” the researchers wrote. “If people with diabetes know that a certain behavior will increase the risk of experiencing hypoglycemia, together with the timeframe in which it is more likely to happen, they could adopt strategies to prevent it.”
Limited benefit from reducing rapid-acting insulin
Another finding in the analysis was that reducing doses of rapid-acting insulin around the time of exercise led to a lower risk of hypoglycemia during an eight-hour period after sustained aerobic exercise. Based on other studies, the researchers noted that a reduction of about 50% of the typical dose of rapid-acting insulin seems to have the best results. After eight hours, though, there was no reduced risk of hypoglycemia associated with reducing the dose of rapid-acting insulin.
The researchers wrote that more research is needed on the effects of different types of exercise on hypoglycemia — especially well-designed studies that directly assign participants to do different kinds of exercise. These studies, they noted, should have a standard threshold for hypoglycemia, keep track of the time of day when people exercise, and include a group that doesn’t exercise for comparison.
Talk to your doctor about strategies to prevent hypoglycemia if you experience it on days when you exercise, or if you don’t exercise as much as you should because of the risk of hypoglycemia. Any strategy that involves changing the amount of insulin you take should also be implemented only after discussing this strategy with your doctor.