Getting regular physical activity — especially aerobic exercise, or cardio — has been shown to help people with diabetes control blood glucose levels, at least on the days when they exercise. It’s believed that aerobic exercise makes your cells more sensitive to insulin, letting your body use glucose as fuel more efficiently — something that may be true for many people with both type 1 and type 2 diabetes.
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So regular activity is important — but that still leaves lots of questions about the best way to exercise. Many people, of course, will do a form of exercise that they enjoy at a time that works for them. But a new study suggests that when it comes to blood glucose control, all times of the day aren’t equally good for exercise.
Better blood glucose control, less belly fat
The study, published in the journal Physiological Reports, examined the effects of exercising at different times of the day in 32 men who were deemed at risk for type 2 diabetes. Each participant completed 12 weeks of supervised exercise training consisting of stationary cycling, either in the morning (between 8 and 10 a.m.) or in the afternoon (between 3 and 6 p.m.). The average age of the participants was 58, and each exercise program was as close as possible to the others, allowing for individual differences.
Researchers found that compared with participants who exercised in the morning, those who completed the afternoon program had greater insulin sensitivity, better fasting glucose levels (an average drop of 5.4 mg/dl by the end of the program, compared with an increase of 9.0 mg/dl), better exercise performance, and greater loss of body fat (an average loss of 1.2 kilograms or 2.6 pounds, compared with a loss of 0.2 kilograms or 0.4 pounds).
The researchers concluded that people with impaired glucose metabolism — which may also include people with diabetes, although they didn’t take part in this study — might benefit from improved metabolic benefits if they exercise in the afternoon. While the study didn’t explore why this apparent benefit from afternoon exercise took place, it’s well known that our metabolism changes throughout the day as part of our circadian rhythm, or “biological clock.” That means levels of many different hormones and other substances will vary in our body throughout the day.
Findings in sync with earlier study
As noted in a New York Times article on the latest study, the results complement the findings of a 2019 study, published in the journal Diabetologia. That older study involved a small group of men with type 2 diabetes who were randomly assigned to complete a high-intensity interval training (HIIT) exercise program in either the morning or the afternoon for two weeks. After a two-week break, participants then did the same program during the other time of the day. Afternoon workouts were found to significantly improve blood glucose control, while morning workouts actually led to unhealthy blood glucose spikes.
The newer study, which involved more moderate exercise, also found that afternoon activity lowered participants’ blood glucose, while morning activity raised it — demonstrating that this difference wasn’t limited to high-intensity workouts. The researchers noted that in future studies, they would like to explore the “molecular effects” in the body that may be responsible for the different effects on blood glucose and body fat from morning and afternoon workouts. They also would like to add evening workouts to the mix, to see if those later workouts would be more of less effective that afternoon exercise.
While exercising at any time of day is likely to have some health benefits, this study — and the older one from 2019 — show that you should watch out for higher blood glucose if you exercise in the morning, and possibly consider switching the timing of your exercise routine if you aren’t getting the benefits you want from it.
Want to learn more about exercising with diabetes? Read “Add Movement to Your Life,” “Picking the Right Activity to Meet Your Fitness Goals” and “Seven Ways to Have Fun Exercising.”