- βAfternoon exercise avoids the post-workout blood sugar spike seen with morning HIIT in type 2 diabetes
- βRegular meal timing significantly reduced blood sugar variability in people with type 2 diabetes
- βStudy used continuous glucose monitors for precise, real-world blood sugar tracking across 48 participants
| Journal | Diabetologia |
| Year | 2025 |
| Authors | Keller, Brady, Smith |
| PMID | 40580209 |
What Was Studied β and Why It Matters
Researchers wanted to find out whether the time of day you exercise makes a difference to blood sugar control in people with type 2 diabetes. With more people using high-intensity interval training (HIIT) as a way to manage their condition, understanding when to work out could be just as important as the workout itself. This 2025 study published in Diabetologia is one of the first to directly compare morning versus afternoon exercise in both people with and without type 2 diabetes.
What the Researchers Did
The study followed 48 participants β 24 with type 2 diabetes and 24 without. Each person performed identical high-intensity interval exercise sessions twice: once at 9:00 AM and once at 4:00 PM, at least a week apart. Meals were carefully controlled the day before, day of, and day after each session. Continuous glucose monitors tracked blood sugar around the clock, giving researchers a detailed picture of how the body responded.
Key Findings in Plain English
- Morning exercise raised blood sugar in people with type 2 diabetes for up to two hours after the workout β in both men and women. Afternoon exercise did not cause this spike.
- Overall 24-hour blood sugar levels were similar regardless of when participants exercised, but the short-term post-exercise spike with morning workouts is still a concern for day-to-day management.
- Morning cortisol (a stress hormone) was naturally higher in all participants. In type 2 diabetes, this hormone can interfere with insulin's ability to lower blood sugar β likely explaining the morning spike.
- Inflammation markers were higher in the morning in people with type 2 diabetes. Specifically, C-reactive protein (a sign of inflammation) and NT-proBNP (linked to heart stress) were both elevated in the morning compared to afternoon.
- Eating regular, controlled meals reduced blood sugar swings significantly in people with type 2 diabetes, highlighting that consistent meal timing is a powerful tool alongside exercise.
What This Means for You
If you have type 2 diabetes and enjoy high-intensity workouts, scheduling them in the afternoon may help you avoid unwanted blood sugar spikes right after exercise. This doesn't mean morning movement is harmful β a gentle morning walk is still beneficial β but intense sessions may work better later in the day when your body's hormone environment is more cooperative.
Monitoring your blood sugar before and after exercise remains essential. If you use a continuous glucose monitor or test strips, tracking your response to different workout times can help you personalise your routine. MDS Diabetes stocks a wide range of glucose monitoring supplies to support exactly this kind of day-to-day self-management.
The study also reinforces something often overlooked: when you eat matters. Participants who followed regular, structured meal timing saw meaningful reductions in blood sugar variability β a reminder that diet habits and exercise timing work best as a team.
Bottom Line
Afternoon high-intensity exercise appears to be more effective than morning exercise for managing blood sugar in type 2 diabetes. Natural morning hormones β particularly cortisol β can blunt blood sugar control after intense workouts. Pairing afternoon exercise with consistent meal timing may offer the best results. Talk to your diabetes care team before making significant changes to your exercise routine, and use glucose monitoring tools to track how your body responds personally.