When is it better to exercise for blood sugar: morning or evening? The wrong timing can spike your blood sugar

Exercise is recommended for blood sugar control, but the time of day can change the effect. According to recent research, in some cases, intense exercise at the wrong times can temporarily raise blood sugar levels.

Researchers from the Karolinska Institutet in Stockholm and the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen analyzed the results of several studies that compared the effects of morning exercise with those of exercise later in the day. The large review, published in March 2026 in the journal Trends in Endocrinology and Metabolism, found that for people with type 2 diabetes, exercise can either have a favorable effect on blood sugar or do more harm than good, depending on the time of day when the workouts are performed.

“Afternoon or evening moderate-to-vigorous exercise consistently improves glycemic control and insulin sensitivity in people with type 2 diabetes, whereas morning exercise has little effect or may worsen metabolism by raising blood glucose levels,” the authors write.

According to the analysis, the effect appears to be intensity dependent. Light walks, brisk walking or recreational activities do not produce the same effects. So, it is not the time itself that is the problem, but the combination of time, intensity and metabolic state of the body at the moment of effort.

Insulin resistance, a more widespread problem than thought

Insulin resistance, the stage that often precedes type 2 diabetes, can develop for years without obvious symptoms.

Many people may have this problem without knowing it, experts point out. “A good blood sugar, evaluated on an empty stomach at a given time, can fool you,” said Dr. Oana Pop, specialist in diabetes, nutrition and metabolic diseases.

Dr. Pop explains where the catch is: there are few cases in which the diagnosis can be made based on an empty stomach glucose alone. This explains why many people end up being diagnosed only with the onset of symptoms, directly with type 2 diabetes, although insulin resistance has been installed for a long time.

What happens in the body in the morning

The reason why morning exercise has a different effect on diabetics is due to what endocrinologists call the “dawn phenomenon” (dawn phenomenon). In the first hours after waking up, the level of cortisol, the stress and alertness hormone, rises in everyone, regardless of whether the person has diabetes or not. This hormone helps the body to come out of rest, but at the same time it tells the liver to release glucose from its reserves so that the body has energy to start the day.

In a healthy person, the pancreas immediately responds with an appropriate secretion of insulin, which pushes the sugar into the muscles, where it is used as fuel. In patients with type 2 diabetes, the pancreas produces less insulin and the cells are resistant to its action. For this reason, blood sugar is already higher in the morning, just when insulin resistance reaches high levels.

Harriet Wallberg-Henriksson, professor of physiology at Karolinska Institutet and lead author of the paper, explained to The Washington Post that when a person with diabetes starts jogging or pedaling vigorously first thing in the morning, the already elevated cortisol rises even more. The muscles ask for fuel, the liver releases additional glucose, but it is no longer used properly, because the cells refuse it. As a result, blood sugar rises and insulin sensitivity decreases for several hours.

“These conditions make morning exercise less favorable for the regulation of glucose metabolism in people with type 2 diabetes,” said the researcher.

In the afternoon, the best time for sports

Between 16:00 and 19:00, cortisol drops to its daily minimum, body temperature is near its peak, muscle strength is at its maximum, and insulin receptors respond better.

In one of the studies cited in the review, middle-aged men with type 2 diabetes did the same type of intense exercise at two different times of the day, in the morning and in the afternoon. When they exercised in the afternoon, their blood sugar dropped and stayed at better levels until the next day. When they repeated the same effort in the morning, blood sugar increased and insulin sensitivity decreased for several hours.

The authors of the review also report that afternoon exercise by patients with type 2 diabetes is associated with lower levels of cortisol and inflammation markers, as well as better muscle oxidative capacity compared to morning exercise.

Physical exertion can also regulate the body's internal clock

The authors point out that exercise is one of the most powerful factors that can regulate the biological clock, along with light, dark and meal times. Specialists call these factors “zeitgeber”, a German term for external cues that help the body match its internal rhythms. Every cell and every organ has its own molecular clock, and the brain coordinates everything through a central clock.

In people with type 2 diabetes, this coordination is often disrupted. Specialists talk about a circadian imbalance, a state in which the biological clocks are no longer well synchronized with each other. In these conditions, some metabolic processes start too early, too late or no longer work as they should.

Precisely for this reason, the ideal time to exercise is of clinical importance for people with blood sugar problems, not just for performance athletes. An analysis published in The Journal of Clinical Endocrinology & Metabolism reached similar conclusions and demonstrated that individualized exercise recommendation, including the time of day when it is practiced, can be part of the treatment strategy.

Movement, a real medicine, regardless of the time

Juleen Zierath, physiologist at Karolinska Institutet and one of the authors of the review, points out that “the most important message remains that physical exercise done at any time is better than no movement”.

And Wallberg-Henriksson adds that for those with type 2 diabetes who prefer morning exercise, it's wiser to keep the intensity low. “Light physical activity, such as brisk walking, does not appear to produce the same time-of-day effect” as intense exercise, the researcher explained. In other words, a half-hour walk after breakfast does not have the same impact as a fast run or a high-intensity bike ride, when blood sugar is already high.

What is not yet known about the ideal time for sports

The authors acknowledge that many of the studies included in the review were small, followed patients for short periods of time and relied mostly on middle-aged men. It is not yet clear whether the logic applies equally to women, the elderly or patients with type 1 diabetes.

Also, the analysis focused almost exclusively on blood sugar, but time of day could also influence cardiovascular risk, sleep quality or longevity, areas that remain open for future research.

In addition, individual chronotype, meaning everyone's tendency to function better in the morning or in the evening, could change the calculation. A morning person might have a slightly different hormone profile than a “night owl”, and future personalized recommendations will likely take this into account as well.