What Time You Work Out May Affect Blood Sugar Control

• New research suggests that exercising in the morning, afternoon, or evening may influence blood sugar regulation.
• The study’s lead author explains why the timing of exercise may matter as much as how often or how hard you train.

Blood sugar control is important for people living with diabetes, but it also plays a major role in overall health. Research shows that glucose levels can affect several bodily functions, including hormone balance, body composition, digestion, and even brain health.

For that reason, keeping blood glucose in check matters, and one way to help may be doing moderate- to vigorous-intensity exercise in the evening, according to a study published in Obesity.

Researchers studied 186 men and women who were overweight or had obesity and had at least one metabolic issue, such as high blood pressure or high cholesterol. Over a 14-day period, they monitored physical activity, glucose levels, and the time of day people exercised. Morning workouts were defined as those done before noon, afternoon exercise as taking place between noon and 6:00 p.m., and evening exercise as occurring after that.

By the end of the two weeks, participants who completed more than half of their exercise in the evening had significantly lower glucose levels than sedentary participants, and they also showed better glucose regulation than those who mainly worked out in the morning or afternoon.

The benefits were especially clear among people who had difficulty controlling blood sugar before joining the study, according to co-author Antonia Clavero Jimeno, Ph.D.(c), a researcher in the department of physical education and sports at the University of Granada in Spain.

Although the participants were selected because of metabolic concerns and inactive lifestyles, Clavero Jimeno told Bicycling that earlier evidence suggests similar results may apply to people without those risk factors who already exercise regularly.

“In fact, the impact of both physical activity volume and timing for glycemic control may be amplified in those with higher activity levels,” he said.

That idea is supported by earlier research involving active people whose blood sugar changes were measured based on workout timing. In that study, published in 2022, people who did moderate-to-vigorous exercise in the afternoon had 18 percent lower insulin resistance than morning exercisers, while the evening group did even better, with a 25 percent drop in insulin resistance.

One factor neither study examined was diet, and Clavero Jimeno said this is an area that needs more research. He said a key next step is to determine whether time-restricted eating, also known as intermittent fasting, would help or hurt glucose regulation when combined with evening exercise. His team is already studying that question. Some research published this year suggests intermittent fasting may have promising effects on blood sugar regulation, at least for people with type 2 diabetes.

“Dietary intake is, of course, recognized as crucial for glycemic control, and may influence the results overall,” Clavero Jimeno said. “But in the absence of that information, this current study does emphasize that if you want better control of your glucose levels, evening exercise, done at a higher intensity, may be beneficial.”