Scientists Link Timing of Exercise to Diabetes Risk

It's no secret that physical activity can do wonders for your physical and mental well-being. But the time of day you choose to exercise might influence the extent of these benefits.

In a recent study published in the journal Diabetologia, researchers from Harvard found that the time of day individuals choose to participate in physical activity can affect their risk of Type 2 diabetes.

Approximately 1 in 10 Americans have diabetes, 90 to 95 percent of whom have Type 2, according to the Centers for Disease Control and Prevention. Type 2 diabetes occurs when your body's cells become resistant to the hormone insulin, which is important in controlling blood sugar levels.

Physical activity can help individuals manage this condition as well as maintain a healthy weight, improve sleep and mood, and support a healthy heart. However, the Harvard team found that the type and timing of this exercise might matter.

The study looked at 93,095 individuals with a mean age of 62 years and without a history of Type 2 diabetes. Each participant was asked to wear an accelerometer on their wrist for one week to measure their movement and activity. This activity was categorized into three segments: morning activity (between 06:00 to 12:00); afternoon activity (between 12:00 to 18:00); and evening activity (between 18:00 to 24:00).

Six years later, the researchers recorded how many of these participants had been diagnosed with Type 2 diabetes. What they found was that those who had been physically active in the morning and afternoon had a significantly reduced risk of diabetes than those who mostly exercised in the evening.

This builds on a previous study, published in the journal Cell Metabolism in 2019, suggesting that our circadian rhythms may affect our ability to break down fat during exercise. Their study found that mice were more effective at breaking down fat during the early stages of their "active phase," which, for us, would be early in the morning.

However, these effects might also be dependent on the intensity of the exercise. When participants in the Harvard study engaged in more vigorous exercise, the protective benefits of the activity became more apparent across all time groups.

"Exercise, such as vigorous activity (really working up a sweat like running) or moderate to vigorous activity (like walking) were protective no matter the time of day," co-author Chirag Patel, an associate professor of Biomedical Informatics at Harvard Medical School, told Newsweek. "I think everyone who is like the individuals we studied (e.g., older, at risk for disease) could benefit from exercise at all times of the day."

The team also found that the consistency of exercise did not seem to matter so long as the total activity throughout the week was the same—in other words, going for a 20-minute run every morning had the same benefits as two 70-minute sessions at the gym.

"We found that total activity— as opposed to exercise as we think about it—was associated with less of a risk," Patel said.

Ultimately, exercise at any time can reduce your risk of Type 2 diabetes, especially if it is higher intensity. For gentler activity, concentrating it in the morning may help reduce your risk, but more work still needs to be done to confirm the optimal timing and frequency.