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How you work out as well as when you exercise matters. MarcosMartinezSanchez/Getty Images
  • Researchers report that morning and afternoon exercise seem to correlate with lower diabetes risk.
  • They also found that more total exercise was more protective against diabetes
  • Experts say it’s unclear why the time you exercise matters, but risk protection factors may involve lifestyle or biological factors.

Exercise is strongly associated with lowering the risk of type 2 diabetes, but your level of protection may vary depending on when and how you work out.

A study published today in the journal Diabetologia concludes that while physical activity undertaken in the morning or afternoon seems to reduce the risk of type 2 diabetes, the same was not true of exercising in the evening.

The research led by Dr. Caiwei Tian of Harvard University and Dr. Chirag Patel of Harvard Medical School in Massachusetts also found that people who got more total hours of measurable physical activity were less likely to develop type 2 diabetes.

“The consistency or routine of physical activity was not strongly associated with type 2 diabetes,” the study authors wrote. “In other words, individuals who exercise a smaller amount of time more frequently are at no lesser risk for diabetes than individuals who exercise the same total amount, but with less of a routine.”

The study was based on data from 93,095 UK Biobank participants who had no history of type 2 diabetes and wore an accelerometer for one week to measure their physical activity. The activities included chores, walking, and vigorous exercise.

Diabetes risk assessments were adjusted based on lifestyle factors such as sleep and dietary intake.

Researchers measured activity based on metabolic equivalent of task (MET) hours and reported that for each one-unit increase of MET hour of physical activity, type 2 diabetes risk decreased 10% for morning (6 a.m. to noon) activity and 9% for afternoon (noon to 6 p.m.) activity.

No such correlation was seen for evening (6 p.m. to midnight) activity, however.

“The timing of activity may play a role in mitigation of diabetes risk,” the study authors noted. “The findings also suggest it is helpful to include some higher intensity activity to help reduce the risk of developing diabetes and other cardiovascular disease.”

“It’s pretty well known that physical activity is associated with less risk for cardiovascular disease and diabetes,” Patel told Medical News Today. “Some of the literature also suggest that timing matters.”

Patel said it was unclear why exercising in the evening seemed to be less protective. The possibilities could include factors overlooked or underemphasized in the study design, such as additional lifestyle or socioeconomic differences.

Future studies also may look at the “intersection with people’s chronotype” — whether they are “morning people” or “night owls” — and individual biological differences, he said.

“One possible explanation for this finding is that morning and afternoon physical activity may help regulate the circadian rhythm, which is the body’s natural clock that influences various biological processes, including metabolism, hormone secretion, and sleep quality,” said Dr. Alex Foxman, the medical director of Achieve Health and Weight Loss, a holistic weight-loss program. “By contrast, evening physical activity may disrupt the circadian rhythm and impair glucose tolerance, especially if it is done close to bedtime.”

“Another possible explanation is that morning and afternoon physical activity may reduce the amount of time spent in sedentary behaviors, such as sitting or lying down, which are known to increase the risk of type 2 diabetes,” Foxman told Medical News Today.

Foxman said the study “provides useful information for people who want to lower their risk of type 2 diabetes or improve their blood sugar control.”

“It suggests that they should aim to do at least 150 minutes of moderate to vigorous physical activity per week, preferably in the morning or afternoon, and avoid being sedentary for long periods of time,” he added. “They should also follow a healthy diet, get enough sleep, and consult their doctor if they have any concerns about their health.”

Dan Gallagher, a registered dietician with Aegle Nutrition, told Medical News Today that there “might be a slight advantage to the time you workout during the day.”

“However, the bigger point is that you’re working out at all,” said Gallagher. “Whatever time of the day helps you get your workout done is when you need to schedule your workout. Being mindful of your diet during the rest of the day will help you more when it comes to insulin resistance and the chance of developing diabetes.”

“Exercise is a great tool to prevent diabetes and the best workout is the one that’s completed,” he added. “Whatever time you need to workout each day to make it a regular practice is better than no workout at all.”