Nighttime exercise improves glucose control in overweight individuals

A recent study published in the journal Obesity examines how time spent in moderate-to-vigorous physical activity (MVPA) affects blood glucose levels and metabolic function in sedentary overweight and obese adults.

How does time of day affect glucose levels?

Obese individuals are more likely to develop impaired glucose tolerance, insulin resistance, and type 2 diabetes. To improve glycemic control in these patients, weight loss through dietary management and physical activity (PA) is often recommended.

MVPA is effective in maintaining glucose homeostasis in overweight or obese individuals. However, the optimal timing of MVPA remains unclear.

Physiological processes are regulated by circadian rhythms, so blood glucose levels fluctuate throughout the day. Skeletal muscle is primarily responsible for removing glucose from the blood, while decreased uptake by muscle cells in the afternoon and evening contributes to higher blood sugar levels at these times.

Thus, MVPA later in the day may improve glucose homeostasis, as demonstrated in previous studies examining nocturnal glucose and glycated hemoglobin (HbA1c) levels.

Previous studies have focused on physical activity in general, without regard to time of day. This motivated the current study, which assessed the impact of timing of MVPA on glucose levels.

What did the study show?

The study involved 186 adults with an average age of 46.8 years. The participants included both men and women. All participants were overweight or obese, with an average body mass index (BMI) of 32.9.

The study period lasted 14 days, which were classified as low activity days, moderately active days, active days or very active days according to the World Health Organization (WHO) recommendations for physical activity. Activity was monitored using accelerometers and glucose levels were monitored using continuous glucose monitoring devices.

Activity was recorded as morning, afternoon, or evening, reflecting activity between 6:00 AM and 12:00 PM, 12:00 PM and 6:00 PM, and 6:00 PM and 12:00 AM, respectively. Mixed MVPA included physical activity with no specific time.

Research results

Some activity was associated with lower blood glucose levels, including 24-hour, daytime, and nighttime levels compared with low activity. Specifically, mean 24-hour glucose levels were 1.0 and 1.5 mg/dL lower on moderately active and very active days, respectively, compared with low activity days. Similarly, nighttime glucose levels were reduced by 1.5, 1.6, and 1.7 mg/dL on moderately active, active, and very active days, respectively.

Glucose levels were lower when MVPA was performed more frequently between 6:00 PM and midnight. Morning and mixed MVPA patterns were not associated with changes in glucose levels.

The study shows that performing MVPA in the evening is associated with more stable glucose levels in sedentary overweight and obese adults. These results are consistent with previous research that has found reduced insulin resistance in people with a high BMI who were most active in the afternoon or evening.

The mechanisms responsible for this association may include increased efficiency of glucose uptake by skeletal muscle and increased insulin sensitivity. Nocturnal physical activity may activate circadian genes in skeletal muscle that are key to metabolic processes. Exercise may also promote glucose transporter type 4 (GLUT-4) trafficking.

Future studies are needed to examine these patterns in older adults and patients with diabetes who require optimal glycemic intervention.