A recent study published in Obesity explores differences in the timing of moderate-to-vigorous physical activity (MVPA) and its impact on blood glucose levels and metabolic function in overweight and obese sedentary adults.

Study: Impact of lifestyle moderate-to-vigorous physical activity timing on glycemic control in sedentary adults with overweight/obesity and metabolic impairments. Image Credit: Nomad_soul / Shutterstock.com

How does the time of day affect glucose levels?

Obese people are more likely to develop impaired glucose tolerance, insulin resistance, and type 2 diabetes mellitus. Weight reduction through dietary management and physical activity (PA) is often recommended to improve glycemic control in obese individuals.

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

Physiological processes are regulated by circadian rhythms; therefore, blood glucose levels fluctuate throughout the day. Skeletal muscle is primarily responsible for clearing glucose from the blood, whereas reduced uptake by muscle cells during the afternoon and evening contributes to increased blood sugar levels at these times.

Thus, MVPA later in the day could improve glucose homeostasis. This has been demonstrated in previous studies examining night glucose and glycated hemoglobin (HbA1c) levels.

Previous studies have often focused on lifestyle physical activity (PA) in association with nocturnal and diurnal glucose levels, mostly during the fasting state and without regard to the timing. This motivated the current study, in which the timing of MVPA as part of daily life was assessed against glucose levels.

What did the study show?

The current study included 186 adults with a mean age of 46.8 years. Both males and females were equally represented. All study participants were either obese or overweight, with an average body mass index (BMI) of 32.9.

The study period of 14 days was classified into inactive days or days in which the participants were somewhat active, active, or very active based on World Health Organization (WHO) guidelines on physical activity. Activity was monitored using accelerometers, whereas glucose levels were recorded by continuous glucose monitoring devices.

The timing of activity was recorded as morning, afternoon, or evening PA, which reflected activity performed between 6:00 AM and 12:00 PM, 12:00-6:00 PM, and 6:00 PM to 12:00 AM, respectively. Mixed MVPA reflected PA without a clear timing.

Mixed MVPA accounted for more PA than any other timing group. The average MVPA was 24 minutes per day.

Some activity was associated with lower blood glucose levels, including 24-hour, diurnal, or nocturnal as compared to being inactive. More specifically, 24-hour mean glucose levels were 1.0 and 1.5 mg/dL lower during somewhat and very active days, respectively, as compared to inactive days. Likewise, nocturnal glucose levels were reduced by 1.5, 1.6, and 1.7 mg/dL on somewhat active, active and very active days, respectively.

Lower diurnal, nocturnal, and 24-hour blood glucose levels were reduced when MVPA was more frequently performed between 6PM and midnight. Morning and mixed MVPA patterns were not associated with any changes in blood glucose levels.

Both 24-hour and nocturnal blood glucose levels were lowest with evening exercise as compared to the inactive group. Overall, increased daily MVPA was associated with lower 24-hour and nocturnal glucose levels.

These improvements were particularly notable among both male and female participants with impaired glucose regulation. Moreover, with 150-300 minutes of MVPA every week, improved blood glucose control is achieved as compared with inactivity.

These findings highlight the promising area of MVPA timing as a novel approach to improve metabolic health in people at risk of developing cardiovascular diseases.”

Conclusions

The study findings suggest that accumulation of MVPA mostly during evening hours is associated with better stabilization of blood glucose levels among obese and overweight sedentary adults with impaired metabolism. Thus, both the optimal volume and timing of daily activity are crucial for maintaining glucose control.

These findings agree with earlier studies in which reduced insulin resistance was observed among adults with high BMIs who were most active in the afternoon or evening as compared to mixed or morning activity.

The mechanisms responsible for this association may involve increasing the efficiency of glucose uptake in skeletal muscle at a time when it is low, along with insulin sensitivity. Furthermore, nocturnal PA may upregulate circadian genes in skeletal muscle that are key to metabolic processes. Exercise may also increase the translocation of glucose transporter type 4 (GLUT-4).

Even among individuals with diabetes, evening exercise may enhance glycemic control as compared to morning exercise, which increases cortisol levels and subsequently induces hyperglycemia. In more active people, the observed effects could be greater.

Future research is needed to explore these patterns in older adults and diabetic individuals, who are at greatest need for euglycemic interventions.