New research published in Diabetologia shows that saving one’s workout for later in the day may reduce insulin resistance by up to 25% compared with morning exercise, and although breaking up a day of sedentary time with periodic nonsedentary activities reduces cardiovascular risk, it did not seem to improve the outcome of insulin resistance.

While the authors promoted the need for further research in how the timing of physical activity may influence the occurrence of type 2 diabetes, they touted the advantage of the late afternoon peak in muscular strength as well as the metabolic function of skeletal muscle in improving insulin sensitivity.

Lead author Jeroen van der Velde from the Department of Clinical Epidemiology at Leiden University Medical Center, the Netherlands, and colleagues tested their hypothesis that the magnitude of the insulin-sensitizing effect resulting from physical activity depends on the timing of the activity, with up to 25% more benefit when conducted in the later afternoon or evening. The authors reported that the evening gain realized from participating in moderate-to-vigorous activity still leads when comparing the benefit of taking activity breaks throughout a day of sedentary time and maintains its edge even when comparing early morning exercise.

The team examined participants of the Netherlands Epidemiology of Obesity study (n = 775) and assessed sedentary time and breaks, with time defined as morning (06:00-12:00 hours), afternoon (12:00-18:00 hours), or evening (18:00-00:00 hours). Blood samples of all subjects were taken to measure both fasting and postprandial blood glucose and insulin levels. Lifestyle and demographic information were recorded after participants completed questionnaires. The team used activity sensors that determined the varying intensity of different physical activities, as well as liver fat content by magnetic resonance spectroscopy (n = 256), with moderate-to-vigorous-physical activity evenly distributed throughout the day (sleep time was excluded).

The demographic breakdown included 58% women with a mean (SD) age of all subjects 56 (4) years and SD BMI of 26.2 (4.1) kg/m2. The authors evaluated serum triacylglycerol concentrations and liver fat content as relevant because high-fasting serum triacylglycerol levels may be linked to higher concentrations of fat in the liver, which in turn is strongly associated with insulin resistance. Moderate-to-vigorous activity in the afternoon or evening was associated with a reduction of up to 25% in insulin resistance.

Insulin resistance was similar (–3% [95% CI: 25%, 16%]) in those most active in the morning when compared with subjects who had an equivalent amount of moderate-to-vigorous activity throughout the day. Insulin resistance was reduced in participants who were most active in the evening (–25% [95% CI: –49%, –4%]) or late afternoon (–18% [95% CI: –33%, –2%]). The team concluded that “The number of daily breaks in sedentary time was not associated with lower liver fat content or reduced insulin resistance. Moderate-to-vigorous activity in the afternoon or evening was associated with a reduction of up to 25% in insulin resistance. Further studies should assess whether timing of physical activity is also important for the occurrence of type 2 diabetes.”

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