Afternoon or evening physical activity is associated with reduced insulin resistance

Abstract

Exercise is an important strategy to improve metabolic outcomes and to reduce risk of developing type 2 diabetes. Previous studies have shown that frequent interruptions of extended sitting with standing or light physical activity reduced triacylglycerol levels – elevated triacylglycerol levels is linked to higher concentrations of fat in the liver, which in turn is strongly associated with insulin resistance. Previous studies have demonstrated that exercise is linked to reduced liver fat and improved insulin sensitivity but the timing of physical activity throughout the day may be a factor in metabolic health. Pre-clinical studies have shown daytime-dependent changes in exercise capacity and metabolic risk markers but few such investigations have been performed in humans.

In a study published in Diabetologia, data from the Netherlands Epidemiology of Obesity (NEO) study, a population-based prospective cohort study was used to investigate processes involved in the development of obesity-related diseases. Study participants had a self-reported body mass index (BMI) of >27 kg/m², aged between 45 and 65 years resulting in a study population of 6,671 individuals. Participants underwent a physical examination during which blood samples were taken to measure fasting and postprandial blood glucose and insulin levels, while demographic, lifestyle and clinical information were obtained via questionnaire. 35% of participants underwent MRI study to have their liver fat content measured. A further random subsample of 955 participants were given a combined accelerometer and heart rate monitor to wear for four consecutive days and nights to monitor movement and activity. Analysis of results obtained from 775 participants for whom complete data sets were available. After adjusting for variables such as age, sex, ethnicity and total body fat, the researchers observed that higher total Physical activity Energy Expenditure (PAEE) were associated with both reduced liver fat content and reduced insulin resistance. An association was also found between insulin resistance and the timing of moderate to vigorous physical activity (MVPA) during the day: performing MVPA in the afternoon or evening was linked to reduced insulin resistance, by 18% and 25% respectively, compared to an even distribution of activity throughout the day, even after adjustment for total amount of MVPA. There was no significant difference in insulin resistance between morning activity and activity spread evenly over the day. These results suggest that timing of physical activity throughout the day is relevant for the beneficial effects of physical activity on insulin sensitivity and should be incorporated into physical activity recommendation. Further studies should assess whether optimal timing of physical activity reduced the occurrence of type 2 diabetes and underlying mechanism for this.