Abstract
Objectives:Night shift workers are at cardiometabolic risk due to circadian misalignment. We investigated whether infrequent exercise before each night shift that intentionally would not improve physical performance improves glucose tolerance and 24-h blood pressure profiles and synchronizes circadian rhythms of melatonin and cortisol in rotating night shift workers.Methods:A total of 24 rotating night shift workers (mean age, 35.7 ± 11.8 years) were randomized to exercise or no intervention. Workers in the exercise group performed 15.2 ± 4.5 exercise sessions within 2 h before each night shift. Before and after 12 weeks of exercise intervention and 12 weeks after the intervention, spiroergometry, oral glucose tolerance testing and 24-h blood pressure profiles were performed. Plasma melatonin and cortisol levels were measured in 3-hourly intervals during one 24-h period on each study day.Results:Exercise did not significantly change serum glucose nor insulin levels during oral glucose tolerance testing. Timed physical exercise had no effect on physical performance, nor did it change the circadian rhythms of melatonin and cortisol or influence 24-h blood pressure profiles.Conclusion:Physical exercise before each night shift at a low intensity level that does not improve physical performance does not affect circadian timing, glucose tolerance or 24-h blood pressure profiles in rotating night shift workers.
Highlights
The rates of obesity and type 2 diabetes mellitus (T2DM) are increasing1 [International Diabetes Federation (IDF)Diabetes Atlas 2017]
There are no studies in human subjects that causally relate clock genes to the development of T2DM, epidemiological data have shown that shift workers – who are known to experience disrupted circadian rhythms5 – are at increased risk of developing cardiometabolic disease.[6,7]
The night shift workers had a median duration of work including night shifts of 8.0 years [interquartile range (IQR), 4.3–21.0]; their median number of night shifts per month during their current occupation was 6.0 (IQR, 5.0– 7.0)
Summary
The rates of obesity and type 2 diabetes mellitus (T2DM) are increasing1 [International Diabetes Federation (IDF)Diabetes Atlas 2017]. Genetic disruptions in circadian clock genes lead to the development of a phenotype similar to human type 2 diabetes/obesity.[4] there are no studies in human subjects that causally relate clock genes to the development of T2DM, epidemiological data have shown that shift workers – who are known to experience disrupted circadian rhythms5 – are at increased risk of developing cardiometabolic disease.[6,7] Disruption of circadian rhythms in night shift workers is thought to result from misalignment between the central clock that tunes metabolism to sleep mode in the evening hours, and external stimuli associated with the requirements of work that force the night shift worker to remain in active.[8] Light, physical activity and stress hormones affect glucose metabolism directly and through the circadian clock in this group of workers. A metaanalysis of nine cross-sectional studies including almost 14,000 participants and four prospective studies with almost 9500 participants found a 57% higher incidence of the metabolic syndrome in workers exposed to night shift work as compared to workers who had never been exposed to night shift work.[10]
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