Timed physical exercise does not influence circadian rhythms and glucose tolerance in rotating night shift workers: The EuRhythDia study

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.