Glucose tolerance in mice exposed to light-dark stimulus patterns mirroring dayshift and rotating shift schedules.

Glucose tolerance was measured in (nocturnal) mice exposed to light-dark stimulus patterns simulating those that (diurnal) humans would experience while working dayshift (DSS) and 2 rotating night shift patterns (1 rotating night shift per week [RSS1] and 3 rotating night shifts per week [RSS3]). Oral glucose tolerance tests were administered at the same time and light phase during the third week of each experimental session. In contrast to the RSS1 and RSS3 conditions, glucose levels reduced more quickly for the DSS condition. Glucose area-under-the-curve measured for the DSS condition was also significantly less than that for the RSS1 and RSS3 conditions. Circadian disruption for the 3 light-dark patterns was quantified using phasor magnitude based on the 24-h light-dark patterns and their associated activity-rest patterns. Circadian disruption for mice in the DSS condition was significantly less than that for the RSS1 and RSS3 conditions. This study extends previous studies showing that even 1 night of shift work decreases glucose tolerance and that circadian disruption is linked to glucose tolerance in mice.

Circadian Disruption: comparing humans with mice.

Disruption of the 24-h light-dark cycle has been implicated as an endocrine disruptor and linked to increased morbidity and mortality in animal studies. Previously reported measurements of circadian disruption in day-shift and rotating-shift nurses were compared with new mouse data where the light-dark patterns simulated shiftwork. Phasor magnitudes, a measure of circadian entrainment, were shown to be similar for humans and for mice when exposed to similar patterns of light and dark. Phasor analyses may be a useful method for quantitatively bridging ecological measurements of circadian disruption in human with parametric studies of health outcomes in a mouse model.