O004 Circadian and behavioural impacts on salivary cortisol during simulated nightshifts

Abstract Introduction Cortisol regulates multiple body systems and displays a distinct circadian rhythm. Nightshift disrupts this rhythm likely disturbing physiological processes regulated by cortisol. The cumulative effect of consecutive nightshifts, eating during nightshift, on cortisol is unclear. This study aimed to determine the impact four-consecutive simulated nightshifts with varied conditions at night salivary Methods N=52 healthy non-shift-working individuals (29-male, 23-female, 24.5±4.8-years; BMI 24.22±2.48 kg/m2) completed four-in-lab (N1-4 2000h-0530h). Participants were randomly assigned meal-at-night (n=17), snack-at-night (n=16), or no-food-at-night (n=19) conditions. Saliva was collected across 15-time-points between 2000h-0530h per-nightshift. Mixed-effects ANOVAs tested for fixed-effects night, time, condition, their interactions cortisol, area under curve, ground, increase (AUCg, AUCi), post-meal-snack diurnal-cortisol rise (0300h-0530h). Results Nightshifts produced significant effects time night*time (p<0.001), whereby levels 2000h increased 0530h decreased each nightshift. Post-food-intake revealed condition respectively (AUCg; p<0.001; AUCi; p<0.001) higher in meal snack vs. no-meal-condition. There night*time*condition (p=.029) greater decreases no-meal-conditions nightshift Discussion These results support that significantly alter daily rhythms. Such changes may exacerbate shift-work-related alterations influenced Further research needed better understand relationships altered sleep/wake cycles, meal-timing, cortisol-regulated health outcomes shift-workers.