Eating during the biological night is associated with nausea

Objectives: This study assessed whether there was a time-of-day effect on nausea reports in participants during studies employing circadian protocols. 

Methods: Visual-analog-scales of nausea ratings were recorded from 34 participants (18-70 years; 18 women) during forced desynchrony studies, where meals were scheduled at different circadian phases. Subjective nausea reports from a further 81 participants (18-35 years; 36 women) were recorded during constant routine studies, where they ate identical isocaloric hourly snacks for 36-40 hours. 

Results: Feelings of nausea varied by circadian phase in the forced desynchrony studies, peaking during the biological night. Nausea during the constant routine was reported by 27% of participants, commencing 2.9 ± 5.2 hours after the midpoint of usual sleep timing, but was never reported to start in the evening (4-9 PM). 

Conclusions: Nausea occurred more often during the biological night and early morning hours. This timing is relevant to overnight and early morning shift workers and suggests that a strategy to counteract that is to pay careful attention to meal timing.