Shift Work, Chronotype, and Melatonin Rhythm in Nurses (NHS II Sub‑study)
Summary
This analysis of 130 nurses in the Nurses’ Health Study II tested how shift schedules and chronotype interact to affect melatonin rhythms. Compared to day-shift nurses, rotating-shift workers on nights had greater nighttime light exposure, lower overall melatonin levels, smaller peaks, and later timing of melatonin release. Chronotype also mattered: evening types had later peaks, while morning types had earlier, stronger peaks. Importantly, the effects of shift work and chronotype combined — when work schedules aligned poorly with chronotype, melatonin disruption was more pronounced.
Why It Matters For Night Shift Workers and Night Owls
This study shows that both your work schedule and your natural body clock shape how much circadian disruption you experience. Nurses working nights had reduced and delayed melatonin signals — a key hormone that regulates sleep and recovery. Evening types coped a bit better with night work, while morning types showed stronger misalignment. For shift workers, this suggests that knowing your chronotype and adjusting light exposure, sleep timing, and shift patterns where possible could help protect circadian rhythms and improve rest.
Notes
Nurses’ Health Study II sub‑study.