Shift work, chronotype, and melatonin rhythm in nurses

Pedram Razavi, Elizabeth E. Devore, Archna Bajaj, Steven W. Lockley, Mariana G. Figueiro, Vincent Ricchiuti, W. James Gauderman, Susan E. Hankinson, Walter C. Willett, Eva S. Schernhammer

Research output: Contribution to journalArticlepeer-review

90 Scopus citations


Background: Previous studies associated night-shift work with melatonin disruption, with mixed evidence regarding the modulating effects of chronotype (i.e., diurnal preference). Methods: One hundred and thirty active nurses (84 rotating-shift and 46 day-shift workers) in the Nurses' Health Study II wore a head-mounted light meter and collected spontaneous urine voids over 3 days. 6-Sulfatoxymelatonin (aMT6s), the major urinary metabolite of melatonin, was assessed. Results: Rotating-shift workers on night shifts had more light exposure and lower urinary melatonin levels during the night, and urinary melatonin rhythms with smaller peaks [11.81 ng/mg-creatinine/h, 95% confidence interval (CI), 9.49–14.71 vs. 14.83 ng/mg-creatinine/h, 95% CI, 11.72–18.75] and later peak onset (5.71 hours, 95% CI, 4.76–6.85 vs. 4.10 hours, 95% CI, 3.37–4.99), compared with day-shift workers. Furthermore, evening chronotypes' melatonin rhythms had later peak onset compared with morning types (4.90 hours, 95% CI, 3.94–6.09 vs. 3.64 hours, 95% CI, 2.99–4.43). However, among day-shift workers, morning chronotypes had melatonin rhythms with greater mean levels, larger peaks, and earlier peak onset compared with evening chronotypes; patterns were similar comparing evening versus morning chronotypes among rotating-shift workers on night shifts. The interaction of rotating-shift work and chronotype was significant across all parameters (P < 0.05). Conclusions: As expected, rotating-shift workers on night shifts had greater light exposure and lower urinary melatonin levels during the night compared with day-shift workers. Intriguingly, melatonin rhythms were dependent on both chronotype and rotating-shift work type, and better alignment of rotating-shift work and chronotype appeared to produce less disrupted melatonin rhythms. Impact: The joint effects of shift-work type and chronotype require attention in future studies.

Original languageEnglish
Pages (from-to)1177-1186
Number of pages10
JournalCancer Epidemiology Biomarkers and Prevention
Issue number7
StatePublished - 2019
Externally publishedYes


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