Twenty-four-hour light exposure and melatonin levels among shift workers

J Occup Environ Med. 2005 Dec;47(12):1268-75. doi: 10.1097/01.jom.0000184855.87223.77.


Objectives: We sought to measure melatonin levels and 24-hour light intensity exposure in health care workers over a 7-day period in natural occupational and residential settings.

Methods: Five office workers and 17 nurses working either days or rotating night and day shifts wore a device to record light intensity exposure for one or two 7-day periods, completed a questionnaire, and provided three saliva samples for melatonin.

Results: Rotating shift workers had irregular light exposure patterns and abnormal melatonin levels compared with those working days. In addition to lower-than-normal melatonin levels during sleep periods, rotating shift workers exhibited higher-than-normal melatonin levels on arising and during work. Self-reported years of shift work were correlated with measured melatonin and light.

Conclusions: Rotating shift work is supported as a surrogate for exposure to light-at-night and circadian disruption.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Female
  • Health Personnel
  • Humans
  • Light*
  • Male
  • Melatonin / analysis*
  • Middle Aged
  • Occupational Exposure*
  • Saliva / chemistry
  • Time Factors


  • Melatonin