Effects of Light at Night on the Circadian System in Nurses

Details

• Personal Author:
  Hankinson S ; Laden F ; Lockley S ; Rea M ; Schernhammer E
• Description:
  Occupational safety and health issues that were addressed. Observational studies have consistently associated rotating shift work with increases in cancer risk, prompting the WHO in December 2007 to classify night shift work a probable carcinogen - the main operating mechanism being assumed circadian disruption by means of melatonin suppression (1). Still, while cancer is one of the bleakest disease endpoints, a broader range of outcomes is affected: increases in cardiovascular risk; peptic ulcer disease; chronic fatigue and various sleep problems; higher body weight due to abnormal eating habits and/or metabolism; a higher abortion and miscarriage rate as well as lower pregnancy rates; higher rates of substance abuse and depression; a greater number of vehicle accidents; and a higher divorce rate have been reported in shift workers. Further, chronic sleep deprivation leads to mistakes that also affect the health of others. Importance of the problem. Almost 15 million Americans regularly work alternate shifts, including evening (4.7 M), night (3.2 M), and rotating shifts (2.5 M) or other employer-arranged irregular schedules (2). Shift work is integral to the modern work force, which spans all age and ethnic groups. While fewer women than men work alternate shifts (12.4% vs. 16.7%), there is a substantially larger proportion of female night workers in health care and social assistance professions, including nursing. Approach. During the initial phase of this project, the Lighting Research Center at RPI (under the direction of Mark Rea) developed in a collaborative effort a Daysimeter, which was refined in three major steps until it was found acceptable by nurses. The Daysimeter represents an improvement compared to conventional lightmeters because its blue sensor is calibrated toward short-wavelength visual light and because it is head- mounted (rather than wrist-mounted) to avoid significant errors in weighting retinal flux. Further, the Daysimeter has an internal clock unlike any other conventional illuminance meter and can, therefore, characterize both the time and the duration of circadian light exposure. Applying this new device, together with 4-hourly urine collections over three days for melatonin measurements in a large scale prospective cohort study like the NHS2 is unprecedented in literature and vital for progress in light research. Overall, 148 women participating in NHS2 were recruited and successfully completed a 7-day light and urine collection scheme. Key Findings. 24-hour light exposure was lower among rotating-shift workers on night shift (NS) compared to day shift (DS) workers. Average light exposure over night was significantly higher at NS compared to DS and night workers off shift (OS). Compared to DS or OS, in NS, the amplitude of melatonin's primary urinary metabolite, aMT6, was significantly lower and its acrophase was delayed by one hour. Both intensity of light exposure overnight and activity index were significantly and inversely associated with aMT6 (P<0.01). Duration of light exposure above a certain lux threshold was also positively associated with melatonin levels, e.g., each hour exposed to more than 20 lux light was associated with 0.06 decrease in log-transformed aMT6. Next we found that, in multivariate analyses, chronotype was statistically significantly associated with aMT6 level (P < 0.001). We further observed that definite morning types were 2.7 hours phase advanced and had the highest melatonin amplitude compared to definite evening types (P trend < 0.001). Taking daytime naps was associated with lower overnight melatonin secretion. However, this association was not statistically significant after adjustment for possible cofounders. Late-night meal also was not independently associated with aMT6 level. Number of night shifts during the past 30 days and number of years having worked rotating shifts over the past 20 years were not statistically significantly associated with aMT6. We observed no statistically significant association between aMT6 and alcohol use, smoking, non-steroidal anti-inflammatories, beta-blockers, anti-depressants, and hormone therapy. Lastly, using the light measures obtained from the Daysimeter, we validated a newly developed paper-based questionnaire for self-reported light exposure (H-LEA). How the results can be utilized in the work place. The Daysimeter is a readily applicable instrument which has been tested in the field in ours as well as other applications since its initial conception. The H-LEA questionnaire is a practical and readily applicable method of assessing light exposure in large scale epidemiologic studies to study the effects of shift work on health. Our findings relating light to melatonin levels suggest that certain thresholds of light determine duration and intensity of light exposure needed to negatively affect the circadian system. Chronotype is an important factor which should be considered in future studies of shift workers and health. [Description provided by NIOSH]
• Subjects:
  Circadian Rhythm Health Personnel Lighting Occupational Health Safety Shift Work Schedule Sleep Sleep Initiation And Maintenance Disorders Women
• Keywords:
  Biological Rhythms Circadian Rhythms Health Care Workers Health Effects Hormone Activity Nurses Physical Exercise Shift Work Sleep Deprivation Work Schedules
• Series:
  Grant Final Reports
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Final Grant Report
• Place as Subject:
  Massachusetts ; OSHA Region 1
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  OEP - Office of Extramural Programs
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-31
• NIOSHTIC Number:
  nn:20059593
• NTIS Accession Number:
  PB2021-100157
• Citation:
  Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-008171, 2011 Jun; :1-31
• Contact Point Address:
  Eva Schernhammer, MD, DrPH, Brigham and Women's Hospital, Channing Laboratory, 181 Longwood Avenue, Boston, MA 02115
• Email:
  eva.schernhammer@channing.harvard.edu
• Federal Fiscal Year:
  2011
• NORA Priority Area:
  Healthcare and Social Assistance
• Performing Organization:
  Brigham and Women's Hospital
• Peer Reviewed:
  False
• Start Date:
  20050901
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20110228
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:cc0f7afe65c620bb6937f7c44115daf2737473e8f02a68b1676bdc4797c7ea23c6c2fad8275005c018ed13822beb92e68ad7ffa76bd66b6991048d1a19bc7ddf
• Download URL:
  https://stacks.cdc.gov/view/cdc/218982/cdc_218982_DS1.pdf
• File Type:
  [PDF - 1.31 MB ]