Minimizing Cancer Risk in Shift Workers

Details

• Personal Author:
  Hankinson S ; Rosner B ; 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. 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. 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. Because no definitive strategy currently exists to reduce the cancer risk associated with shift work-induced circadian disruption, determining what aspects of shift schedules are most detrimental to health is the next frontier in shift work and disease prevention. To date, no study has examined how specific aspects of shift schedules including length, frequency of rotation, and hours worked per week interact and relate to cancer risk. Moreover, whether there is an age range at which people are particularly vulnerable to the effects of circadian disruption also remains unclear. Future research would benefit from a clear and complete description of work schedules and their effects on human cancer risk. Approach. In 2009, we have added a battery of shift work questions to the main NHS2 questionnaire. We newly assess specific aspects of the nurses' work schedule including types of shift schedules and changes throughout their professional career. In addition, other factors of potential relevance to circadian disruption were assessed, including morningness-eveningness and sleep duration during each of the various life time periods. To evaluate the hypothesis that certain aspects of shift work schedules are more strongly associated with breast cancer risk than others, we will use both a cohort and cross-sectional study approach. We estimate 1,108 newly diagnosed cases of breast cancer between 2009 and 2013. We will use these cases, as well as prevalent cases to enhance the power of subanalyses, for an estimated total of 4,295 women with a diagnosis of breast cancer through 2013. Because mechanisms that link shift work to breast cancer risk are similar for other cancers, the findings from this proposal are likely to affect not only the risk of breast cancer but that of other cancers and men as well. We expect that the impact of our results will extend well beyond the specific aims we currently propose. Ultimately, as time progresses and nurses become older, this data and the newly added battery of shift work questions will lay the foundation for a comprehensive and unique study of shift work on the health needs of older workers. Key Findings. Over the past five years, our work using data from the Nurses' Health Study cohorts has produced landmark findings and generated provocative novel hypotheses related to the health effects of night work and sleep deprivation: We showed that night shift work increases the risk of a number of different cancers (most notably breast, but also colorectal, endometrial, and lung cancer), after extended periods of night work, and that risk appears to wane over time once night work stops. In addition, we have linked rotating night shift work . through its profound effects on metabolism and weight (i.e. obesity) to other major chronic diseases, including cardiovascular disease, metabolic syndrome, hypertension, stroke, endometriosis, and type 2 diabetes; we found effect variation by ethnicity, and we developed melatonin as a biomarker for the circadian system, which we subsequently linked to cancer and other chronic disease risk (e.g., diabetes, hypertension). We showed that these effects are mediated by variants in clock genes [women homozygous for the minor allele (AA) in the circadian gene NPAS2 Ala394Thr, with . 24 months of shift-work having a 2.83- times higher breast cancer risk compared to homozygous AA women with < 24 months of shift-work (95% CI = 1.47-5.56)] and a variety of biomarkers including melatonin. We studied the precise associations between light exposure and the circadian system, delineating that, and how, consecutive number of night shifts matters, and how chronotype mitigates these effects. Lastly, we have established that shift work can affect reproduction, demonstrating menstrual cycle changes and higher spontaneous abortion rates in night shift workers. How the results can be utilized in the work place. This project's results will not have any direct impact on the NHS2 cohort, but the findings may benefit women who work rotating night shifts in the future. Ultimately, as outlined in detail in our proposal, they are geared towards providing a frame work for health policy makers on which they may chose to base decisions to change shift work schedules in order to minimize breast cancer risk in night workers. 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:
  Biomarkers Circadian Rhythm Cohort Studies Health Personnel Neoplasms Occupational Health Safety Sleep Sleep Initiation And Maintenance Disorders Surveys And Questionnaires Urogenital System

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• Keywords:
  Breast Cancer Cancer Rates Circadian Rhythms Cohort Studies Cross Sectional Studies Health Effects Nurses Nursing Questionnaires Reproductive Effects Shift Workers Sleep Deprivation Work Schedules

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• 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:
  1-15
• NIOSHTIC Number:
  nn:20053820
• NTIS Accession Number:
  PB2019-100391
• 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-009803, 2015 Nov; :1-15
• Contact Point Address:
  Eva Schernhammer, MD, DrPH, Professor of Epidemiology, Lecturer of Medicine, Harvard Medical School, Harvard School of Public Health, Brigham and Women's Hospital, Channing Laboratory, 181 Longwood Avenue, Boston, MA 02115
• Email:
  eva.schernhammer@channing.harvard.edu
• CAS Registry Number:
  Melatonin (CAS RN 73-31-4)
• Federal Fiscal Year:
  2016
• NORA Priority Area:
  Healthcare and Social Assistance
• Performing Organization:
  Brigham and Women's Hospital, Inc., Boston, Massachusetts
• Peer Reviewed:
  False
• Start Date:
  20100801
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20190831
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:8edcadd2cbc2eb8a8209d8352c57ae82997b79360d24087075acd22e80383c185e19ee8bc9a31a5f25cd190b35134dd75773037f04bc2f91ea1b2ab9a0ac8ae4
• Download URL:
  https://stacks.cdc.gov/view/cdc/218783/cdc_218783_DS1.pdf
• File Type:
  [PDF - 232.75 KB ]