Shift Work and Breast Cancer.

Sarah Gehlert,Mark Clanton

doi:10.3390/ijerph17249544

Abstract

The rates of shift work outside of daylight hours have increased in recent years, and nighttime shift work is now considered a potential carcinogenic occupational exposure. Light at night exposure, lower melatonin production, and the production of stress-related mediators disrupt normal sleep–wake cycles. Women who work lower-wage jobs and part-time workers whose shifts are determined entirely by their supervisors (rotating shifts) may be subject to stress related to efforts to align childcare and other needs with the unpredictable nature of rotating shift work. The causal link between breast cancer and the sleep cycle or circadian disruption are yet to be established; however, disruption of the circadian cycles by light at night exposure or chronic exposure to stress-related mediators have all been linked to the increased risk of breast cancer. We review the existing literature on shift work and breast cancer, identify knowledge gaps, and suggest future directions for research.

Highlights

Rates of shift work outside of daylight hours have increased in recent years, and nighttime shift work is considered a potential carcinogenic occupational exposure as a result of decreased melatonin levels caused by light at night exposure [1,2]
While many authors have posited a link between shift work and breast cancer and a separate body of investigation has looked at the psychological, behavioral, and broad health effects of shift work on women, the two bodies of research have failed to overlap over three decades of inquiry
Numerous epidemiological studies have suggested that night shift work may increase breast cancer risk, few of these largely observational studies have clearly documented the necessary disruption of the circadian rhythm that is required by the International Agency for Cancer Research designation of shift work as a category 2a carcinogen

Summary

Introduction

Rates of shift work outside of daylight hours have increased in recent years, and nighttime shift work is considered a potential carcinogenic occupational exposure as a result of decreased melatonin levels caused by light at night exposure [1,2]. While many authors have posited a link between shift work and breast cancer and a separate body of investigation has looked at the psychological, behavioral, and broad health effects of shift work on women, the two bodies of research have failed to overlap over three decades of inquiry. Another important consideration is that breast cancer mortality is much higher among underrepresented minority and lower socioeconomic status women globally; women who are less likely to control the timing of their shifts. We do this by reviewing literature on shift work and breast cancer, the psychosocial effects of shift work, and the differential effects of socioeconomic status on the outcomes of shift work

State of the Literature

Epidemiology

Low Wage Shift Workers and Breast Cancer

Future Directions for Research

Findings

Conclusions