Night-shift work and risk of colorectal cancer in the nurses' health study.
Exposure to light at night suppresses the physiologic production of melatonin, a hormone that has antiproliferative effects on intestinal cancers. Although observational studies have associated night-shift work with an increased risk of breast cancer, the effect of night-shift work on the risk of other cancers is not known. We prospectively examined the relationship between working rotating night shifts and the risk of colorectal cancers among female participants in the Nurses' Health Study. We documented 602 incident cases of colorectal cancer among 78 586 women who were followed up from 1988 through 1998. Compared with women who never worked rotating night shifts, women who worked 1-14 years or 15 years or more on rotating night shifts had multivariate relative risks of colorectal cancer of 1.00 (95% confidence interval [CI] = 0.84 to 1.19) and 1.35 (95% CI = 1.03 to 1.77), respectively (P(trend) =.04). These data suggest that working a rotating night shift at least three nights per month for 15 or more years may increase the risk of colorectal cancer in women.
Schernhammer
Eva S
ES
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA. schernhammer@channing.harvard.edu
Laden
Francine
F
Speizer
Frank E
FE
Willett
Walter C
WC
Hunter
David J
DJ
Kawachi
Ichiro
I
Fuchs
Charles S
CS
Colditz
Graham A
GA
D000328:Adult; D000368:Aged; D015982:Bias; D016022:Case-Control Studies; D015179:Colorectal Neoplasms / Q000097:blood / Q000209:etiology*; D005260:Female; D006306:Health Surveys; D006801:Humans; D008019:Life Style; D008550:Melatonin / Q000097:blood*; D008875:Middle Aged; D009726:Nurses / Q000706:statistics & numerical data*; D016017:Odds Ratio; D011446:Prospective Studies; D012107:Research Design; D018570:Risk Assessment; D012307:Risk Factors; D013997:Time Factors; D014481:United States / Q000453:epidemiology; D014940:Work Schedule Tolerance
D008550:Melatonin