The association between different night shiftwork factors and breast cancer: a case–control study

• Published in: British journal of cancer Vol. 109; no. 9; pp. 2472 - 2480
• Main Authors: Fritschi, L, Erren, T C, Glass, D C, Girschik, J, Thomson, A K, Saunders, C, Boyle, T, El-Zaemey, S, Rogers, P, Peters, S, Slevin, T, D'Orsogna, A, de Vocht, F, Vermeulen, R, Heyworth, J S
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29.10.2013; Nature Publishing Group
• Subjects: 692/699/67/1347; 692/699/67/2324; Adult; Aged; Aged, 80 and over; Alcohol; Alcohol use; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Breast cancer; Breast Neoplasms - epidemiology; Breast Neoplasms - etiology; Cancer Research; Carcinogens; Case-Control Studies; Cell division; Circadian rhythm; Drug Resistance; Epidemiology; Exercise; Female; Gynecology. Andrology. Obstetrics; Humans; Life Style; Lifestyles; Mammary gland diseases; Medical research; Medical sciences; Melatonin; Middle Aged; Molecular Medicine; Multiple tumors. Solid tumors. Tumors in childhood (general aspects); Oncology; Population; Risk; Risk Factors; Shift work; Sleep; Surveys and Questionnaires; Tumors; Western Australia - epidemiology; Work Schedule Tolerance; Working groups; Young Adult; Western Australia; Australia; Western Australia Australia; Australia, Western Australia; shiftwork; breast cancer; case–control; Mammary gland diseases; Breast disease; Association; Cancerology; Night; Breast cancer; Malignant tumor; Case control study; case―control; Cancer
• ISSN: 0007-0920; 1532-1827
• DOI: 10.1038/bjc.2013.544

Background: Research on the possible association between shiftwork and breast cancer is complicated because there are many different shiftwork factors, which might be involved including: light at night, phase shift, sleep disruption and changes in lifestyle factors while on shiftwork (diet, physical activity, alcohol intake and low sun exposure). Methods: We conducted a population-based case–control study in Western Australia from 2009 to 2011 with 1205 incident breast cancer cases and 1789 frequency age-matched controls. A self-administered questionnaire was used to collect demographic, reproductive, and lifestyle factors and lifetime occupational history and a telephone interview was used to obtain further details about the shiftwork factors listed above. Results: A small increase in risk was suggested for those ever doing the graveyard shift (work between midnight and 0500 hours) and breast cancer (odds ratio (OR)=1.16, 95% confidence interval (CI)=0.97–1.39). For phase shift, we found a 22% increase in breast cancer risk (OR=1.22, 95% CI=1.01–1.47) with a statistically significant dose–response relationship ( P =0.04). For the other shiftwork factors, risks were marginally elevated and not statistically significant. Conclusion: We found some evidence that some of the factors involved in shiftwork may be associated with breast cancer but the ORs were low and there were inconsistencies in duration and dose–response relationships.