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Working Graveyard Shift Doubles a Woman’s Breast Cancer Risk

Jul. 8, 2013|611 views
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A new study has concluded that working nightshift longterm dramatically increases a woman’s risk of developing breast cancer. The increase only emerges after 30 or more years, though. Experts have noted a link between nightshift work and increased risk of cancer before, but some have questioned the link. The present study, published online in Occupational and Environmental Health, shows that working nights eventually doubles a woman’s risk of breast cancer. Previous studies have focused on nurses, but the present study included women from a broad range of occupations. The new research demonstrates that it’s not just nightshift nurses who experience higher rates of breast cancer.

Experts theorize that the link between breast cancer and shift work may be due to nightly interruptions in the release of the sleep-inducing hormone, melatonin. Melatonin is produced primarily by the pineal gland (the “third eye”) in response to absolute darkness. It is an important regulator of the 24-hour cycle, or circadian rhythm, which determines a wide range of biological functions. Melatonin is also an extremely important natural antioxidant, credited with effecting or enabling repairs throughout the body while we sleep.

Some experts believe that disruptions in melatonin production may interfere with the body’s ability to destroy cells that might become cancerous. The authors of the present study note, though, that other mechanisms may explain the link between cancer risk and night shift work, including sleep disturbances, upset body rhythms, low vitamin D, or lifestyle differences. 

Grundy A, Richardson H, Burstyn I, Lohrisch C, SenGupta SK, Lai AS, et al. Increased risk of breast cancer associated with long-term shift work in Canada. Occupational and Environmental Medicine, 2013; DOI: 10.1136/oemed-2013-101482

Haus EL, Smolensky MH.Shift work and cancer risk: Potential mechanistic roles of circadian disruption, light at night, and sleep deprivation. Sleep Med Rev. 2013 Aug;17(4):273-84. doi: 10.1016/j.smrv.2012.08.003. Epub 2012 Nov 6.


Liu R, Fu A, Hoffman AE, Zheng T, Zhu Y. Melatonin enhances DNA repair capacity possibly by affecting genes involved in DNA damage responsive pathways. BMC Cell Biol. 2013 Jan 7;14:1. doi: 10.1186/1471-2121-14-1


Tags:  cancer risks