Night shift work is tied to breast cancer

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A new study identifies a link between night shift work and risk of breast cancer, according to Canadian researchers.

In an investigation of 1,100 women with breast cancer and more than 1,100 without it, Queen's Cancer Research Institute researchers found that those who had worked for more than 30 years on a night shift had a higher rate of breast cancer. The institute is part of Queen's University in Ontario. 

One-third of the women in each group worked on the night shift. Subjects were generally in their mid-to-late 50s.

Possible explanations for the link may be that night-shift workers have disruptions to their circadian rhythms, decreased melatonin levels, lower Vitamin D levels or more sleep disturbance problems, according to author Kristan J. Aronson, Ph.D.

Previous investigations also have found a link between night shift work and breast cancer. A 2012 Danish study indicated frequent night shift work increased the risk of breast cancer, while a 2011 study concluded breast cancer among Norwegian nurses may be related to consecutive night shifts.

The Canadian study appeared in Occupational and Environmental Medicine