Working night shifts has little to no effect on breast cancer risk: Study

WASHINGTON, Oct. 6 (UPI) -- Women face little to no risk of developing breast cancer as a result of working night shifts, new research from Cancer Research UK suggests.

The new findings are based on a combination of data compiled by the Million Women Study, EPIC-Oxford, and UK Biobank. Approximately 1.4 million women were studied in 10 separate reports. Researchers compared women who had never worked night shifts to those who had, and found their occupational choices had no effect on their risk for developing breast cancer.

"We found that women who had worked night shifts, including long-term night shifts, were not more likely to develop breast cancer, either in the three new UK studies or when we combined results from all 10 studies that had published relevant data," lead author Dr. Ruth Travis explained in a press release.

The study, published in the Journal of the National Cancer Institute, refuted earlier research conducted by the International Agency for Research on Cancer in 2007. Scientists at the time claimed disrupting a woman's natural "body clock" with nighttime work was a probable cause of cancer.

When the results from all 10 studies were combined, researchers found the risk of developing breast cancer remained the same for women who never worked a night shift before and women who have been doing so for decades.

"The work demonstrates the power of very large, well-designed studies to answer important questions where previous evidence has been unclear," UK Biobank chief scientist Cathie Sudlow said.