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Shift Work Has Little Impact on Breast Cancer Risk: Study

Shift Work Has Little Impact on Breast Cancer Risk: Study

(Copyright Fotolia)

By    |   Thursday, 06 October 2016 11:46 AM

Although an earlier study found that night shift work probably increased the risk of breast cancer, three new studies and a review of current evidence found that working at night has little or no effect on breast cancer risk.

In 2007, a review by the World Health Organization's International Agency for Research on Cancer stated that shift work that disrupts the circadian rhythm — the internal "body clock" — was a possible carcinogen.


Their findings were based on evidence about breast cancer in animal studies. At the time there was only limited evidence about breast cancer risk in humans.


Researchers from the Cancer Epidemiology Unit at Oxford University, United Kingdom, followed a total 800,000 women in three large U.K. studies to determine whether night shift work could influence breast cancer risk.


Participants answered questions on whether or not they did shift work and were then followed to determine which women developed cancer. The researchers found no increase in breast cancer risk associated with night shift work, including long-term night shifts.


In a meta-analysis of the worldwide evidence, the authors combined results from the three U.K. studies with those from all seven previously published prospective studies (two in the U.S., two in China, two in Sweden, and one in the Netherlands).


The 10 studies included a total of 1.4 million women among whom 4,660 breast cancers occurred in women who reported ever having done night shift work.


"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 3 new UK studies or when we combined results from all 10 studies that had published relevant data," said researcher Ruth Travis.


Compared with women who did no night shift work, the combined relative risks taking all 10 studies together were 0.99 for any night shift work, 1.01 for 20 or more years of night shift work, and 1.00 for 30 or more years night shift work. In other words, the incidence of breast cancer was essentially the same whether someone did no night shift work at all or did night shift work for several decades.


The study was published in the Journal of the National Cancer Institute.


The study is good news for the millions of American women who work at night, although a study published earlier this year in JAMA found that working night shifts and the risk of heart disease.


Women who worked rotating night shifts for more than 10 years increased their risk of heart disease 15 to 18 percent.


About 12 percent of American women will develop breast cancer during their lifetime. In 2016, 246,000 new cases of invasive cancer are projected to be diagnosed, along with 61,000 new cases of non-invasive (in situ) breast cancer.

 

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Although an earlier study found that night shift work probably increased the risk of breast cancer, three new studies and a review of current evidence found that working at night has little or no effect on breast cancer risk. In 2007, a review by the World Health...
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2016-46-06
Thursday, 06 October 2016 11:46 AM
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