How Night Shifts Breast Cancer Risks

Breast cancer risks higher after years of night shift

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Working at night causes changes in the body that can be harmful. In fact, the International Agency for Research on Cancer (IARC) classified night work as a "probable human carcinogen" in 2011.

A new study has found that women who have worked night shifts for 30 or more years have twice the risk of developing breast cancer as women who haven’t worked at night.

These findings took into account other risk factors and applied only to a relatively small number of women.

"Get 7 to 8 hours of sleep each night."

Anne Grundy, PhD, of the Department of Public Health Sciences at Queen’s University in Kingston, Ontario, Canada, led this international research study.

Dr. Grundy and colleagues were looking at the influence night shift work had on breast cancer risks among 1,134 women with breast cancer and 1,179 women of the same age without the disease.

Previous research has suggested that nurses who worked at night were at higher risk of breast cancer.

Between 2005 and 2010, the women completed questionnaires about their lifetime work history, reproductive and family histories and lifestyle issues.

These women had been engaged in a variety of occupations, and about a third of the participants had worked at night at some point in their lives.

Breast cancer risks were not affected among women who are worked at night for less than 30 years.

However, participants who were involved in nightshift work for 30 or more years had more than double the risk of developing breast cancer compared to women who had not worked at night.

The link was present regardless of other factors, including ethnicity, family history, pregnancies, breastfeeding history, age at the time of first mammogram, alcohol consumption, BMI (body mass index — a measure of body fat), menopausal status, education or income.

"Long-term night shift work in a diverse mix of occupations is associated with increased breast cancer risk and not limited to nurses, as in most previous studies," the authors wrote.
The researchers suggested that the association may be related to sleep disturbances, vitamin D levels, melatonin (hormone that helps regulate sleep) or lifestyle differences.

"Women who have been working nighttime shifts for many years should work closely with their physicians in being up-to-date with their breast cancer screenings," Adam Brufsky, MD, professor of medicine at the University of Pittsburgh School of Medicine, told dailyRx News.

"Maintaining a healthy diet and regular exercise may also assist in lowering the risk of breast cancer for these women," said Dr. Brufsky, who was not involved in this study.
This research was published in the July 1 issue of the BMJ.
The Canadian Institutes of Health Research funded the research. No conflicts of interest were disclosed.

Reviewed by: 
Review Date: 
July 1, 2013
Last Updated:
July 31, 2013