Working the night shift may lead to breast cancer: study

Copenhagen – Women who work the night shift more than twice a week may have a higher risk of breast cancer, according to a study from the Danish Cancer Society.

Researchers collected data on more than 18,500 women who had worked for the Danish military between 1964 and 1999, according to the study abstract. They compared the work and lifestyle behaviors of 210 women with breast cancer and 900 women without it and found working at night increased the risk of breast cancer by 40 percent. The risk doubled for women who worked the night shift at least three times a week for six years or more.

The risk was even greater for women who described themselves as “morning” people. They were almost 4 times more likely to develop breast cancer than women who did not work nights, while self-described “evening” people had twice the risk, the study indicates.

Researchers recommended women limit night shift work to less than three times a week.

The study was published online May 28 in the journal Occupational & Environmental Medicine.