Night Work May Increase Breast Cancer Risk

Researchers from Harvard University and Brigham and Women's Hospital have shown that working regular night shifts increases the risk of developing breast cancer by as much as 50 percent. The data is reported in the European Journal of Cancer.

The researchers analyzed data from more than 10,000 women and found that those who worked at night were one and a half times more likely to develop breast cancer than the daytime staff. Furthermore, the risk seemed to be associated with the amount of nighttime work performed. More night work was found to be associated with a higher risk of breast cancer.

One theory for the increased risk is that exposure to artificial light at night leads to an increased production of estrogen. Another theory is that the hormone melatonin plays a role. Melatonin is normally released in the body at night and helps regulate sleep patterns. Women with high levels of melatonin in the morning are at lower risk of breast cancer. When normal melatonin cycles are interrupted, production of estrogen is increased. Elevated estrogen levels can induce hormone-sensitive tumors in the breast.

Previous studies have demonstrated other health risks associated with night work. These other health risks include higher rates of heart disease, depression, and other types of cancer.