Study finds working night shift when young increases women’s breast cancer risk

Boston – Women who work the night shift as young adults may have an increased risk of breast cancer, according to a study of nurses conducted by the Channing Division of Network Medicine at Brigham and Women’s Hospital.

Researchers examined 24 years of data from more than 190,000 women enrolled in the Nurses’ Health Study and the Nurses’ Health Study II, with the latter populated by younger nurses. From these two groups, more than 9,500 received breast cancer diagnoses. Based on the nurses’ work histories, researchers discovered a two-fold increase in breast cancer risk among younger nurses who had more than 20 years of rotating night-shift work.

“We suspect that the increased risk among this younger population is reflective of the timing of the exposure to shift work, which was accrued primarily during younger ages, and that younger women may be more vulnerable to risk,” Dr. Eva Schernhammer, study co-author and associate epidemiologist at Brigham and Women’s Hospital, said in an Aug. 4 press release.

In the group with older nurses, those who performed 30 or more years of shift work had no increased risk of breast cancer when compared with nurses who never worked at night. The researchers emphasized that they followed up with this group mostly after the nurses had retired, suggesting that breast cancer risk can be reduced as shift work decreases.

The researchers say additional study is needed.

The study was published Aug. 3 in the American Journal of Epidemiology.