Women who work night shifts may have an increased risk for irregular periods and hormonal imbalances, according to a study being presented Monday at ENDO 2025, the Endocrine Society’s annual meeting in San Francisco, Calif. 

“Shiftwork-like light exposure disrupts the body’s internal timing, causing a split response where some females have disrupted reproductive cycles and hormones while others do not, but both groups face increased risk of ovarian disruption and pregnancy complications, including difficult labor, in response to shift work-like light exposure,” said Alexandra Yaw, Ph.D., a postdoctoral fellow in the Department of Animal Science at Michigan State University in East Lansing, Mich.

Yaw and colleagues used a mouse model of rotating light shifts that mimics changing light patterns to understand how shift work affects the reproductive system. Specifically, the researchers started and delayed the 12-hour light to 12-hour dark cycle for 6 hours every 4 days for 5 to 9 weeks.