ENDO 2025: Night Shifts Disrupt Women’s Hormonal System

Women who work night shifts are more likely to experience menstrual cycle irregularities and hormonal system disruptions. This conclusion comes from researchers at the University of Michigan, who presented their findings at the Endocrine Society’s ENDO 2025 meeting in San Francisco.

In a mouse experiment, scientists simulated a shift-work schedule by shifting the light cycle forward by six hours every four days. Within just a few weeks, half of the female mice developed irregular menstrual cycles, while tests showed hormonal imbalances and deteriorating ovarian health.

Analysis revealed that even in mice with preserved cycles, uterine and ovarian activity patterns were disrupted. All animals were able to conceive, but the experimental group had lower fertility rates and more frequent complications during delivery.

“Light exposure at night negatively affects the body’s internal clock. In some individuals this immediately causes hormonal disruptions, while in others it doesn’t. But in the long run, everyone is at risk of ovarian dysfunction and pregnancy complications, including difficult labor,” explained Alexandra Yau, research fellow at the University of Michigan.

In the future, the researchers plan to investigate how circadian rhythm disturbances specifically affect uterine function during pregnancy. According to the team, the new findings could help doctors warn patients about the risks of night-shift work and guide employers in developing more balanced schedules.