Businesswoman in her office at night working late

(© Halfpoint -

ISTANBUL, Turkey — A new study warns that just four weeks of shift work could disrupt women’s biological clocks and negatively impact their fertility. Study authors say shift work can interfere with the body’s circadian rhythm, which is the physical, mental, and behavioral changes that follow a 24-hour cycle in response to light variations.

These internal clocks regulate numerous biological functions and processes, such as the sleep cycle, digestion, hormone flow, and reproduction. However, they can be easily disrupted by inappropriate light exposure, such as exposure to light at night.

The body’s primary biological clock is located in a small region in the center of the brain known as the hypothalamus. This area plays a crucial role in reproductive function by acting on the pituitary gland, which is attached to the base of the hypothalamus, to regulate ovarian activity and promote ovulation.

The study replicated long-term shift work conditions in female mice by continuously altering their light-dark cycle. Over four weeks, researchers advanced and delayed light exposure by 10 hours. They discovered that this disruption eliminated the substantial release of the luteinizing hormone from the pituitary gland, which typically triggers ovulation, subsequently reducing fertility.

“The decreased fertility is due to an alteration of the master circadian clock signaling towards the hypothalamic reproductive circuit,” explains lead researcher Marine Simonneaux, a Ph.D. student from the University of Strasbourg, in a media release. “Specifically, our research shows that four weeks of chronic shift exposure impairs the transmission of light information from the master biological clock to the kisspeptin neurons, known to drive the timing of the pre-ovulatory luteinizing hormone surge.”

Woman wearing blue light glasses while doing work at night on computer
(© Maridav –

Past studies, conducted on both mice and humans, have indicated negative effects on female reproduction when the circadian rhythm is disrupted. The research team from the Institute of Cellular and Integrative Neurosciences (INCI) and the University of Strasbourg have previously demonstrated that shift work-like patterns over several weeks led to a decreased pregnancy rate in female mice.

Future research will investigate whether shift work-like patterns also alter other internal clocks.

“The circadian rhythm requires not only the proper functioning of the master biological clock but also the synchronized activity of numerous secondary clocks found in other brain areas and peripheral organs, including reproductive organs. Understanding the precise mechanisms by which circadian disruption alters reproductive function is important,” Simonneaux elaborates. “It may pave the way for potential preventive and therapeutic interventions to reduce some of the negative effects of shift work on women’s fertility.”

Researchers presented their findings at the 25th European Congress of Endocrinology (ECE) in Istanbul, Turkey.

South West News Service writer Alice Clifford contributed to this report.

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