How Modern Life Disrupts Women's Circadian Rhythms and Reproductive Health

A new study has uncovered how modern life disrupts the delicate balance between circadian rhythms and women's reproductive health. Led by Assoc. Prof. Jihwan Myung, the research shows that artificial light, irregular work schedules, and mood-stabilising drugs like lithium can interfere with menstrual cycles and worsen mental health conditions such as depression and bipolar disorder. The findings were published in Chronobiology in Medicine in June 2025.

The brain's master clock in the hypothalamus does more than regulate daily rhythms—it also interacts with reproductive systems that follow monthly cycles. This connection explains why seasonal changes affect menstrual timing: shorter daylight in winter tends to lengthen cycles, while longer summer days shorten them. But modern disruptions, from shift work to jet lag, throw these natural patterns off balance.

Women working night or rotating shifts face higher risks of irregular cycles, shorter luteal phases, and mood disorders. Meta-analyses from 2015 to 2023 found that nurses on such schedules experienced two to three times more menstrual disruptions than those on fixed daytime hours. Fixed routines, by contrast, help maintain hormonal stability and reduce psychological risks. The study also examined lithium, a common treatment for bipolar disorder. The drug was shown to lengthen circadian rhythms and disturb hormonal cycles, potentially contributing to menstrual irregularities. By combining human and animal data, the research highlights how mood medications can disrupt biological timing, worsening both reproductive and mental health. Millions of women already struggle with cycle disruptions linked to sleep patterns, work demands, and medication. The findings call for better treatment models that account for these overlapping rhythms, aiming to protect hormonal health while managing mood disorders.

The research underscores a critical link between mental and reproductive well-being. It suggests that future therapies could be tailored to individual circadian and hormonal rhythms, reducing side effects for women with mood disorders. Personalised, rhythm-informed approaches may soon offer a way to safeguard both mental and reproductive health.