Artificial Light Disrupts Natural Connection Between Menstrual Cycles and Lunar Phases, Study Finds

Recent research suggests that artificial lighting, particularly LED lights and screen exposure, significantly weakens the natural synchronization of women's menstrual cycles with lunar phases. The study, conducted by scientists from Julius-Maximilians-Universität Würzburg, analyzed menstrual data spanning the past fifty years. Prior to widespread LED use and smartphone prevalence, women's menstrual cycles closely aligned with the moon's cycle, which is approximately 29.5 days. However, since 2010, this alignment has diminished, with cycles only showing some synchronization during the month of January when lunar gravitational forces are at their strongest.

The researchers propose that humans possess an internal moon clock tuned to the lunar cycle through natural night light and gravitational effects. Yet, increased artificial nighttime illumination interferes with this biological rhythm. The interference is especially pronounced with LEDs, which emit high-energy blue light, to which our eye's photoreceptors are highly sensitive. This blue light’s intensity exceeds that of traditional lighting sources like gas lamps or incandescent bulbs.

Supporting evidence comes from sleep studies and psychiatric research. For instance, people tend to sleep less during full and new moon periods, and individuals with bipolar disorder may experience mood swings in tandem with lunar phases. Despite the existence of lunar-driven biological rhythms in marine life, the presence of a lunar clock in humans remains hypothetical. Nonetheless, the findings indicate that gravitational forces and moonlight may influence human physiology, and artificial light at night disrupts these potential natural connections.

The study also raises implications for fertility, as menstrual cycle length is considered an indicator of female reproductive health. Shortening of cycles due to artificial illumination potentially diminishes the likelihood of lunar synchronization. Overall, the results highlight the impact of modern lighting on biological rhythms and may have broader consequences for understanding human health and reproductive processes.

Source: https://medicalxpress.com/news/2025-09-artificial-weakens-menstrual-natural-synchronization.html