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October 19, 2025 57 mins

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How artificial light impacts female menstrual cycles and their relationship to lunar cycles of the moon.

Summary: Dr. Förster talks about how biological clocks, including circadian, tidal, lunar, and annual cycles, regulate behaviors in various species, with a focus on lunar cycle effects on human menstrual cycles. They explore historical and modern data suggesting that menstrual cycles may synchronize with lunar phases, a phenomenon potentially disrupted by modern artificial lighting, particularly blue light from LEDs post-2010. The conversation also covers circadian rhythm mechanisms in fruit flies and humans, highlighting the role of light and neuropeptides in maintaining biological synchrony.

About guest: Charlotte Förster, PhD is a senior professor at the University of Würzburg specializing in chronobiology, particularly circadian rhythms in fruit flies, and has recently explored lunar cycle influences on human menstrual cycles.

Discussion Points:

  • Biological Clocks: Various clocks (circadian, tidal, lunar, annual) regulate behaviors; circadian clocks manage 24-hour cycles, while lunar clocks influence reproduction in marine species like corals and Christmas Island crabs.
  • Lunar Cycle & Menstruation: Historical data (pre-2010) showed many women’s menstrual cycles synchronized with lunar phases (full or new moon), but this decreased post-2010, possibly due to blue light from LEDs disrupting biological rhythms.
  • Blue Light Impact: Blue light from modern devices mimics daylight, potentially desynchronizing circadian and lunar clocks, with melanopsin in the eyes playing a key role in light sensitivity.
  • Winter Synchronization: Menstrual cycle synchrony with lunar phases is stronger in winter, particularly January, possibly due to brighter moonlight or gravitational effects when Earth is closest to the Sun.
  • Circadian Mechanisms: In fruit flies, 240 neurons manage circadian rhythms via clock genes with a 24-hour feedback loop, conserved in humans, where neuropeptides regulate slower, sustained rhythms.
  • Health Implications: Disrupted circadian rhythms can desynchronize body clocks, impacting digestion, immunity, and increasing risks of cardiovascular issues, obesity, and cancer.
  • Lifestyle Tips: To maintain synchrony, maximize daytime light exposure, minimize nighttime blue light, time meals appropriately, and exercise during the day, not late at night.

*Not medical advice.

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