Menstrual & Lunar Cycle Synchrony, Circadian Rhythms | Charlotte Förster

Mind & Matter

Menstrual & Lunar Cycle Synchrony, Circadian Rhythms | Charlotte Förster | 259

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Menstrual & Lunar Cycle Synchrony, Circadian Rhythms | Charlotte Förster | 259

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

Nick Jikomes

Oct 12, 2025

∙ Paid

Wide release date: October 20, 2025.

Episode 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 the 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. She holds a position at the Chair of Neurobiology and Genetics and is now retired but continues research as a senior professor.

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.

Reference paper:

Study: Synchronization of women’s menstruation with the Moon has decreased but remains detectable when gravitational pull is strong

Related content:

M&M 124 | Hormonal Contraception, Sex Hormones, Menstruation, Pregnancy, Puberty, Estrogens, Androgens, Effects of Birth Control on Cognition | Adriene Beltz

*Not medical advice.