The Moon’s Phases, LED Light, and the Menstrual Cycle – How Light Shapes Hormones and Rhythms
Have you ever noticed your period aligning with the full moon, or heard that women who spend a lot of time together can synchronize their cycles? The idea that menstrual cycles are linked to the moon’s phases is both ancient and fascinating. In modern times, however, a new factor has entered the picture: artificial light—especially the bluish glow of LEDs from screens and lamps that illuminate our nights.
Could this modern light environment disrupt women’s hormonal rhythms and their potential synchronization with the moon—or with each other? Let’s explore what science says about the relationship between lunar phases, melatonin, light exposure, and reproductive hormones.
Historical Observations: Menstruation and the Moon
The moon’s cycle (about 29.5 days) closely resembles the average menstrual cycle (around 28–29 days)—a coincidence too striking to ignore. Historically, stories have described women menstruating with either the new or the full moon.
Throughout the 20th century, several small studies suggested that many women’s cycles seemed to follow the lunar rhythm. However, more recent large-scale analyses—using data from hundreds of thousands of women through health apps—have found no consistent connection. These datasets indicate that menstrual-moon synchronization is likely coincidental.
Interestingly, some newer studies suggest that the link may once have existed but weakened after 2010. Researchers suspect this could be due to increased exposure to artificial light—particularly LED lighting and screens emitting blue light that disrupt the body’s natural night rhythm.
The Biology of Light and Hormonal Rhythms
Melatonin, often called the “darkness hormone,” is produced by the pineal gland when it gets dark. It signals the body that it’s nighttime and helps regulate both sleep and hormonal balance. Exposure to light—especially blue light—suppresses melatonin and delays the natural circadian rhythm.
Melatonin also influences reproductive hormones through the hypothalamic-pituitary-ovarian axis. In animals, it controls seasonal breeding cycles, and in humans, studies show that light exposure can affect ovulation patterns.
In earlier experiments, researchers found that women with irregular cycles could achieve more stable menstrual patterns when exposed to dim light on specific nights—a practice sometimes referred to as “lunaception.” The light likely stimulated ovulation by slightly reducing melatonin at the right time.
These findings highlight that both natural and artificial light can affect hormonal rhythms more deeply than previously thought.
The LED Era: Impact on Menstrual Rhythms
Since 2010, LEDs and smartphones have transformed our light environment. LED light contains a higher proportion of blue wavelengths, which strongly suppresses melatonin and disrupts circadian timing.
Before artificial lighting, the full moon was the brightest source of night light. Today, the contrast between full and new moon has essentially disappeared under streetlights, screens, and indoor lighting. As a result, our bodies rarely experience true darkness.
This constant exposure to light may be one reason biological links between the moon and women’s cycles have weakened. A recent German study found that menstrual synchronization with the moon has dropped sharply since the widespread adoption of LED light. At the same time, strong light exposure itself appears to influence cycle length—possibly by stimulating hormones related to ovulation.
Similar effects are seen in women who work night shifts, where irregular light exposure often leads to irregular cycles and hormonal imbalances. Research in both humans and animals shows that disrupted circadian rhythms negatively affect fertility, hormonal balance, and sleep quality.
Biohacking Hormonal Rhythms
For those looking to optimize hormonal health, the goal is to reconnect with natural light and dark cycles. Here are some practical biohacks:
Morning light: Get bright natural light exposure first thing in the morning to stabilize your internal clock.
Dark nights: Dim your lights, use blackout curtains, and avoid bright lighting after sunset.
Reduce blue light: Use warm-white lighting or blue-light-blocking glasses in the evening.
Try dim lighting: Candlelight or soft red light at night helps signal your body that it’s time to rest.
Screen-free hour: Avoid phones and screens for at least an hour before bed to allow melatonin to rise naturally.
This isn’t just about improving sleep—it’s about restoring the deep connection between light, hormones, and reproductive balance. Our biology is still wired to follow the rhythms of the moon and the sun, even if modern technology has tried to pull us away from them.
While today’s science doesn’t conclusively support that women “sync with the moon,” there is strong evidence that our light environment profoundly affects hormonal health. The modern world offers endless illumination—but our bodies are designed for darkness, rhythm, and natural light.
Reclaiming control over your light—day, evening, and night—may be one of the most powerful biohacks for women’s health and hormonal balance.
Sources The Moon’s Phases, LED Light, and the Menstrual Cycle
Helfrich-Förster, C. et al. (2025). Synchronization of women’s menstruation with the Moon has decreased but remains detectable when gravitational pull is strong.
Science Advances. https://www.science.org/doi/10.1126/sciadv.adw4096Olcese, J. (2020). Melatonin and Female Reproduction: An Expanding Universe.
Frontiers in Endocrinology. https://www.frontiersin.org/articles/10.3389/fendo.2020.00085/full
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