Why 2010 Changed Women’s Hormones, and No One Noticed
How Modern Light Broke an Ancient Hormonal CodeFor most of human history, women’s cycles moved with the Moon.Until about 2010, when that connection faded without anyone really noticing (until now)... A new study published in Science Advances (Helfrich-Förster et al., 2025) found something extraordinary: for thousands of years, women’s reproductive rhythms were synchronized with lunar light and gravity. Then, suddenly - within just over a decade - that synchrony faded from view. When I first read the paper, I felt what I imagine you will - a mix of awe and heartbreak......because once again - it’s not that our biology changed, it's that our environment did. Keep reading for the full article! ⏰ Want to stay in sync this fall & Winter? Check out Quantum Winter Blueprint (now with the brand new Fall Time Change Ebook): seasonal food lists - recipes - cold therapy & red light therapy strategies for fall/winter & more - click here to get the details 🧼 My favorite low tox laundry deal is ending soon! $39 Bundle Deal *comes with free washing machine cleaner* (when was the last time you cleaned your machine ? 😅 click here to get the deal New here? Get my $5 Seasonal Food Guide or my $7 Cortisol Course - or Download MyCircadianApp for free All my favorite things - Free Product Guide What the 2025 Study Found:Researchers analyzed 3,000+ menstrual cycles collected over multiple decades. They found that:
This doesn’t mean every woman was in the same phase at once. It means our population pattern, and the collective timing of ovulation and menstruation was once tuned to the same lunar rhythm. How all of this ties into Circadian Biology (why this isn't woo-woo):The average menstrual cycle lasts about 29.5 days, nearly identical to the lunar cycle’s 29.53 days (Cutler et al., Psychoneuroendocrinology, 1986). The very word “menstruation” comes from mene - Greek for moon. Light and darkness are not just visual experiences; they’re biological instructions.
This is why I always call melatonin a powerful reproductive hormone, and we also used to see more babies born at night under a full moon & during the day under new moons (Novel perspectives on the influence of the lunar cycle on the timing of full-term human births: https://doi.org/10.1080/07420528.2020.1785485). What about 28 day Cycles? The idea that a “normal” menstrual cycle is 28 days long comes from medical standardization. Early 20th-century research and later birth control pill design adopted a 28-day framework simply because it fit the Gregorian calendar and made prescribing predictable. In reality, healthy cycles range from about 26–32 days, and the true biological average is closer to 29.5 days - the length of a lunar month. Historically, many women’s cycles aligned with the Moon’s phases, which is why words like “month” and “menstruation” share the same root (mene, meaning “moon”). So while 28 days became a convenient cultural norm, it’s not what nature designed! What Changed Around 2010: Artificial light isn’t new...However - spectral quality and timing of our light exposure changed dramatically around 2010 - when LED bulbs replaced incandescents and smartphones became universal - affordable & accessible to all. LEDs emit intense blue light peaks that suppress melatonin 3- 5 times more strongly than older bulbs (West et al., Lighting Research & Technology, 2011; Gooley et al., J Clin Endocrinol Metab*, 2011), and because of this - for the first time in human history, we began exposing our retinas to high-intensity, short-wavelength light long after sunset. Moonlight averages under 0.1 lux, while a smartphone at arm’s length can exceed 30–50 lux: hundreds of times brighter than anything our biology evolved to experience at night. Beyond brightness, our phones emit mostly blue and green wavelengths - the exact signals your brain uses to tell time. hese wavelengths trick your circadian system into thinking it’s still daytime, even hours after sunset. So it's important to understand that this shift in the way we used light at night didn’t just change our sleep- It rewired hormonal timing itself. (Timeline: Candlelight → Incandescent → LED → Smartphone glow) Melatonin isn’t merely a “sleep hormone" - it's a reproductive synchronizer and a mitochondrial protector:
Suppressing melatonin through artificial light, shift work, or late-night screen use, not only destroys your sleep signal, but your hormones! When melatonin falls out of rhythm, every downstream hormone - from estrogen to thyroid to cortisol - loses its place in the hormonal symphony. This is why restoring melatonin rhythm isn’t optional for women’s health - it’s foundational. The Bigger Picture: Leptin, Melatonin, and the Master HormonesThis study is a reminder that true hormonal balance starts with timing, not with chasing individual hormones. Melatonin, leptin, and cortisol are the master timekeepers of your endocrine system.
The good news - it's not complicated: When you realign light exposure, mealtimes, and circadian rhythm, your hormones have a much easier time remembering the code. I've seen it (and experienced it) firsthand - hundreds of women reporting: ✨ restored cycles ✨ effortless weight loss ✨ fertility after years of “unexplained” infertility ✨ balanced perimenopause and menopause ✨ deeper sleep and steady energy Here are two testimonials that just came in this week ⬇️⬇️ If this resonates, I teach this entire process inside my Leptin Reset and Leptin Master Plan (advanced level).Y ou’ll learn how to use light, food timing, and circadian signals to reset the hormones that control every other hormone -melatonin, leptin, and cortisol. Join the thousands of women (and men!) who’ve reclaimed their cycles, restored their sleep, and even conceived naturally - just by restoring the timing nature designed. Click here for 15% off the Leptin Reset Click here for the Leptin Master Plan (advanced learners & practitioners) Please feel free to forward this article to a friend or family member who might find this interesting. Reading this on the web or forwarded from a a friend? Click here to subscribe so you don't miss free informative content in the future.Enjoy my work & want to support me? (No pressure as this newsletter will remain free) Leave me a tip!
In Health🌞, Sarah PS - This newsletter is not medical advice nor a substitute for 1:1 care with a trusted practitioner! |
