🔹 How sunset light cues your brain’s master clock and influences hormone timing 🔹 Why artificial light at night disrupts both sleep and reproductive signalling 🔹 The science of circadian rhythms in fertility: from ovulation and sperm quality to embryo development 🔹 Melatonin’s surprising role inside the ovaries and testes 🔹 What happens when the body loses track of time and what to do about it 🔹 A simple, daily ritual to bring your body and fertility into sync
The Alpaca and the Sunset
Years ago I was on a rural property with my then young daughters watching an alpaca give birth. Just one alpaca, in a clearing, mid-afternoon, new life unfolding.
What struck me as much as the miracle of birth was what mother alpaca and her fresh, spindly-legged baby did next. They simply sat there, side by side, watching the sunset.
The experience was awe inspiring. I remember thinking, even alpacas enjoy a beautiful sunset. What didn’t appreciate at the time was that they were also doing something else: they were tuning their biological clocks, syncing to time and winding themselves down.
The Biology of Sunset
Sunset is both scenic and a biochemical messenger.
The fading rays of dusk are dominated by longer wavelengths: reds, oranges and ambers. This warm spectrum, mesmerising to watch, also signals the master clock in your brain that night is coming.
When we work late at the office under fluorescent panels, and at home scroll & stream, we light up our evenings with flickering LEDs and blue-light backlit screens. The signal to stop has been drowned out by devices designed to keep us activated in the sympathetic state, producing cortisol and keeping melatonin under wraps.
Many of us already know this, but has it got to do with fertility?
How the Master Clock Sets the Stage for Conception
Yes, we have a menstrual cycle. But it doesn’t operate in isolation. Behind that monthly rhythm is a daily one: the circadian clock.
This clock is located in a part of the brain called the suprachiasmatic nucleus, or SCN. It responds to light, especially the contrast between morning and evening light, and sends timing signals to the rest of the body.
Why does this matter for fertility?
Hormone release isn’t random. It follows a rhythm. GnRH (Gonadotropin-releasing hormone), the hormone that kicks off the reproductive cascade, pulses in time with the circadian clock.
In women those pulses trigger LH (luteinising hormone) and FSH (follicle-stimulating hormone), which in turn drive egg maturation and ovulation. In fact, the mid-cycle LH surge, the signal that prompts ovulation, is precisely timed. It doesn’t just happen when estrogen is high. It happens when the hormonal environment and the circadian clock align.
As for sperm, testosterone secretion also follows a circadian rhythm, with levels peaking in the early morning and declining throughout the day.
This daily pattern is regulated by the SCN and can be flattened by circadian disruption. Sleep deprivation, late-night light exposure, shift work and chronic stress have all been shown to reduce testosterone levels and impair spermatogenesis, lowering both sperm count and quality.
Melatonin is more than a nocturnal, sleep-inducing hormone. It is a powerful antioxidant, synthesised not only in the brain but also within reproductive tissues, including the ovaries and testes.
In the ovary, melatonin protects developing follicles from oxidative stress and supports oocyte quality.
In the testes, it helps stabilise sperm DNA and supports normal testosterone production.
Melatonin’s synthesis is tightly linked to light exposure, particularly darkness. When that dark window is shortened by late-night screen use or artificial lighting, melatonin production drops, and the reproductive tissues lose one of their key protective signals during critical phases of maturation.
When You Fall Out of Sync
Disrupting the body’s internal clock can interfere with every stage of reproduction, from hormone regulation to embryo development.
In Females:
o Irregular menstrual cycles
o Anovulation (lack of ovulation)
o Longer time to conception
o Increased risk of miscarriage
o Possible links to endometriosis (via hormonal and inflammatory pathways)
In Males:
o Reduced testosterone (especially with late-night light exposure)
o Lower sperm concentration and motility
o Impaired spermatogenesis with chronic sleep disruption
In Early Pregnancy (animal models):
o Altered embryo development
o Disrupted placental function
Sunset as Medicine
A regular dose of sunset is your free, daily signal that helps bring your body back into rhythm.
You just need to step outside and look.
Let the sunset invite your hormones, nervous system, and reproductive clock to ease back into sync.
Tape This Onto Your Dimmer Dial
Step outside in the final 30–60 minutes before sunset
Leave your phone behind, or switch it to airplane mode
Watch the light change - no sunglasses
Stand or sit on natural ground if you can (grass, dirt, sand)
Let yourself do nothing for a few minutes
Use amber or red lighting indoors after dark, especially in the hour before bed
Keep lights low rather than overhead, like a true sunset
Dim your house as the sun dims. Let your home “set” too
Forget the downlights. We didn’t evolve with half a dozen suns overhead in the evening
Sleep in sync. Melatonin isn’t just for rest, it’s a fertility ally
Warmly, Sonja
If this sparked something for you, tap 🧡 and hit Restack to pass it on. Thanks for helping thoughtful fertility conversations travel further. 🤍
Curious to know more? Head to the About & Welcome pages for why I started Baby Ready Health and a bit about me.
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This post is for educational purposes only and is not medical advice. Always consult a qualified practitioner before making decisions about your health.
References:
Ono, M., Dai, Y., Fujiwara, T., Fujiwara, H., Daikoku, T., Ando, H., Kuji, N., & Nishi, H. (2025). Influence of lifestyle and the circadian clock on reproduction. Reproductive Medicine and Biology, 24. https://doi.org/10.1002/rmb2.12641
Sati, L. (2020). Chronodisruption: effects on reproduction, transgenerational health of offspring and epigenome. Reproduction, 160(5), R79–R94. https://doi.org/10.1530/rep-20-0298
Sciarra, F., Franceschini, E., Campolo, F., Gianfrilli, D., Pallotti, F., Paoli, D., Isidori, A., & Venneri, M. (2020). Disruption of Circadian Rhythms: A Crucial Factor in the Etiology of Infertility. International Journal of Molecular Sciences, 21. https://doi.org/10.3390/ijms21113943
Sen, A., & Sellix, M. (2016). The Circadian Timing System and Environmental Circadian Disruption: From Follicles to Fertility. Endocrinology, 157(9), 3366–3373. https://doi.org/10.1210/en.2016-1450
Thank you for the sunset solution 💛🧡❤️ and what a moment to witness animals so connected to the sun and natural rhythms