Twice a year, many of us adjust our clocks — an hour forward in spring, an hour back in autumn when clocks line up with the sun again — a practice that dates back to the early 20th century in the UK. The idea was simple: make better use of daylight, boost productivity, and align human activity with industrial needs. Adjusting our clocks might be a gesture toward efficiency — but not necessarily toward balance.
While our clocks may shift in an instant, our biology does not. Our bodies remain tuned to a rhythm far older than the mechanical clock — the rhythm of light and darkness, sunrise and sunset, rest and activity.
In Traditional Chinese Medicine (TCM), this principle is foundational. Health is understood as living in harmony with the Qi of nature — the vital energy that flows with the seasons, the elements, and the movement of the sun. The ancients taught that we should rise with the light, rest with the dark, eat and act in alignment with the natural cycles and seasons. To fight against nature’s timing was to invite imbalance.
Centuries later, modern science is rediscovering this truth. Through the lens of chronobiology or the study of biologic rhythms, we now understand that every cell in the human body operates according to an internal 24-hour rhythm known as the circadian rhythm. This rhythm regulates our hormones, metabolism, immune system — and yes, even our fertility.
And the key regulator of this rhythm is light.
Today, surrounded by artificial light and glowing screens, we’ve unintentionally dimmed the natural cues that keep our hormonal system in tune. Understanding how light interacts with our biology — and learning to live once again in rhythm with it — may be one of the simplest and most profound ways to support fertility and hormonal health.
The circadian rhythm: our body’s inner clock
Every cell in our body follows the same 24-hour pattern — a biological rhythm orchestrated by a small but powerful structure in the brain called the suprachiasmatic nucleus (SCN), located in the hypothalamus.
The SCN acts as the master clock, synchronising all other cellular clocks throughout the body. It receives signals directly from light-sensitive cells in the eyes that detect natural daylight. When sunlight enters the eyes in the morning, it tells the SCN that it’s time to wake, boosting alertness, regulating temperature, and initiating daytime hormone production.
As the sun sets and light fades, the pineal gland, a small, pea-sized endocrine structure located near the centre of the brain, releases melatonin, the “darkness hormone.” Melatonin not only prepares us for sleep but also plays a vital role in reproductive function — influencing ovulation, sperm quality, and the timing of hormonal release.
In short, light tells our body when to act; darkness tells it when to repair. The harmony between the two keeps every system, including fertility, in balance.
Light, hormones & energy: why timing matters
Light is one of the most powerful signals our body receives every day — and it affects much more than our mood or sleep. It regulates how our hormones, cells, and energy systems function. regulate the hypothalamic–pituitary–gonadal (HPG) axis, the network that controls reproduction.
Cortisol rhythm: During the day, natural light entering the eyes tells the brain that it’s time to wake up. Morning light triggers cortisol release, our natural “wake-up” hormone, which supports energy, focus, thyroid function, and reproductive hormone production. When cortisol peaks in the morning, it sets the rhythm for the entire day. When cortisol rises at the right time and declines gently in the evening, the body maintains hormonal harmony. Disrupted light exposure, however, can flatten this rhythm, leading to fatigue, mood changes, and disturbed menstrual cycles.
· Melatonin and fertility: As light fades in the evening, the body should naturally increase melatonin, the hormone of darkness. Melatonin helps us fall asleep, but it’s also a powerful antioxidant that protects eggs and sperm, supports immune balance, and helps the mitochondria, the “energy factories” of our cells, produce energy efficiently. These mitochondria are where many sex hormones begin their synthesis.
Oestrogen and progesterone: Melatonin helps regulate GnRH (gonadotropin-releasing hormone), which controls ovulation in women and testosterone production in men. Irregular light patterns and late-night exposure to artificial light have been linked to menstrual irregularities and polycystic ovary syndrome (PCOS).
Our reproductive hormones are rhythmic by design — and light is like the metronome that keeps them in time.
The modern problem: artificial light and screen exposure
For most of human history, our lives were guided by the natural cycle of day and night. We rose with the sunrise, worked in daylight, and rested when the world grew dark.
Today, artificial light keeps us in a perpetual state of “twilight.” We spend up to 90% of our time indoors, under fluorescent bulbs and LED screens that mimic daylight at the wrong time of day. This modern light exposure confuses our internal clock:
· In the evening, blue light, the dominant wavelength emitted by screens, is especially disruptive. It tricks the brain into thinking it’s still daytime, suppressing melatonin and delaying the onset of sleep and repair. Even brief exposure can reduce melatonin production by up to 50%. Over time, this misalignment leads to chronic sleep deprivation, hormonal imbalance, and potential reduced fertility
In the morning, not getting enough natural light prevents a healthy cortisol rise, leaving us tired and hormonally out of sync.
For women, disturbed melatonin and cortisol rhythms can interfere with ovulation timing and cycle regularity. For men, studies show that evening screen use correlates with lower sperm concentration and motility.
It’s not technology itself that harms us — it’s the timing. Our biology still expects bright natural light in the morning, and deep darkness at night.
Over time, this mismatch can affect ovulation, sperm quality, stress resilience, and energy levels. Chronic stress or “burnout” further depletes cortisol production and disrupts the hormonal cascade that also governs fertility.
The solution is simple but powerful: reconnect with natural light.This simple habit helps your hormones, mitochondria, and stress systems stay aligned — supporting not only better sleep and energy but also long-term fertility and vitality.
Reconnecting with natural light: simple, powerful steps
The beauty of this knowledge is that we can act on it immediately. By adjusting how and when we expose ourselves to light, we can profoundly influence our hormones, energy, and fertility.
Seek morning sunlight.
Step outside within an hour of waking for 10–15 minutes. Morning light resets your circadian rhythm, boosts serotonin (the precursor to melatonin), and supports healthy cortisol levels.Dim the lights in the evening.
Reduce bright, artificial lighting and screen use 1–2 hours before bed. Opt for warm-toned bulbs (yellow, orange, red) or use blue-light filters.Sleep in darkness.
Even small light sources — streetlamps, device LEDs — can suppress melatonin. Use blackout curtains or a sleep mask for deeper rest.Keep a regular schedule.
Go to bed and wake up at consistent times, even on weekends. Hormones thrive on rhythm and predictability.Nourish your light metabolism.
Light doesn’t work in isolation — it partners with nutrition. Morning sunlight activates mitochondria, your cells’ energy centres. Food full of nutrients like magnesium, vitamin D, and antioxidants help these cells use light more efficiently.
The deeper message: harmony between light and life
Relearning how to live in tune with light isn’t about nostalgia or restriction. It’s about about returning to a natural intelligence that modern science is finally beginning to measure — one that ancient traditions have honoured for millennia.
Our clocks may support productivity, but our biology follows the sun. If we want to nurture hormonal balance and fertility, we must once again learn to live in rhythm with light.
If you’re curious about how acupuncture and Chinese Medicine principles could support you, your hormonal balance, menstrual cycles, fertility, or your health in perimenopause and menopause, email me at Sophie@silverwoodacupuncture.co.uk. We can book a FREE call and I will answer any of your questions.
My Clinics:
• Clapham (South London) – makemefeelparapharmacie •
• Chancery Lane (Central London) - 2MeClinic • an incredible hub dedicated to female heath, founded by Dr Anne & Dr Uchenna, with an amazing team: GPs, nutritionists , psychotherapists, and… me, your acupuncturist
To book an appointment click here
Sources
Khalsa SB, Jewett ME, Cajochen C, Czeisler CA. Immediate effect of blue-enhanced light on reproductive hormones in women. PLoS One. 2015.
Touitou Y, Bogdan A, Lévi F. Sleep and Reproductive Health. J Circadian Rhythms. 2020;18:1.
Gamble KL, Motsinger-Reif AA, Hida A, et al. Integration of Circadian and Metabolic Control of Reproductive Function. Endocrinology. 2018;159(11):3661-74.
Choi B-I, Bertram J, Gong H-Y, et al. Effects of Blue Light on Puberty and Ovary in Female Rats. J Clin Res Pediatr Endocrinol. 2023;15(1):28-37.
Mauvoisin D, Jörg-Appelgren M, Claustrat B, et al. Melatonin and stable circadian rhythms optimize maternal, placental and fetal physiology. Hum Reprod Update. 2013;20(2):293-307.
Wang F, Zhang L, Shimoda M, et al. The Circadian Timing System and Environmental Circadian Disruption: From Follicles to Fertility. Hum Reprod. 2016;31(12):2881-2895.
Light Exposure, Melatonin Secretion, and Menstrual Cycle Parameters: An Integrative Review https://www.researchgate.net/publicat...