Melatonin & Your Cycle: The Sleep Hormone

You probably know melatonin as the supplement you reach for before a long flight or a rough night of sleep. But melatonin is so much more than a sleep aid. It is a hormone - one that your body produces every single night - and it has a surprisingly intimate relationship with your menstrual cycle, your reproductive hormones, and your overall hormonal health.

When melatonin is working well, you sleep deeply, your cycle runs smoothly, and your body has the antioxidant protection it needs. When melatonin is disrupted - by late-night screen time, shift work, or chronic stress - the ripple effects can show up as irregular periods, worsened PMS, poor egg quality, and even fertility challenges.

Here is what every cycling woman needs to know about the hormone that works while you sleep.

What Is Melatonin, and Where Does It Come From?

Melatonin is a hormone produced primarily by the pineal gland, a small structure deep in the brain. Its release is governed by light: when darkness falls, the pineal gland ramps up production, signalling to your body that it is time to wind down and sleep. When light returns in the morning, melatonin production drops, and you wake up.

This rhythm is called the circadian rhythm, and it is tightly woven into almost every biological process in your body - including the hormonal cascade that drives your menstrual cycle.

But the pineal gland is not the only source of melatonin. Your ovaries, uterus, and gut also produce it locally. This is a detail that changes everything when we talk about reproductive health, because it means melatonin is not just a sleep signal - it is an active participant in the ovarian cycle itself.

"Melatonin is found in high concentrations in follicular fluid surrounding developing eggs, suggesting it plays a direct protective role in ovarian function - far beyond its classic role as a sleep regulator."

- Dr. Russel Reiter, PhD, Professor of Cell Biology, University of Texas Health Science Center

How Melatonin Interacts With Your Reproductive Hormones

Your menstrual cycle is orchestrated by a precise hormonal conversation involving the hypothalamus, pituitary gland, and ovaries - what scientists call the HPG (hypothalamic-pituitary-gonadal) axis. Melatonin has receptors throughout this axis, which means it can influence hormonal signalling at multiple points.

Melatonin and LH

Luteinising hormone (LH) triggers ovulation. Research suggests that melatonin helps modulate the LH surge - the sharp rise in LH that causes the follicle to release an egg. Poor melatonin rhythms have been associated with blunted or mistimed LH surges, which can lead to delayed or absent ovulation.

Melatonin and Estrogen

Melatonin appears to have a moderating effect on estrogen. Some research indicates it can suppress excessive estrogen signalling, which may partly explain why women with disrupted melatonin rhythms - such as night-shift workers - have a higher incidence of estrogen-sensitive conditions like endometriosis and certain breast cancers. A review published via the National Institutes of Health highlighted melatonin's potential role as an anti-estrogenic agent in reproductive tissues.

Melatonin and Progesterone

The luteal phase - the second half of your cycle - is when progesterone takes centre stage, supporting the uterine lining and calming the nervous system. Melatonin appears to support progesterone secretion from the corpus luteum (the structure that forms after ovulation). Low melatonin has been linked to luteal phase defects, where progesterone production is insufficient and the luteal phase is too short.

Melatonin as an Antioxidant in the Ovaries

One of melatonin's lesser-known roles is as a potent antioxidant. Oxidative stress inside the ovarian follicle can damage developing eggs, impair fertilisation, and reduce egg quality. Melatonin, which concentrates in follicular fluid, helps neutralise these free radicals. This is why melatonin supplementation has become an area of active interest in reproductive medicine, particularly for women with poor ovarian reserve or those undergoing IVF.

What Disrupts Melatonin - and Why It Matters for Your Cycle

Modern life is essentially a melatonin-disruption machine. Here are the main culprits:

Artificial Light at Night

Blue light emitted by phones, tablets, and LED lighting suppresses melatonin production even at low intensities. Studies show that exposure to blue light in the two hours before bed can delay melatonin onset by up to 90 minutes, shrinking the window of peak melatonin production. For your cycle, this means a shorter, blunted melatonin peak - and less of its protective, hormone-balancing effects.

Shift Work and Irregular Sleep Schedules

Women who work night shifts or rotate shifts have significantly higher rates of menstrual irregularity, cycle length changes, and reduced fertility compared to women with regular sleep schedules. A large Harvard study found that rotating night-shift nurses had notably disrupted reproductive hormone profiles, consistent with melatonin suppression.

Stress and HPA Axis Activation

Chronic stress activates the HPA (hypothalamic-pituitary-adrenal) axis and elevates cortisol. Cortisol and melatonin have an inverse relationship: when cortisol is high at night (as it often is in chronically stressed individuals), melatonin production is blunted. This creates a vicious cycle where stress disrupts sleep, melatonin falls, and reproductive hormones become dysregulated.

Alcohol

Even moderate alcohol consumption in the evening has been shown to suppress melatonin levels by up to 19%, according to research published in the National Institute on Alcohol Abuse and Alcoholism's journal. For women already navigating PMS or cycle irregularity, this is worth considering.

Ageing

Melatonin production naturally declines with age, which is one reason sleep quality often worsens in the perimenopause years. This decline also coincides with dropping progesterone and estrogen levels, creating a compounding hormonal disruption that affects sleep, mood, and cycle regularity.

"We now understand that the decline in melatonin with age is not a passive side effect of ageing - it is an active contributor to the hormonal and reproductive changes women experience in their 40s and beyond. Supporting melatonin through lifestyle is a meaningful intervention."

- Dr. Sara Gottfried, MD, Integrative Gynaecologist and Author of "The Hormone Cure"

Melatonin Across Your Cycle Phases

Your sensitivity to melatonin and its effects may not be constant throughout your cycle. Here is how it maps onto each phase:

Menstrual Phase (Days 1-5)

Sleep is often disrupted in the days just before and during your period, partly due to falling progesterone and partly due to prostaglandins causing physical discomfort. Protecting melatonin during this phase - through earlier wind-down routines and dimmer light in the evening - can meaningfully improve sleep quality and reduce the intensity of period-related fatigue.

Follicular Phase (Days 6-13)

Rising estrogen in the follicular phase tends to improve sleep architecture and mood. Melatonin production is generally more stable during this phase. This is a good time to reinforce healthy sleep habits and circadian rhythm consistency.

Ovulatory Phase (Around Day 14)

The LH surge that triggers ovulation requires a well-functioning HPG axis - one that melatonin helps support. Some women notice a slight dip in sleep quality around ovulation, which may be related to the hormonal shift. Keeping evening light exposure low in the days around ovulation may help melatonin support a timely and robust ovulatory response.

Luteal Phase (Days 15-28)

This is where melatonin's role becomes most noticeable. As progesterone rises, it has a thermogenic effect (raising body temperature slightly), which can disrupt sleep architecture. Meanwhile, in women with PMS or PMDD, nighttime cortisol may spike, further blunting melatonin. Supporting melatonin through consistent sleep timing, darkness, and stress management is especially important in the late luteal phase when PMS symptoms peak.

How to Support Healthy Melatonin Naturally

Before reaching for a supplement, it is worth knowing that lifestyle factors can dramatically shift your melatonin rhythm. Here is where to start:

Get Morning Sunlight

Exposing your eyes to natural light within 30-60 minutes of waking anchors your circadian rhythm and sets up a stronger melatonin surge that evening. Even 10 minutes of outdoor light on a cloudy day is meaningful. This is one of the most evidence-backed interventions for circadian health.

Dim Lights After Sunset

Switch to warm, dim lighting in the evening. Use blue light filters on devices, or better yet, swap screens for books, gentle stretching, or conversation in the hour before bed. Your pineal gland begins releasing melatonin in response to darkness - so create the conditions for that to happen.

Keep Sleep Timing Consistent

Going to bed and waking at roughly the same time every day - yes, even weekends - is one of the most powerful ways to strengthen your circadian rhythm and melatonin output. Irregular sleep timing fragments melatonin pulses and reduces overall production.

Eat Melatonin-Supporting Foods

Certain foods are natural sources of melatonin or its precursor tryptophan. These include tart cherries (one of the richest dietary sources of melatonin), walnuts, eggs, dairy, turkey, oats, and bananas. A small tart cherry juice before bed has been shown in studies to raise melatonin levels and improve sleep quality.

Consider Supplementation Thoughtfully

Low-dose melatonin (0.5-1mg) taken 30-60 minutes before bed is generally considered effective and safe for short-term use. Higher doses (3-10mg, commonly sold in the US) are often unnecessary and may cause next-day grogginess or desensitise receptors over time. If you are using melatonin for cycle support or fertility, speak with a healthcare provider familiar with reproductive medicine before supplementing.

Melatonin, Fertility, and IVF

For women trying to conceive, melatonin has emerged as a promising area of research. Several small trials have found that melatonin supplementation (typically 3mg before bed) during IVF cycles improved egg quality and fertilisation rates, likely through its antioxidant protection of the follicular environment. While the evidence is not yet definitive enough for universal clinical recommendations, it is an area to discuss with a reproductive endocrinologist if egg quality is a concern.

Melatonin and PCOS

Women with PCOS often have disrupted circadian rhythms, poor sleep quality, and altered melatonin profiles. Research suggests that melatonin dysregulation may contribute to the insulin resistance and ovulatory dysfunction characteristic of PCOS. Prioritising circadian rhythm support - through consistent sleep timing and morning light exposure - may be a useful adjunct to other PCOS management strategies.