How Does Melatonin Affect Sleep?

8 Min Read | By Nat Took

Last Modified 13 March 2024   First Added 21 July 2020

This article was written and reviewed in line with our editorial policy.

Melatonin definition:

n. an amine hormone, produced mainly by the pineal gland as a metabolic product of the neurotransmitter serotonin, that helps to regulate seasonal changes in physiology and may also influence puberty. It is implicated in the initiation of sleep and in the regulation of the sleep–wake cycle. Melatonin has been investigated in clinical studies as a hypnotic and for the management of circadian rhythm sleep disorders. Although these studies are as yet inconclusive, melatonin is widely available as an over-the-counter medication.

What is melatonin?

Melatonin is a hormone that is naturally produced by the body. The hormone signals to the body that it is time to sleep. That’s why it’s often called the “sleep hormone”.

Discovered in 1958 by American physician Aaron B. Lerner and his colleagues at Yale University School of Medicine, melatonin was named for its ability to reverse the skin darkening effects of melanocyte-stimulating hormone. The chemical formula for melatonin is C13H16N2O2 meaning it contains thirteen atoms of carbon, sixteen of hydrogen, two of nitrogen and two of oxygen which are synthesised by the body through a variety of chemical processes from another hormone called L-tryptophan.

Released in humans by a small, pea-shaped endocrine gland in the brain called the pineal gland, melatonin is a hormone commonly associated with sleep. It’s released as it gets dark around you, making you feel ready to sleep at night, though is more accurately a regulating hormone that plays a part in many animal and botanical functions. This ranges from helping to synchronise circadian rhythms to triggering seasonal fattening, moulting and hibernation of animals. Melatonin is even responsible for defending against oxidative stress in plants.

Commonly used in the treatments of sleep disorders, though with mixed evidence of efficacy, it is a prescription-only medication in the UK. It is approved for medical use in the European Union, but has not received approval for medical use by the Food and Drug Administration (FDA) in the US.

Despite its uncertain effects as a medication, however, its role in the human body is not disputed – it plays an important part in the regulation of sleep cycles. The production of melatonin is directly influenced by the detection of darkness by the retina. In short, our bodies inhibit production of this sleep hormone when our environments are bright. On the flip side, dark bedrooms and a lack of light encourage it to be released.

A second and interesting role of melatonin in the body is its connection to ageing. Melatonin is both an antioxidant and connected to the modulation of certain functions of the immune system. Its production declines with age, leading to scientific associations between melatonin and a number of age-related diseases.

So, what exactly are hormones?

Hormones are the body’s chemical messengers. They are released by endocrine glands and travel through your bloodstream to different parts of the body. They tell different tissues and muscles what to do.

There are three classes of hormones:

  • Eicosanoids;
  • Steroids;
  • Amino Acids.

Within these classes, hormones have a wide variety of chemical structures. The hormone binds to specific receptor proteins in cells which lead to the cell changing its function.

Hormones affect many processes in the body, such as mood, growth and metabolism. Generally, they regulate physiology and behaviour.

How melatonin regulates sleep

When you’re exposed to light, the light travels down the optic nerve of the eye until it reaches the SCN. The SCN then signals the pineal gland to produce hormones such as cortisol and to raise your body temperature, which causes you to start waking up. The SCN also inhibits the release of melatonin at this time. In the evening, when not as much light enters the optic nerve, the SCN stops inhibiting melatonin, which then signals the sleep process.

How can understanding melatonin help you sleep better?

If you’re having difficulty sleeping, it could be due to your exposure to light, which confuses your signalling system. Jason Piper, a certified sleep coach and founder of Build Better Sleep told us:

Melatonin is also known as the Dracula hormone because it only comes out at night. It is produced in the pineal gland and released when it is dark out. It helps us to feel sleepy, entrain our circadian rhythm, and is the body’s strongest antioxidant.

The body has natural rhythms that wake us up and put us to sleep. This is very useful. In the morning our cortisol levels naturally rise to wake us up and prime us for the day. Cortisol is useful in the morning as it makes us alert, clear thinking, and gives us energy. At night as the sun sets, our eyes register the changing light and melatonin is released so that we feel sleepy, so we can rest and repair the body overnight.

If you think back to a time before electricity, this worked perfectly. We were up at daylight to hunt,  farm, and gather. All of the days’ activities were done during daylight hours and then night time was dedicated to sleeping.

Fast forward to today, and most of us are living disconnected from our biological clocks and this is wreaking havoc on our bodies. We wake up and head off to spend most of the day inside a building under dim lighting, compared to the sun. We then come home and turn on bright lights, compared to what’s outside when it’s dark. This action tells the body it’s still daytime. This is why a number of people are having a hard time falling asleep. They are sending mixed signals to their brain.

Tips for better sleep naturally

As sleep is naturally regulated by day and night, it stands to reason that artificial light causes some of us to find it difficult to sleep. Blue light found in energy-efficient lighting and screens seems, in particular, to be disruptive. But it’s not all about light; there are other areas that can also affect how well you sleep. If you want to sleep better naturally, try the following:

1. Reduce blue light exposure in the evening
2. Increase your exposure to natural daylight
3. Reduce your caffeine intake later in the day
4. Have consistent bed and waking times
5. Minimise noise and light in the bedroom

Using melatonin supplements

If you are finding it harder to sleep, you could try a melatonin supplement to help you to sleep. In the UK, melatonin is available as a prescription-only medicine and so needs to be prescribed by your GP. By taking melatonin, you may help to regulate your body’s sleep cycle.

However, it is important to remember that melatonin is only licensed in the UK for short-term use for sleep issues such as jetlag. If you are suffering from long-term sleep problems or a sleep disorder, there will be other pathways through your doctor.

Do melatonin supplements work?

There’s not enough evidence to clearly say whether or not taking melatonin for sleep works. Some studies show that they do, whereas others indicate the opposite. Every person also reacts differently to supplements.

There is evidence that melatonin can reset the body clock. However, it’s not clear if exposure to light is more effective. The research does suggest that if melatonin is taken at an appropriate time it can improve sleep when used for shift work and jet lag.

Dr Bay Kelly comments on melatonin supplements:

Melatonin supplementation in doses ranging from 1-5 mg have been shown to be effective in those with trouble sleeping due to jet lag or shift work.

However, she adds advice on how to naturally support melatonin production:

Melatonin is produced by transforming an amino acid called tryptophan, meaning that dietary factors can affect melatonin production. Tryptophan can be found in foods such as chicken, dairy products, eggs, spinach, nuts, seeds and salmon. It’s also important to know that in order for your body to produce sufficient amounts of melatonin from tryptophan, sufficient amounts of zinc, B6 and magnesium are needed.

Side effects:

Melatonin is generally considered safe, with fewer side effects than other sleeping medicines. If you experience any adverse reactions or changes to how you normally feel, contact your doctor as soon as possible.

It’s also important to note that melatonin can cause issues if you’re taking other medicines, such as birth control and diabetes drugs.

What effect does synthetic melatonin have on the body?

While we know the importance of biosynthesised melatonin to the body and various bodily functions, the impact of synthetic melatonin is less well understood. However, melatonin has shown greater than placebo effects for a variety of sleep related issues including the onset of sleep, total sleep duration and sleep efficiency.

Evidence of efficacy has led to the use of melatonin for the following conditions:

  • Jet lag: While evidence is more comprehensive for the efficacy of melatonin for eastward flights, reviews in 2010 and 2014 found better than placebo improvements in sleep for jet lag.
  • Delayed sleep-wake phase disorder: Melatonin was found in a randomised trial to improve the quality of sleep and sleep onset.
  • Anxiety prior to surgery: A 2015 review found strong evidence that melatonin reduced anxiety prior to surgery.
Overall, it is best to try and improve your sleep naturally instead of using supplements, as there can be a lot of underlying causes or behaviours that are disrupting your sleep pattern.

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