Melatonin and Sleep

What does melatonin do?

We hear about internal body clocks and circadian rhythms, but what are they and how do they work?

Melatonin is a hormone, produced in the pineal gland in the brain from Seratonin. Amongst other functions, Melatonin regulates levels of sleepiness and our circadian rhythm.

woman asleep
Image: Danilo Rizzuti /

The pineal gland receives information about the light levels reaching the eyes. At night, when light levels are low (theoretically), Melatonin production increases and induces drowsiness. At dawn and throughout the day, when light levels are higher, melatonin levels are reduced.

Over time, your body gets used to this cycle and starts to get tired automatically at about the right time – this internal clock is your circadian rhythm. This is why you get jet-lag when you suddenly change time zones significantly – your built-in clock is initially still on the old time zone. Over a period of time your body adapts to the new cycles of light and dark and you gradually adopt the new time zone.

These systems evolved for thousands of years before the invention of electricity so it follows that if you artificially increase the levels of light at night, your melatonin levels will not be as high as they should be and sleep patterns may be compromised.

The amount of melatonin produced depends on:

  • the presence of Seratonin, and
  • signals regarding the levels of light sent to the pineal gland.


What does Serotonin do?

Serotonin is a neuro-transmitter – i.e. it passes signals between parts of the brain and is known to have a wide variety of functions, both physical and psychological, including influencing appetite and sexual desire.

Serotonin is also a hormone, found largely in the gut, but also in the bloodstream. Hormones are chemical substances which affect the function of organs but can also have a big effect on emotional and psychological things such as mood. Serotonin has been called the ’happy hormone’ (amongst other names along those lines) because its presence can lead to positive feelings, while an imbalance of Serotonin is thought to lead to anxiety and depression.

The chemical name for Serotonin in 5-hydroxytryptamine and, as we have seen, is used in the production of Melatonin. Serotonin itself is produced from another substance, 5 -hydroxytryptophan (5-HTP) which is converted from an amino acid, called Tryptophan.


What is Tryptophan?
Tryptophan (L-tryptophan, more accurately) is an essential amino acid. Amino acids are constituent elements of proteins, and ‘essential’ in this context means that the body doesn’t make its own so we rely on our diet to provide it.

Foods which contain Tryptophan include, most soy products, spinach, egg-white, black-eyed peas, walnuts, almonds, watercress, crustaceans such as crab and lobster, fish, such as halibut and cod and many more.

So the production line looks like this:

Tryptophan > 5-HTP > Serotonin > Melatonin


What is Adenosine?

Adenosine is another neuro-transmitter, like Serotonin, which seems to have a significant effect on our sleep. Adenosine is perhaps better known as part of the compound Adenosine Triphosphate, ATP, which is the energy source of the body’s cells.

Without the phosphate part, Adenosine is produced during the day and, at night, attaches to receptors in the brain which, in layman’s terms, switches off cells in ‘arousal centres’ and makes you feel drowsy. Overnight, the supply of Adenosine is used up, allowing you to wake up and feel more alert in the morning.

The fact that Adenosine has a link to the cellular energy source, ATP. may indicate that the need to sleep is connected to energy levels in the body.


How caffeine inhibits sleep?
Caffeine works by attaching to the same receptors as Adenosine, thereby preventing Adenosine from doing so but, because caffeine doesn’t do the ‘switching off’, it stimulates the brain and keeps you awake.


Tying it all together
So you need the proper levels of melatonin to be able to sleep: as it is produced when it is dark, that is why your bedroom should be dark for a good night’s sleep.

However, in order to keep your circadian rhythm working properly and to avoid feeling sleepy during the day, you also need to be exposed to good levels of light, preferably daylight, during the day (quite apart from the separate, but equally important, issue of getting sufficient Vitamin D).

Insufficient levels of Serotonin can have a double effect on preventing sleep by

  • not producing enough melatonin, and
  • causing emotional problems which can, in themselves, inhibit sleep.

As Tryptophan is required for the production of Serotonin and, because we get it through our food, a poor diet can also lead to a lack of Serotonin and Melatonin.

It is not only the levels of Tryptophan in the food we eat which matters, however. Insulin levels can have an effect as can Vitamin B6, which aids Serotonin production. As with most health issues, a good, balanced diet is therefore essential (which, in this context, means necessary!)

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