What's the Deal With Melatonin?

What’s the Deal With Melatonin?

As a sleep doctor I am often asked to talk at medical conferences, teach on courses and give talks to medical trainees and consultants. At almost all of these events I probably get asked more questions about melatonin than any other medication. In this blog I will tell you a little bit about this really interesting medication.

 

What is melatonin and how is it controlled?

Melatonin is a hormone produced in a small gland in your brain called the pineal gland. The French scientist and philosopher, René Descartes, thought this gland was the seat of the soul as it seemed to be the only part of the brain where there was only one version rather than there being one in the left brain and one in the right. Melatonin is found throughout the animal kingdom and in many plants as well so it is probably a very old hormone. In animals, including humans, melatonin is secreted at night and acts as a signal to the rest of the brain and the body that it’s nighttime. There are receptors for melatonin all over your body and the time signal from melatonin helps to keep all the different parts of your body working in concert with each other. Things would go haywire if one part of your body thought it was day and another part was behaving as if it was night!

 

The release of melatonin is controlled by the master clock which is found in a part of the brain called the suprachiasmatic nuclei or SCN. The SCN has its own innate rhythm which is usually slightly longer than 24 hours. So, if it were left it its own devices the release of melatonin would gradually drift out of sync with the outside world. Fortunately, the SCN, and therefore the melatonin rhythm, is continuously being recalibrated by external cues, especially by light. During the day light stimulates the SCN which inhibits melatonin secretion. At night, when the light levels drop the SCN becomes less active and melatonin is released. Melatonin also feeds back to the SCN and inhibits its activity, thus promoting further melatonin secretion.

 

Melatonin can be used to correct a body clock that’s out of sync.

If melatonin acts as a time signal to the body it means we can use it to adjust the body clock when it gets out of sync with the outside world. So we use melatonin tablets or liquids for treating body clock disorders like delayed sleep wake phase disorder when the body clock is running behind the external time. People with this condition feel like their body is in the UK but their body clock is in New York and they struggle to fall asleep until very late. If left to their own devices they would wake up late as well but often they aren’t able to do that and so their sleep opportunity is restricted and they become very sleep deprived. By giving carefully timed melatonin we can pull their body clock forward so they can fall asleep and wake up at a normal time.

 

Another common body clock disorder is jet lag. Here you are taking a perfectly normal body clock and moving it to a different time zone so the internal and external clocks are no longer in sync. Eventually the internal clock will adjust to the new time zone, but melatonin can accelerate this process.

Melatonin can be used as a sleeping pill.

 

Another thing that melatonin does to humans is that it makes us feel a bit sleepy. This is partly due to the time signal effect of the hormone telling our brain it is night time but it also has a direct soporific effect entirely aside from the time signal. This effect is not found in all animals though. Nocturnal animals like rats still secrete melatonin at night yet they are awake at night and sleep in the day when melatonin levels are low. But in humans we can use the sedating effects of melatonin to enhance sleep and it is used as a sleeping pill to treat insomnia.

 

Melatonin can stop people from acting out their dreams.

So melatonin is useful for helping to people to sleep better and at the right time. But in the sleep world we also have another, unexpected use for melatonin and that is to treat a condition called REM sleep behaviour disorder (RBD). When we go into REM sleep, which is where we do most of our dreaming, we should be completely paralysed. The reason for this is that, if you dream you’re kicking a football, the part of your brain that controls your muscles is firing, trying to a get your leg to kick that ball. Clearly, playing football in the bed when you’re asleep is not a good thing. So when you go into REM sleep your brain sets up a roadblock to stop the signals getting from your brain to your muscles. But in RBD that roadblock is not set up and so people act out their dreams in the bed. People with RBD will punch, kick and shout out in their sleep and this can lead to them injuring themselves or their bed partners. For reasons we really don’t understand taking melatonin re-establishes the roadblock and stops the dream enactment.

 

Final thoughts:

It's important to say that for each of these three uses we may need to use very different doses of melatonin and the timing of the medication can be crucial. So, although one can buy melatonin off the shelf in many countries, if one needs melatonin it is best to get it prescribed by a knowledgeable clinician who can determine if it is the right medication, and can prescribe the right dose at the right time. Another reason to avoid buying melatonin on the internet or whilst on holiday is that in many countries it is classed as dietary supplement rather than a medication. That means it is easier to get but the quality control of dietary supplements is rarely as good as the quality control of medications.