Melatonin is a hormone released by the pineal gland, a pea-sized gland located in the centre of the brain.
Melatonin plays an important role in controlling circadian rhythm and the sleep-wake cycle.
There is a relationship between light exposure and melatonin. Exposure to bright light (e.g., in the morning) reduces melatonin, and levels rise in dark environments (e.g., at night).
CLINICAL RELEVANCE
Exposure to light in the evening strongly suppresses melatonin, resulting in difficulty falling asleep and a phase shift in the sleep pattern, with later sleep onset and difficulty waking early in the morning. Delayed sleep phase syndrome (DSPS) involves an onset of sleep and waking more than two hours later than desired.
Function
Melatonin promotes the onset of sleep. The levels rise in the evening, peak in the middle of the night, fall in the morning and remain low during the day.
Melatonin receptors (MT1 and MT2) are found throughout the body. Notably, they are found in the suprachiasmatic nucleus, a structure in the anterior hypothalamus responsible for circadian rhythm.
In addition to promoting sleep and contributing to circadian rhythm, it also helps:
- Lower the body temperature
- Lower the blood pressure
Disruption
Disruption to melatonin and the circadian rhythm may occur with:
- Delayed sleep phase syndrome (DSPS)
- Shift work (e.g., variable working between night and day shifts)
- Jet lag
- Seasonal affective disorder (potentially involving increased melatonin during dark winter months)
- Autistic spectrum disorder (which may be associated with low melatonin levels)
Melatonin levels decline with increasing age.
Medications
Melatonin is used to treat sleep disorders. It may be short-term when treating insomnia and jet lag or longer-term when treating sleep disorders associated with chronic conditions (e.g., learning disability).
Last updated September 2024
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