The Serotonin and Melatonin Link for Sleep Disorders, Brain Health & More

Serotonin and Melatonin are both neurotransmitters derived from the essential amino acid L-Tryptophan, found in protein. These brain messengers are important for regulating our sleep cycles and our moods.

If we become deficient in either, it can lead to disruptions in sleep patterns and lessen the time spent in restorative deep sleep stages.

By increasing levels of Serotonin and Melatonin precursors in the diet or with supplements, it may be possible to improve sleep habits as well as enhance the mood.

Since Tryptophan cannot be made in the body, we must get it from foods we eat or through supplementation to make these neurotransmitters. Tryptophan is a precursor for 5-HTP, which is subsequently a precursor to Serotonin and Melatonin. Therefore, Tryptophan or 5-HTP may increase levels of both Serotonin and Melatonin in the body.

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What are Serotonin and Melatonin?

Tryptophan is an amino acid that is found in all complete proteins such as red meat, poultry, eggs, and dairy products, as well as some incomplete proteins such as some vegetables, fruits, and nuts.

Tryptophan from the diet or supplements is broken down in the liver into 5-HTP and other metabolites including niacin (Vitamin B3). The 5-HTP travels through the bloodstream to the brain, crosses over the blood-brain barrier, and enters the brain tissue. Once in the brain, the 5-HTP is converted into Serotonin.

Serotonin is a monoamine neurotransmitter that increases feelings of happiness and contentment. Serotonin is also responsible for efficiency of food digestion and mood regulation. Serotonin can be found in cells in the brain and digestive system and transported in the bloodstream.

Since Serotonin cannot cross the blood-brain barrier, any Serotonin needed in the brain must be produced there. Serotonin is also produced in the digestive system in specialized cells and taken up by platelets via special protein transporters. Serotonin in the gut causes peristalsis (rhythmic contractions) to occur, aiding in digestion.

Some physiological and behavioral functions are primarily related to the metabolism of Tryptophan and 5-HTP into Serotonin and Melatonin including sleep, wakefulness and mood, cravings and control of senses. Effects of low Serotonin on the central nervous system has been linked to some behavior and cognitive disorders such as depression, anxiety and even insomnia.

Melatonin is a neurotransmitter also derived from the amino acid Tryptophan through the conversion of Serotonin. During the daytime, production of Serotonin is high and production of Melatonin is low. The pineal gland in the brain switches to converting higher levels of Serotonin into Melatonin when there are lower levels of light in the ambient environment. This forms the basis for our natural circadian rhythms, or 24-hour day cycle.

The effects of Melatonin have been studied in detail and correlated to processes such as the regulation of sleep. Low levels of Melatonin in the brain have been linked to restless sleep and in some cases insomnia. Low levels of Melatonin may also be linked to other brain conditions such as Alzheimer’s disease.

The Relationship Between Serotonin and Melatonin for Sleep

Sleep disturbances may be due to low levels of Serotonin available for conversion into Melatonin.

During the day, hormones like Serotonin are high in the body to carry out daily tasks. During the evening, Serotonin levels drop and Melatonin levels rise, preparing the body for sleep.

A normal drop in Serotonin, along with other inhibitory hormones, causes an increase in Melatonin production. In contrast, a normal drop of Melatonin in the morning leads to Serotonin rising again.

Since Serotonin is a precursor for Melatonin, Serotonin deficiencies can lead to sleep disorders and insomnia. Insomnia is a condition where sleep is disturbed through trouble getting to sleep, trouble staying sleep and waking up too early in the morning.

Symptoms of insomnia may also include feeling sleepy during the day, lack of focus, feelings of irritability, tension headaches, and ongoing worries about sleep. The long-term effects of this disorder can be damaging, as our bodies require periods of deep sleep to perform maintenance and replenish levels of necessary neurotransmitters and hormones.

When areas in the brain that control sleep are altered, sleep patterns may be severely disrupted or abolished. In studies where Serotonin was artificially embedded in those same areas, levels of Melatonin were increased and sleep was induced.

It has been noted that the effects of Serotonin on inducing sleep occurs through the direct transmission of the neurotransmitter Melatonin. Melatonin is the direct result of the biosynthesis of Serotonin from Tryptophan and 5-HTP.

Serotonin levels peak in the daytime and are subsequently converted into Melatonin in the evening by the pineal gland. Therefore, supplementation of 5-HTP in the evening or before bed may increase levels of Melatonin needed for a restful sleep.

Melatonin and Brain Health

Low Melatonin levels in the brain may be linked to the onset of Alzheimer’s. Levels found in the brain and spinal fluid seem to decrease in the body with age. As this decrease of Melatonin is observed, instances of Alzheimer’s seem to increase.

In one study done on patients of all ages with Alzheimer’s, low levels of this hormone were observed. Some of these patients were young adults that had both low levels of Melatonin and symptoms of Alzheimer’s.

This finding increased interest in the correlation between this condition and this well-known sleep hormone. There are on-going studies also looking into the effect of Melatonin and early onset of Alzheimer’s.

The brain receives the precursors Tryptophan and 5-HTP in order to make Serotonin and Melatonin. Many mood and sleep disorders are related to low levels of one or both of these neurotransmitters. In these cases, increasing Tryptophan in the diet and/or supplementing with 5-HTP may increase production of Serotonin and Melatonin.

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