When are serotonin levels highest or lowest?

As one of the most important neurotransmitters, serotonin fulfills many different tasks in the central and peripheral nervous system. The concentration of serotonin in the body can fluctuate depending on the time of day as well as on various external factors.

When is the serotonin level at its highest?

Research suggests that serotonin production in the body fluctuates throughout the day and is highest during the day. Studies with animals have shown that serotonin levels are highest in the evening with the onset of darkness [1], but beyond that, it also depends on the availability of tryptophan.

Tryptophan is an amino acid from which serotonin is formed. The conversion to serotonin occurs in two steps: First, tryptophan is converted to 5-HTP, which is then converted to serotonin. The more tryptophan or 5-HTP is available, the more serotonin the body can produce. This is helped by various external influencing factors such as sport or regular exercise, a balanced diet, little stress and good mood [2].

However, probably one of the strongest influencing factors on serotonin formation is daylight, which has been shown to stimulate serotonin production. This is the reason why serotonin levels are higher during the day than at night and higher in summer than in winter. The "winter blues" often seen in the dark season are probably due to a serotonin deficiency.

When is the serotonin level at its lowest?

At night, the body begins to break down serotonin and convert it into the sleep hormone melatonin. This is done by enzymes that only become active when darkness sets in. Thanks to them, the body produces about ten times as much melatonin at night as during the day. As a result, serotonin levels drop and are lowest in the morning.

What are the serotonin normal levels?

Regardless of diurnal and seasonal variations, there are serotonin normal levels. This is the range in which serotonin levels usually lie in healthy individuals. Serotonin normal values can refer either to the amount of serotonin in blood serum [3] or to the serotonin breakdown product HIES [4], which is excreted in urine:

• Serotonin normal values from blood serum: 50 - 200 µg/ l.
• HIES normal values from urine: xtagstartz 9 mg/24-hour collection urine.