Serotonin is a much-studied neurotransmitter --- a chemical that transmits signals from one nerve cell to another --- because of its contribution to mental well-being and mood. Once formed in the brain, serotonin plays a role in blood cells, the lining of the digestive tract and the central nervous system. It's best known for creating a sense of "satisfaction" after the consumption of food and promoting sleep and relaxation. There is only one method by which serotonin is derived, and that's through the amino acid known as tryptophan.
Tryptophan
Amino acids play a critical role as the building blocks of proteins, a group of nutrients upon which every cellular process in your body depends. There are two main types of amino acids: essential amino acids such as tryptophan that you obtain exclusively from your diet and nonessential amino acids produced by the cells independent of their consumption. Tryptophan is an important and ubiquitous nutrient found in eggs, fish, poultry, red meat, dairy, oats, peanuts, seeds and soy.
Correlation
The rate at which nerve cells produce neurotransmitters is dependent upon the availability of "precursor" molecules; in other words, the molecules that must be present to create the end product. Tryptophan is a precursor of serotonin; nothing else but tryptophan can create it. The transformation of a molecule such as tryptophan into another is facilitated by what is known as a "metabolic pathway." The serotonin pathway involves two different "intermediate molecules" that bridge the gap. Through this relatively simple pathway the correlation between tryptophan and serotonin is quite strong. A 1980 study published in "Pharmacological Reviews" found that the ingestion of tryptophan raises brain tryptophan levels, which in turn accelerates the synthesis and release of serotonin. Conversely, a paucity of tryptophan within the body lowers serotonin levels between 30 minutes to 2 hours after the amino acid's depletion.
Factors Influencing Production
The conversion rate of tryptophan into serotonin is actually affected by several different factors. Consuming protein-rich foods, for example, may slow down serotonin production, because other amino acids compete with tryptophan for transportation across the blood-brain barrier. Conversely, a larger proportion of tryptophan in the blood will cross the barrier and increase the rate of serotonin production. This process is aided by the consumption of carbohydrates, which trigger the release of a hormone known as insulin. Insulin lowers the blood levels of most amino acids except for tryptophan. Vitamin B-6 is also necessary for the conversion of tryptophan into serotonin. Any of these factors may ultimately influence the amount of serotonin available to the brain.
Supplementation
Tryptophan is also available as a separate dietary supplement that can boost serotonin without interference from other amino acids. This is done so that people can treat insomnia, depression and mood problems, although the evidence for tryptophan as a potential treatment for these disorders is either mixed or tentative. A related form is a supplement known as 5-hydroxytryptophan, or 5-HTP, which is one of the intermediates between tryptophan and serotonin.
References
- Columbia University; Serotonin and Foods?; November 2009
- Medline Plus; Tryptophan; Linda Vorvick; February 2010
- "Pharmacological Reviews"; Precursor Control of Neurotransmitter Synthesis; RJ Wurtman, et al.; December 1980
- "Psychiatric News"; Depression-Serotonin Link: Many Mysteries Remain; Mark Moran; May 2003
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