Tryptophan is an amino acid used to build proteins. It is considered essential because the human body cannot produce it and must obtain it from dietary sources. This compound helps create and maintain the body’s proteins, muscles, and enzymes.
The Role of Tryptophan in the Body
Once absorbed from food, tryptophan becomes a precursor for several important molecules. A portion of dietary tryptophan is used for serotonin synthesis within the brain. This process involves converting tryptophan into 5-hydroxytryptophan (5-HTP), which is then changed into serotonin, a neurotransmitter that helps regulate mood, sleep, and appetite.
The body also uses serotonin to produce melatonin, a hormone that manages the sleep-wake cycle. This conversion primarily occurs in the pineal gland, a small gland in the brain, and its activity increases in response to darkness. The synthesis of both serotonin and melatonin demonstrates how this amino acid influences daily patterns of mood and rest.
Beyond its role in the brain, the liver can convert tryptophan into niacin, also known as vitamin B3. This pathway is important when dietary niacin intake is low, as it helps prevent deficiency. Niacin contributes to energy metabolism and nervous system function. For this conversion to happen, the body requires sufficient levels of iron, riboflavin, and vitamin B6.
Dietary Sources of Tryptophan
Tryptophan is present in most protein-based foods. It is found in poultry like chicken and turkey, red meat, fish, and eggs. Dairy products such as cheese and milk are also reliable sources, along with plant-based options like nuts, seeds, soybeans, and oats.
A common belief suggests that the tryptophan in turkey is the cause of sleepiness after a large Thanksgiving meal. While turkey does contain this amino acid, its levels are comparable to those in many other meats. Foods like cheese and soybeans actually contain more tryptophan per gram than turkey does.
The true cause of sleepiness after a holiday feast is often the large quantity of carbohydrates consumed. Foods like mashed potatoes and desserts cause a rapid increase in blood sugar, triggering a release of insulin. This insulin helps clear other amino acids from the bloodstream, leaving tryptophan with less competition to cross the blood-brain barrier. This leads to increased serotonin production in the brain and a feeling of lethargy.
Understanding Tryptophan Supplements
Some people take L-tryptophan, the form found in supplements, to address issues like insomnia, anxiety, or depression. The theory is that increasing tryptophan levels boosts serotonin production, potentially improving mood and sleep. However, scientific evidence for its effectiveness is mixed and it is not a consistently reliable treatment for depression.
Mild side effects can occur with supplement use, including drowsiness, stomach pain, and nausea, and are more common at higher doses. A safety concern arose in 1989 with an outbreak of Eosinophilia-myalgia syndrome (EMS), a serious condition linked to contaminated L-tryptophan supplements. Investigations traced the outbreak to a single manufacturer, suggesting the contaminant, not tryptophan itself, was the cause.
The most serious risk with L-tryptophan supplements is the potential for drug interactions, particularly with antidepressants. Combining L-tryptophan with medications like SSRIs or MAOIs can lead to a dangerous condition called serotonin syndrome. This syndrome results from excessive serotonin activity in the brain and can cause symptoms such as agitation, rapid heart rate, high body temperature, and delirium.