What is Tryptophan?

Tryptophan is one of the 22 amino acids needed for protein synthesis and healthy functioning of the human body. Abbreviated as W or Trp, tryptophan is an essential amino acid and must be source from foods. One distinctive structural aspect of this amino acid is that it incorporates an indole functional group. Indole is an aromatic organic compound frequently used in fragrances and within pharmaceuticals.

The Role of Tryptophan

neural regulationIn addition to the synthesis of proteins, tryptophan has a variety of specialised functions. This amino acid is the precursor to serotonin. This monoamine neurotransmitter is mainly concentrated within the gastrointestinal tract in enterochromaffin cells, and subsequently within blood platelets. Here it helps to regulate blood clotting and hemostasis. Serotonin is also synthesised in the central nervous system in serotonergic neurons. Here it has a range of functions including regulating mood, sleep, appetite, as well as cognitive function such as learning and memory.

In addition to manufacturing serotonin, tryptophan is needed to synthesis the vitamin niacin (B3) from quinolinic and kynurenine acids. Niacin is a water soluble vitamin that helps to lower cholesterol and convert certain foods into energy. This vitamin is also needed to maintain a healthy digestive system and central nervous system, as well as to nourish and protect the skin. Niacin is also required for production of red blood cells and the synthesis of hormones such as oestrogen, testosterone and progesterone.

Tryptophan has been well research over the years and is known to been an effective amino acid for treating a range of health issues. Some of the common applications for tryptophan are outlined below.

As tryptophan is a precursor to serotonin it has an important role in preventing and treating depression. Researchers have investigated the potential for tryptophan to act as an effective antidepressant. One study conducted over a 12 week period and involving 115 patients found that tryptophan significantly decreased the symptoms of depression1.

In addition to acting as an effective antidepressant in itself, tryptophan appears to also enhance the effects of some other antidepressant medications. Results from one study show that patients being treated for severe depressive disorders using the drug fluoxentine had a significant reduction in symptoms after one week when also given 2 to 5 grams of tryptophan daily2.

depressionThe mood disorder known as SAD affects people that are otherwise unaffected by mental health problems. The depressive symptoms associated with SAD are common during winter months and are reoccurring each year. A study conducted at the University of British Columbia used tryptophan to treat SAD patients. Each patient took 3 grams of the amino acid daily for a period of three weeks and the results showed a significant reduction in the mean depression scores3.

Premenstrual dysphoria is a severe disorder in which women experience irritability, tension and extremely debilitating depressive symptoms. A study conducted in Montreal at the St. Mary’s Hospital treated premenstrual dysphoric disorder patients with 6 grams of tryptophan and found that the amino acid significantly reduced the symptoms of depression4.

tryptophan sleeping aid
Tryptophan supplements are often used as a sleeping aid. Research has shown that approximately 1 gram of tryptophan can help to stimulate sleepiness and make it easier for patients to fall asleep5. It was noted that patients with mild insomnia responded better than those with more chronic conditions. One of the key triggers for sleep is the hormone melatonin. This hormone helps to regulate the body’s circadian rhythm and stimulate drowsiness. Melatonin is synthesised from serotonin. Hence, tryptophan is required to produce melatonin and maintain healthy circadian rhythms.

There is a correlation between serotonin and weight loss. Serotonin helps to suppress appetite and regulate metabolism. Also, because serotonin elevates the mood, individuals are more emotionally stable and this can help reduce food cravings and incidences of binge eating.

Health Problems Associated with Tryptophan Deficiencies

Most of the health concerns associated with tryptophan deficiencies related to niacin. When the body is mildly lacking in niacin, individuals can experience a range of symptoms including fatigue, depression, vomiting, canker sores and indigestion. A severe deficiency can cause a disease known as pellagra. Common symptoms of pellagra include dementia, emotional disturbances, insomnia and dermatitis. If left untreated, pellagra can lead to death within four to five years. Pellagra was once a common disease. Today, pellagra is largely restricted to impoverished populations in countries such as Africa, North Korea, Indonesia and China.

Tryptophan Rich Foods

To ensure that the body is able to synthesis serotonin and niacin, it’s important to include foods rich in tryptophan in your diet. Good sources of this essential amino acid include poultry, eggs, cheese, fish, milk, peanuts, pumpkin seeds, sesame seeds, tofu, soy, lentils, collard greens, mustard greens, broccoli, kale, cauliflower, Brussels sprouts and beans. Also, in order for niacin to be produced from tryptophan, the body needs to have an adequate supply of iron (Fe), vitamin B6 and riboflavin.

Food % Protein L-tryptophan % of Protein
Soybeans 36.5 % 590 mg 1.6 %
Peas (dried) 24.6 % 266 mg 1.1 %
Chicken breast (raw) 21,2 % 267 mg 1.3 %
Pork (raw) 21.0 % 220 mg 1.1 %
Salmon (raw) 20.4 % 209 mg 1.0 %
Cocoa powder (without sugar) 19.6 % 293 mg 1.5 %
Cashew nuts 18.2 % 287 mg 1.6 %
Walnuts 15.2 % 170 mg 1.1 %
Oats 13.2 % 182 mg 1.4 %
Chicken egg 12.6 % 167 mg 1.3 %
Brown rice 7.9 % 101 mg 1.3 %
Corn flour 6.9 g 49 mg 0.7 %
Cow’s milk (3.8% fat) 3.3 g 46 mg 1.4 %


Tryptophan is an essential amino acid important for the synthesis of the vitamin niacin and the hormone serotonin. It is also indirectly required to manufacture melatonin to regulate circadian rhythms. Through providing the body with adequate concentrations of tryptophan it’s possible to prevent and treat depressive disorders and safeguard against more serious mental illnesses. Tryptophan can also be used to help treat mild insomnia and promote weight loss through supporting a better metabolism.

A balanced diet of tryptophan-rich foods will provide the body with the necessary concentration of this amino acid. There are also dietary supplements available that contain tryptophan to help promote well-being. However, it’s important to seek medical advice prior to taking tryptophan supplements if you have any underlying health concerns.

Related studies:

  1. “http://www.ncbi.nlm.nih.gov/pubmed/7156248”
  2. “http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1407729/?tool=pmcentrez”
  3. “http://www.ncbi.nlm.nih.gov/pubmed/9114947”
  4. “http://www.ncbi.nlm.nih.gov/pubmed/10023508”
  5. “http://www.ncbi.nlm.nih.gov/pubmed/6764927”