L-tryptophan

Tryptophan is an essential amino acid that is abundant in food. Tryptophan is important as a building block of protein synthesis and for liver metabolism (1). In addition, tryptophan is required for the production of a number of important molecules that help transmit signals in the body. Tryptophan can be converted into a molecule known as 5-hydroxy-tryptophan - 5-HTP for short - which serves as a precursor for the production of serotonin and melatonin (2, 3). Serotonin is a neurotransmitter that affects multiple organs including the brain and digestive tract. In the brain, serotonin influences sleep, cognition and mood (4, 5). Melatonin, on the other hand, is a hormone that is significantly involved in the sleep-wake cycle (6). Tryptophan can be converted into niacin and thus contributes to a good niacin status in the tissues as well as to the biosynthesis of the coenzyme nicotinamide adenine dinucleotide (NAD). Approximately 60 mg tryptophan is equivalent to 1 mg niacin. Accordingly, niacin deficiencies only occur with a tryptophan-deficient diet. Tryptophan is also required for the formation of tryptamine (biogenic amine), which increases blood pressure.

All in all, tryptophan and the molecules it is needed to produce are essential for the body to function optimally.

The effects of tryptophan on mood, behavior and cognition

Although tryptophan has many functions, its effects on the brain are particularly noteworthy.

Low tryptophan levels are associated with mood disorders Several studies have shown that people suffering from depression may have lower than normal tryptophan levels (7, 8). Other studies have investigated the effects of changes in blood tryptophan levels. By lowering tryptophan levels, scientists can learn a lot about the functions of this amino acid. To achieve this, study participants consumed large amounts of amino acids - with or without tryptophan (9). In one such study, 15 adults were exposed twice to a stressful environment - once with normal blood tryptophan levels and once with low tryptophan levels (10). The scientists found that anxiety, tension and nervousness were higher when the subjects had low tryptophan levels.

Based on these results, low tryptophan levels could contribute to anxiety (11). They could also increase aggression and impulsivity in people prone to aggression (12). On the other hand, supplementation with tryptophan could promote good social behavior (13).

• Summary: Research shows that low tryptophan levels can contribute to mood disorders including depression and anxiety.

Low tryptophan levels may impair memory and learning ability

Changes in tryptophan levels can affect several aspects of cognition. One study found that lowering tryptophan levels worsened long-term memory performance compared to normal tryptophan levels (14). These effects were observed regardless of whether the subjects had a family history of depression. In addition, a large review concluded that low tryptophan levels impair cognition and memory (15). Memory performance in connection with experiences was particularly impaired. These results are probably based on the fact that serotonin production also decreases at lower tryptophan levels (15).

• Summary: Tryptophan is important for cognitive processes due to its role in serotonin production. Low levels of this amino acid can impair cognition, including memory for events and experiences.

Serotonin is responsible for many of the effects of tryptophan

In the body, tryptophan can be converted into the molecule 5-HTP, from which serotonin is subsequently formed (14, 16). Based on numerous studies, scientists agree that many of the effects of high or low tryptophan levels are based on its effects on serotonin or 5-HTP levels (15). In other words, an increase in tryptophan levels can also lead to an increase in 5-HTP and serotonin levels (17, 18). Serotonin and 5-HTP affect many processes in the brain and interference with their normal actions can have an impact on depression and anxiety (5). Many drugs developed to treat depression modify the action of serotonin in the brain and increase its activity (19). In addition, serotonin influences processes in the brain that are involved in learning (20). Treatment with 5-HTP can also help to increase serotonin levels and improve mood, alleviate panic disorders and treat insomnia (5, 21). All in all, the conversion of tryptophan to serotonin is responsible for many of its observed effects on mood and cognition (15).

• Summary: The important role of tryptophan is likely based on its role in serotonin production. Serotonin is essential for proper brain function and low tryptophan levels reduce the amounts of serotonin in the body.

The effects of tryptophan on melatonin and sleep

Once serotonin is produced in the body from tryptophan, it can be converted into another important molecule known as melatonin. Scientific research has shown that increasing tryptophan levels in the blood directly increases both serotonin and melatonin levels (17). In addition to being naturally occurring in the body, melatonin is also a popular supplement and can be found in several foods including tomatoes, strawberries and grapes (22). Melatonin influences the body's sleep-wake cycle. This cycle affects many other functions including the metabolism of nutrients and the function of the immune system (23). Several studies have shown that increasing the amount of tryptophan in the diet can improve sleep quality by increasing melatonin levels (24, 25). One study found that consuming tryptophan-enriched cereals for breakfast and dinner helped adults fall asleep faster and stay asleep longer than those who ate regular cereals (25). Symptoms of anxiety and depression were also reduced and it is likely that the tryptophan helped to increase both serotonin and melatonin levels.

Other studies have also shown that taking melatonin as a supplement can improve sleep quantity and quality (26, 27).

• Summary: Melatonin is important for the body's sleep-wake cycle. Increased tryptophan intake can lead to higher melatonin levels and increase both sleep quantity and quality.

Sources of tryptophan

Many different protein-rich foods are good sources of tryptophan (28). For this reason, every time you eat protein, you also consume some tryptophan. Your tryptophan intake depends on how much protein you eat and which protein sources you eat.

Some foods are particularly rich in tryptophan. These include poultry, crab and eggs (28). Lactalbumin, the water-soluble part of whey protein, is particularly rich in this amino acid and also contains a lot of tryptophan. Tryptophan is therefore abundant in milk and dairy products. This amino acid is quickly broken down through contact with oxygen. It is therefore lost or its content is reduced during many processing operations in the food industry.

It is estimated that the typical diet provides about 1 gram of tryptophan per day (29). Tryptophan or one of the molecules produced from tryptophan - such as 5-HTP or melatonin - can also be taken as a supplement.

• Summary: Tryptophan is found in foods containing protein and in supplements.

When tryptophan is lacking in the body

A lack of tryptophan can lead to Hartnup syndrome, in which amino acids are increasingly excreted. The disease leads to pellagra-like symptoms (light dermatoses due to malabsorption of tryptophan). Skin diseases, disorders of the central nervous system and depression can also develop, depending on the serotonin deficiency.

Typical groups that have an increased need for tryptophan

• Athletes
• possibly with sleep disorders and depression

The correct use of tryptophan supplements

If you want to improve your sleep quality and well-being, you can consider using a tryptophan supplement. However, you also have some other options. For example, you can choose supplements that contain molecules made from tryptophan. These include 5-HTP and melatonin, among others. If you use tryptophan itself, apart from serotonin and melatonin production, it can also be used in other body processes such as the production of protein or niacin. This is why supplementing with 5-HTP or melatonin may be a better choice for some people (5). Those looking to improve mood and cognitive function might opt to use tryptophan or 5-HTP. Both of these compounds can increase serotonin levels, with 5-HTP being able to convert to serotonin faster than tryptophan (5). In addition, 5-HTP may also have other effects such as reducing food intake and body weight (30, 31).

Dosages of 5-HTP range from 100 to 900 mg per day (31).

For those interested in promoting sleep, supplementation with melatonin may be the best choice (27). Dosages of 0.5 to 5 mg per day have been used, with 2 mg likely to be the most widely used dosage (32). For those who wish to use tryptophan themselves, it should be noted that doses of up to 5 grams per day have been used in studies (29).

• Summary: Tryptophan or its products (5-HTP and melatonin) can be taken as a dietary supplement. The best choice depends on the symptoms you are targeting.

Side effects

As tryptophan is an amino acid that occurs naturally in many foods, it can be assumed that tryptophan is safe and harmless in normal amounts. It is estimated that the typical diet provides about 1 gram of tryptophan per day, with some people supplementing with dosages of up to 5 grams per day (29). The potential side effects of tryptophan have been studied for over 50 years, but few have been reported. Occasional side effects include nausea and dizziness, which have been reported at doses above 50 mg per kilogram of body weight, or 3.4 grams for a 68-kilogram adult (29). These side effects may be more pronounced when tryptophan or 5-HTP are taken with medications such as antidepressants that can affect serotonin levels. If the activity of serotonin is excessively increased, this can result in a condition called serotonin syndrome (33). This can include several symptoms including sweating, tremors, agitation and delirium (29),

In the 1980s, it was suspected that the administration of tryptophan was associated with eosinophilic myalgia syndrome. Studies did not confirm this suspicion. The cases in question were probably due to impurities in a single tryptophan preparation during manufacture. Since 1996, tryptophan has therefore been approved again as a medicinal product in Germany. If MAO inhibitors are taken for depression, tryptophan should not be used. Athletes should avoid high doses of tryptophan, in the region of over 3 grams per day. Excessive doses can alter blood counts and lead to muscle pain and fatigue. If you are using any medication that affects your serotonin levels, you should consult your doctor before taking tryptophan or 5-HTP. Summary: Studies conducted with tryptophan supplements report only minimal side effects. However, nausea and dizziness may occasionally occur at high doses. However, when combined with medications that affect serotonin levels, more serious side effects may occur.

Conclusion

Your body uses tryptophan to produce several important molecules including serotonin and melatonin. Serotonin affects your mood, cognition and behavior, while melatonin affects your sleep-wake cycle. Thus, low tryptophan levels can result in reduced serotonin and melatonin levels, which can have devastating effects.

Although tryptophan is found in protein foods, it is often taken as a dietary supplement. Tryptophan is probably safe and harmless in moderate doses. Occasionally, however, side effects can occur. These side effects can be more serious if you are taking medications such as antidepressants that affect your serotonin levels. Several other molecules that are produced in the body from tryptophan are also available as supplements. These include melatonin and 5-HTP.

All in all, tryptophan is a very important amino acid for health and well-being. Certain groups of people may benefit from increasing their intake of tryptophan or the molecules that are made from tryptophan.

References

1. https://www.ncbi.nlm.nih.gov/pubmed/19301095
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4283270/
3. https://www.ncbi.nlm.nih.gov/pubmed/23388477
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8. http://www.sciencedirect.com./science/article/pii/0165032789900517
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13. https://www.ncbi.nlm.nih.gov/pubmed/26987640
14. https://www.ncbi.nlm.nih.gov/pubmed/10090643
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16. https://www.ncbi.nlm.nih.gov/pubmed/26805875
17. https://www.ncbi.nlm.nih.gov/pubmed/2011617
18. https://www.ncbi.nlm.nih.gov/pubmed/17222434
19. https://www.ncbi.nlm.nih.gov/pubmed/25969470
20. http://www.sciencedirect.com/science/article/pii/S0149763499000676
21. https://www.ncbi.nlm.nih.gov/pubmed/12559480
22. https://www.ncbi.nlm.nih.gov/pubmed/20536683
23. https://www.ncbi.nlm.nih.gov/pubmed/25908646
24. https://www.ncbi.nlm.nih.gov/pubmed/25407790
25. https://www.ncbi.nlm.nih.gov/pubmed/22622709
26. https://www.ncbi.nlm.nih.gov/pubmed/18036082
27. https://www.ncbi.nlm.nih.gov/pubmed/19584739
28. http://nutritiondata.self.com/foods-000079000000000000000.htm
29. https://www.ncbi.nlm.nih.gov/pubmed/23077193
30. https://www.ncbi.nlm.nih.gov/pubmed/9705024
31. https://www.ncbi.nlm.nih.gov/pubmed/1384305
32. https://www.ncbi.nlm.nih.gov/pubmed/21845053
33. https://www.ncbi.nlm.nih.gov/pubmed/24004848