Tryptophan (L-tryptophan) is an essential amino acid that must be supplied to the body with the diet. The most important neurotransmitters and neurohormones in the brain are formed from tryptophan, while its role is shown in the functioning of the nervous and immune systems. What is tryptophan responsible for in the body? Is its intake effective in depression? What are the best sources of tryptophan in food?
What is tryptophan? The role of tryptophan in the body
Tryptophan is one of the 20 protein amino acids found in the human body. It is one of the essential amino acids, which means that it must be supplied with the diet because the body does not produce it on its own. Like all amino acids, apart from glycine, tryptophan exists in the form of L-tryptophan and D-tryptophan. L-tryptophan is the biologically active form of tryptophan and it is the one that dominates in organisms, foods and supplements. Therefore, the names 'tryptophan' and 'L-tryptophan' are used interchangeably.
Tryptophan has the following functions in the body:
- it is a very important component of membrane proteins enabling them to anchor in cell membranes.
- It is a precursor of serotonin, one of the most important neurotransmitters, which affects mood, sense of well-being and falling asleep. Serotonin is commonly known as the hormone of happiness.
- It is the starting substrate for the production of melatonin - a neurohormone produced from serotonin which is connected with the circadian rhythm and falling asleep.
- 90% of tryptophan is metabolised to kynurenine (kynurenine), from which neuroactive central nervous system metabolites are formed. The kynurenine pathway of tryptophan catabolism is altered in several diseases, including psychiatric disorders such as schizophrenia, depression and bipolar affective disorder.
- Tryptophan is a precursor of niacin, a vitamin B3.
Tryptophan is not only metabolised by body cells, but also by the gut microbiome. Tryptophanase-producing bacteria convert tryptophan to indole and Clostridium sporogenes to 3-indolopropionic acid (IPA). IPA is a very strong neuroprotective antioxidant involved in the protection of the nervous system and brain against free radical damage as well as prevention of the brain from ischemia and Alzheimer's disease. Moreover, it participates in processes regulating the homeostasis of the intestinal mucosa and maintaining the tightness of the intestinal barrier. In turn, lactobacilli metabolize tryptophan to indole-3-aldehyde (I3A), which interacts with immune receptors in the gut and supports the immune system.
Recommended products with tryptophan
Effects of L-tryptophan deficiency
A deficiency of L-tryptophan manifests itself mainly in mood, memory and sleep disorders. It is caused by its function as a precursor of numerous substances necessary for proper brain function. Low levels of L-tryptophan in the body are mainly associated with a deficiency of serotonin and melatonin.
Research shows that people experiencing depression have lower levels of L-tryptophan than healthy people. In one of the experiments, 15 adults were exposed to stressors twice. The first time their blood tryptophan levels were normal, the second time their tryptophan levels were low. The researchers found that feelings of anxiety, tension and nervousness were higher when participants had low levels of L-tryptophan. Low levels of tryptophan are thought to intensify anxiety and fears, and may increase aggression and impulsivity in aggressive people, while high levels promote good social behaviour. L-tryptophan deficiency is associated with cognitive impairment, particularly memory decline. The greatest changes are seen in long-term memory, remembering events and experiences. Decreased levels of L-tryptophan are also associated with sleep problems.
Administration of L-tryptophan to research participants resulted in increased levels of both serotonin and melatonin among these individuals.
Body requirements for L-tryptophan
The body's requirement for L-tryptophan changes with age. It is the highest (per body weight) in infants and then decreases. Adults require 5 mg of L-tryptophan per kg of body weight per day.
The daily requirement for L-tryptophan is:
- up to 12 months of age - 13 mg/kg b.w,
- from 1 to 3 years of age - 8 mg/kg body weight,
- from 4 to 13 years of age - 6 mg/kg body weight,
- for boys from 14 to 18 years of age - 6 mg/kg body weight,
- for girls from 14 to 18 years of age - 5 mg/kg body weight,
- for girls from 14 to 18 years of age - 5 mg/kg body weight, for adults - 5 mg/ kg body weight.
L-tryptophan in relation with mood and depression - scientific opinions
L-tryptophan is the only precursor of serotonin. It has been shown many times that low levels of L-tryptophan in the body have a decreasing effect on serotonin levels. It is also known that tryptophan intake, either with the diet or in the form of supplements, increases serotonin levels, but not to the same extent in all individuals. The level of L-tryptophan conversion to serotonin is influenced by genetic factors and the gut microbiome.
Serotonin directly affects sleep, appetite as well as cognitive abilities - memory, attention, decision making, information processing, together with anxiety, fears, empathy, aggression and lowered mood. Low levels of serotonin in the brain are observed in depression. However, according to recent scientific opinion, the role of L-tryptophan in affecting mood and depression is not limited to serotonin production. Increasing tryptophan intake may improve mood through its role in the kynurenine pathway, inflammatory processes and melatonin production.
There is some evidence that L-tryptophan may reduce aggression in patients with schizophrenia and decrease argumentativeness while increasing agreeableness in healthy participants with a tendency to irritability or aggression.
L-tryptophan supplementation for mood disorders and depression has been used since the 1960s. Current scientific opinion is that tryptophan is more effective than placebo in mild to moderate depression, but it is not a first-choice therapy. Tryptophan can have a positive effect on mood, but you should not decide to take it in high doses (above your body's needs) without consulting your doctor. A medical examination and the opinion of a specialist are crucial in assessing your mental state and deciding whether the treatment is necessary.
Impact of tryptophan on sleep - scientific findings
Research involving humans shows that tryptophan has a positive effect on sleep quality. It was observed that increasing the amount of tryptophan in the diet prolongs sleep and improves its efficiency, shortens the time needed to fall asleep, reduces the number of awakenings during the night and the fragmentation of sleep. Such an effect was observed in people, who consumed additional products providing 60 mg of tryptophan for a week, and in another study, 70 mg of tryptophan for 19 days.
The dependence of sleep quality on the amount of tryptophan in the diet is a direct result of its effect on serotonin levels in the brain. Serotonin in turn produces melatonin which is key to falling asleep and circadian rhythm. Reducing the availability of tryptophan to the body lowers serotonin levels and subsequently reduces sleep quality. Studies have noted that reducing the amount of tryptophan supplied to the body or excluding it altogether results in a significant reduction in total sleep time, decreased sleep efficiency and time spent in the N2 sleep stage, which can be described as the stage of falling into a deep sleep. In contrast, the N1 phase - the transition period between wakefulness and sleep - is prolonged. In healthy people, N2 accounts for half of the total sleep time. Tryptophan deficiency is also responsible for the delay in the REM sleep phase, i.e. the dream phase, in which the functional regeneration of the brain takes place.
Other effects of tryptophan
The effects of tryptophan on mood and sleep disorders are the best studied. However, numerous studies look at other aspects of tryptophan's effects on the human body. It has been postulated that tryptophan may:
- support the fight against addictions,
- reduce headaches and migraines,
- reduce symptoms of premenstrual syndrome,
- reduce cravings for carbohydrate-rich foods,
- increase physical performance.
All these hypotheses require further research to confirm or rule out the effectiveness of tryptophan.
Tryptophan - sources in food
Tryptophan is one of the amino acids, that are less common in proteins. It makes up only 1-2% of all amino acids. However, this does not mean that it is found in food in too small amounts to meet the needs of healthy individuals. Without any problems with mood, sleep or immunity, it is enough to follow the rules of a healthy, balanced diet. Such a diet is a source of 900-1000 mg of tryptophan, whereas the tryptophan requirement of an adult is 5 mg/kg body weight. So, for example, a person who weighs 60 kg needs 300 mg of tryptophan, 80 kg - 400 mg, and 100 kg - 500 mg. Nevertheless, if you suspect yourself of having a tryptophan deficiency, live under stress or have noticed behavioural changes in yourself, you can reach for foods particularly rich in tryptophan more often to support an overstressed nervous system.
Foods rich in tryptophan are mainly meat, fish, eggs, pulses, seeds and nuts.
The best sources of tryptophan include:
- pumpkin seeds – 576 mg/100 g,
- mozzarella cheese – 571 mg/100 g,
- chicken and turkey meat – 400 mg/100 g,
- chia seeds – 380 mg/100 g,
- lean beef – 374 mg/100 g,
- lean pork – 368 mg/100 g,
- salmon – 335 mg/100 g,
- tuna – 335 mg/100 g,
- yellow cheese – 290 mg/100 g,
- flaxseed – 270 mg/100 g,
- Edamame beans – 242 mg/100 g,
- cashew nuts – 240 mg/100 g,
- tofu – 235 mg/100 g,
- peanuts – 210 mg/100 g,
- eggs – 153 mg/100 g,
- milk - 43-73 mg/100 g (the fattier the milk, the better the source of tryptophan),
- chocolate – 60 mg/100 g,
- oatmeal – 40 mg/100 g.
It is crucial to know that tryptophan is best absorbed from meals with a high glycemic index and load. Foods with a high protein content usually have a low or medium glycemic index/load, so to increase the availability of tryptophan, protein sources should be combined with rapidly digestible carbohydrates, e.g. meat with rice, pasta or potatoes; nuts with fruit; eggs with bread. In this way, the glycaemic load of the entire meal increases.
Based on data from the US National Health and Nutrition Examination Survey for nearly 30000 adults, dietary tryptophan intake was found to be inversely related to their reported depressive states and proportional to sleep duration. It means that even dietary amounts of tryptophan appear to provide mental health benefits.
Tryptophan in food supplements
Dietary supplements with tryptophan exist in capsule and powder form. Tryptophan in capsules is more convenient for lower doses, and when gram doses are necessary, tryptophan powder can be used. Tryptophan powder is suitable for dissolving for example in milk or fruit juice. The sugar content of these drinks has a positive effect on the absorption of tryptophan.
Research summaries published in 2021 in the Journal of Dietary Supplements and Nutrition Reviews suggest that:
- tryptophan supplementation may be effective in reducing anxiety and improving mood in healthy individuals.
- taking supplements with tryptophan may have a positive effect on sleep quality.
- the dosage of tryptophan for mood disorders that produced the desired effects ranged from 0.14 g to 3 g daily.
- the most effective doses of tryptophan in supplements for sleep problems were above 1 g daily.
Does tryptophan have side effects?
In scientific studies, participants were given tryptophan in doses up to 50 mg/kg body weight, which is 10 times more than the recommended intake. This dosage of tryptophan is considered to be safe. The only side effects observed included nausea, muscle tremors and dizziness, but similar symptoms were reported by those taking a placebo.
Tryptophan can be harmful to people who take antidepressants - selective serotonin reuptake inhibitors or MAO inhibitors. When these drugs are combined with tryptophan, it is possible to develop the so-called serotonin syndrome, which can include hyperthermia and coma. High doses of tryptophan may also cause fatigue and drowsiness.