Tryptophan is an amino acid that produces serotonin, melatonin, and kynurenine. Supplementation may help with sleep quality, mental health, and PMS. However, there are important safety concerns and limitations. Read on to learn the benefits, food sources, and side effects of tryptophan. What is Tryptophan?
Tryptophan is one of the 8 essential amino acids, meaning it is vital but cannot be produced by the body. Hence, tryptophan must be supplied from dietary sources [ 1 ].
L-tryptophan is the natural version of the amino acid and a building block of protein in the body.
In humans, tryptophan is not stored for long periods and therefore has the lowest concentration in the body among all the amino acids. However, only small amounts of tryptophan are required [ 1 ]. Foods
Common foods that contain tryptophan include oats, bananas, dried prunes, milk, tuna fish, cheese, bread, chicken, turkey, peanuts, and chocolate [ 1 ]. Why Is It Important?
Tryptophan is converted to 5-hydroxytryptophan ( 5-HTP ) in the brain, which produces serotonin [ 2 , 3 ].
Tryptophan absorption into the brain is influenced by diet.
A high carbohydrate, low protein diet will release insulin , which ultimately increases the absorption of tryptophan into the brain and can, therefore, increase serotonin. This is the mechanism by which eating carbs may increase serotonin [ 4 ].
BCAAs compete with tryptophan absorption into the brain. Eating a high protein diet (high BCAAs) will cause less tryptophan to enter the brain, thus reducing serotonin levels [ 4 ].
However, higher protein diets usually have higher tryptophan, which can cancel out the effect from the BCAAs. Health Benefits
1) Sleep Quality and Insomnia
Tryptophan produces melatonin in the brain (pineal gland), the gut, the retina, and immune cells. Melatonin regulates the circadian rhythm and sleep patterns and is used as a supplement itself to help people sleep [ 5 , 6 ].
A study of 5 healthy volunteers showed that L-tryptophan supplementation increased average total sleep. All of them noticed some form of drowsiness a half hour before sleep [ 7 ].
In a study on 7 insomniac patients, L-tryptophan supplementation increased total sleep (by 28%). The supplementation also decreased early-morning wakefulness by an average of 37 minutes [ 7 ].
Tryptophan supplementation even helped induce sleep in manic patients. A study of 10 patients with mania showed improvements in total sleep after L-tryptophan supplementation [ 8 ].
In a dose-response study of 15 insomniac patients, L-tryptophan (250 mg) increased stage 4 sleep (deep sleep). Normal dietary intake is usually around ½-1 gram of L-tryptophan, so even minimal amounts may increase deep sleep [ 9 ].
Tryptophan supplementation may also improve obstructive sleep apnea (airflow blockage during sleep). A study of 12 patients showed that L-tryptophan supplementation increased sleep in those with obstructive sleep apnea during non-REM sleep. However, patients with central sleep apnea showed no improvements [ 10 ].
The above findings stem from small clinical trials and thus require further investigation. 2) PMS
The breakdown of tryptophan via the kynurenine pathway is affected by the phase of the menstrual cycle, which can also indirectly affect serotonin production. After ingesting tryptophan, kynurenine was 40% higher during the luteal phase than in the follicular phase [ 11 ].
In a study of 37 patients, L-tryptophan supplementation (6 g daily) improved the following symptoms in women suffering from premenstrual dysphoria (a severe type of PMS ) [ 12 ] :
Mood improved by 34.5% in those given L-tryptophan supplements. 3) Smoking Cessation
A study of 16 people trying to quit smoking showed that L-tryptophan and a high-carbohydrate diet along with regular smoke-ceasing therapies decreased anxiety and withdrawal symptoms. People given tryptophan supplements smoked fewer cigarettes compared to placebo. Further research is warranted [ 13 ].
No valid clinical evidence supports the use of grape seed extract for any of the conditions in this section. Below is a summary of up-to-date animal studies, cell-based research, or low-quality clinical trials which should spark further investigation. However, you shouldn’t interpret them as supportive of any health benefit. 4) Depression
Many depressed patients also suffer from insomnia and other sleep-depriving conditions. Therefore, tryptophan’s ability to help with insomnia could aid these depressed patients [ 14 , 9 ].
A randomized study of 25 young adults showed that high tryptophan diets increased mood and decreased depressive symptoms and anxiety [ 15 ].
In a study of 24 patients, clomipramine (a drug for depression) and L-tryptophan were more effective in improving depressed mood, suicidal intent, and anxiety compared to clomipramine alone [ 16 ].A meta-analysis of tryptophan’s effects on depression confirmed some positive effects, but the authors underlined the low evidence quality (only two trials included) and avoided making conclusions [ 17 ].A study of 6 depressed patients showed that L-tryptophan supplementation did not help and the patients needed further treatment before release [ 18 ].Depressed patients often have problems creating serotonin from tryptophan. Instead, they create other metabolites such as quinolinic acid, which can be toxic. For these patients, tryptophan supplementation may not help [ 19 ].When tryptophan is converted to kynurenine and not serotonin, depression may worsen. Some kynurenine metabolites are toxic and animal models have shown increased depressive symptoms with increased kynurenine [ 20 ]. Due to low-quality evidence and some conflicting results, further trials should clear up the potential benefits of tryptophan for depressive disorders. 5) Mania In a small study of five patients with mania, L-tryptophan supplementation improved the treatment with chlorpromazine hydrochloride (CPZ) and reduced side effects [ 21 ].In 24 patients with acute mania, L-tryptophan supplementation decreased manic symptoms by 43% outperforming a previous treatment with lithium (41%). Those who stopped receiving tryptophan showed worsening of the symptoms [ 22 ].However, in a clinical trial done on 10 female mania patients, the L-tryptophan supplementation did not perform better than placebo [ 23 ]. More studies are needed to clear out these conflicting results. 6) Appetite Reduction In a study of 15 healthy volunteers, those receiving L-tryptophan supplementation ate […]