Sleep is a crucial physiological state where the body is in a relaxed state, allowing the body and mind to rest. However, many people have experienced insomnia, and there are various folk remedies and traditional methods claimed to help with falling asleep. Yet, most of these lack scientific evidence to support their effectiveness. Today, we’ll introduce tryptophan, which has substantial scientific evidence supporting its role in aiding sleep. Let’s delve into the functions of tryptophan!
What is Tryptophan?
Tryptophan is an essential amino acid that the body cannot synthesize on its own and must be obtained through external sources. It has the highest molecular weight among all natural amino acids. Its primary absorption site is in the small intestine. After entering the bloodstream, it can be transported with the assistance of albumin. When it reaches the tissues that require tryptophan, it competes for binding sites with large neutral amino acids (LNAA) and enters cells. Once inside cells, tryptophan primarily undergoes three metabolic pathways:
The first pathway is the kynurenine pathway, where tryptophan can generate vitamin B3 (niacin) and its derivatives (NAD+, NADH, etc.). This pathway also produces metabolites such as kynurenine acid and quinolinic acid, which are associated with neurological and immune functions. The second pathway is the serotonin pathway, which produces two well-studied neurotransmitters, serotonin and melatonin. The third pathway involves the interaction of tryptophan with gut bacteria in the gastrointestinal tract, leading to the production of indole and related metabolites through the indole pathway[1].
What are the effects of Tryptophan?
Early clinical research has found that individuals who lack tryptophan in their diet are more likely to experience physiological, psychological, and behavioral abnormalities. These may include symptoms such as motion sickness, visual discrimination issues, cognitive impairment, memory deficits, poor social skills, emotional instability, and sleep disorders[2]. Currently, research on the functions of tryptophan has yielded significant results in the fields of cognition, emotions, and sleep, as well as immune regulation.
Cognition:
Supplementing with tryptophan can aid in long-term memory for language and abstract information and help improve concentration. However, consuming higher doses of tryptophan can have a sedative effect, impacting psychological actions such as reflex actions (withdrawal response to a needle) and skill-based actions (cycling or playing the piano)[3].
Emotions:
Tryptophan supplementation has an antidepressant effect, alleviates premenstrual mood discomfort, and enhances emotional regulation abilities. This effect is more pronounced in individuals under psychological stress[3].
Social Behavior:
Increased brain serotonin levels are positively correlated with social behavior. Conversely, lower serotonin levels are associated with aggression, violent crime, and antisocial personality. Tryptophan supplementation can enhance positive social behaviors, such as friendliness, sharing, helping others, and generosity[4].
Sleep:
Sleep disorders encompass difficulties with falling asleep (insomnia), as well as overall reduced sleep time, fragmented sleep, and wakefulness during sleep. The sleep cycle consists of four stages, including three non-rapid eye movement (NREM) stages and one rapid eye movement (REM) stage. Tryptophan supplementation can enhance the chances of plasma tryptophan crossing the blood-brain barrier (BBB) and being converted into melatonin by the pineal body in the brain, thereby improving sleep quality. Clinical studies have found that tryptophan supplementation can increase total sleep time, shorten the time it takes to fall asleep, and enhance both NREM and REM sleep, thus improving overall sleep quality[5].
Immune Regulation:
Enzyme activities of the kynurenine pathway are present in many immune cells. During viral infections, parasitic infections, or inflammatory states, the body consumes large amounts of tryptophan and increases related metabolites in the kynurenine pathway. Additionally, B cells and T cells have serotonin receptors on their surfaces, and serotonin is an essential signaling molecule for immune cell proliferation. It also plays a role in regulating the secretion of cell hormones[6].
Further reading: Comparison of 7 Commercially Available Sleep Aids – Melatonin and GABA Recommendations (Sesame May Not Be the Best!)
Which foods contain tryptophan?
Some dry goods products contain high levels of tryptophan, such as red beans (dried weight), powdered milk, cheese powder, dried fish, seeds, and nuts. However, the individual serving sizes of dry goods are relatively small, so the total intake of tryptophan may not be necessarily high. Moreover, there might be concerns about consuming additives and excessive sodium from such products. Other foods with high tryptophan content can be obtained from sources like meat, edamame, tofu, and eggs.
When is the best time to consume tryptophan?
Foods with high protein content generally also contain more tryptophan, but due to its larger molecular weight, tryptophan’s proportion relative to other amino acids is lower. Additionally, tryptophan competes with other large neutral amino acids (LNAA) for cellular entry. Therefore, when supplementing with tryptophan, it’s advisable to avoid consuming high-protein foods simultaneously. Furthermore, after a high carbohydrate intake, insulin secretion increases, stimulating muscle protein synthesis. During this process, amino acids other than tryptophan become the preferred raw materials for muscle protein synthesis, leading to a relative increase in plasma tryptophan concentration. Hence, the optimal time to supplement tryptophan is after consuming carbohydrate-rich foods[7].
Are there side effects of consuming too much tryptophan?
Excessive tryptophan can increase the production and release of serotonin in the intestines, leading to increased intestinal motility and causing diarrhea. An excess of serotonin can also stimulate the vagus nerve, resulting in symptoms like nausea and vomiting. In clinical studies, even at doses as high as 15 grams of tryptophan, acute or chronic symptoms are rare. However, one study found that supplementation with 7.5 grams of tryptophan led to symptoms like nausea and vomiting in some participants[8]. Caution should be exercised when evaluating three groups: pregnant or breastfeeding individuals, those with impaired liver or kidney function, and patients taking central nervous system medications. Consultation with a medical professional is recommended in these cases.
Tryptophan is an essential amino acid important for the human body. Many animal-based products also contain it. To maximize the benefits of tryptophan, besides considering dosage, it’s essential to carefully choose the timing of supplementation. By using tryptophan correctly, you can enhance the quality of your sleep and relaxation.
