L-TRYPTOPHAN & 5-HTP

Written by Slawomir (“Swavak”) Gromadzki, MPH

HEALTH BENEFITS

SEROTONIN & MOOD

A very important way of increasing serotonin level in our body is diet rich in amino acid tryptophan which is converted to serotonin in the brain. Dr Agatha Thrash in her book “Food Allergies” states that, “Foods with low content of tryptophan may negatively affect the levels of serotonin thus leading to depression”. According to the study published in the Archives of General Psychiatry, women with a history of bulimia nervosa experienced relapses of this eating disorder as a result of consuming an amino acid mixture which was deprived of tryptophan.

According to Dr. Michael Greger, “Prozac appears to work by boosting serotonin levels but it can cause significant side effects. How about using foods high in serotonin, such as plantains, pineapples, bananas, kiwis, plums, and tomatoes. Plants contain dopamine, serotonin, and melatonin at concentrations high enough to actually alter levels in our bloodstream. We don’t need serotonin in our blood, though; we need it in our brain. Serotonin can’t cross the blood-brain barrier, but the precursor to serotonin can. This precursor is an amino acid called tryptophan that we get from our diet. When people think tryptophan, they think Thanksgiving turkey, but researchers at MIT dispelled those myths about a decade ago. Tryptophan is one amino acid among many found in turkey (or meat and dairy) proteins, and they compete with one another for transport across the blood-brain barrier into the brain. Since tryptophan is present in most animal proteins in relatively small quantities it gets muscled out of the way. When we eat plant foods, though, the carbohydrates trigger a release of insulin that causes our muscles to take up many of the non-tryptophan amino acids as fuel, potentially leaving our tryptophan first in line for brain access. Animal foods can even make things worse. In the experiment, those given a turkey/egg/cheese breakfast experienced a drop in tryptophan levels, whereas those given a waffle/orange juice breakfast saw their levels rise.”

DEPRESSION

In some clinical studies, 5-HTP was found to alleviate depression [>].

The antidepressant effects of 5-HTP have been comparable to those of some conventional antidepressants [>]. However, the combined use of 5-HTP together with SSRIs have strong synergistic effects on serotonin levels. For this reason, some researchers have investigated the use of 5-HTP in combination with SSRIs [>, >, >]. In a clinical trial involving 52 healthy subjects, 5-HTP and an SSRI enhanced serotonin levels by 35% and 100%, respectively. When both were administered together, however, they increased serotonin by 500% [>].

PANIC ATTACKS & ANXIETY

24 people subjects who suffered from chronic panic attacks, due to lower serotonin levels in the brain, found significant relief as a result of taking a daily dose of 200 mg of 5-HTP [>].

In a study involving young adults with signs of chronic stress and/or anxiety, 6-weeks of supplementation with 5-HTP decreased anxiety by 3 weeks. According to the authors, the positive effect was the result of increased BDNF (Brain-Derived Neurotrophic Factor) and serotonin levels [>].

In clinical trials, 5-HTP was shown to increase GABA levels, thus promoting a sense of relaxation and decreased anxiety [>].

APPETITE

When humans and animals are fed tryptophan-free diets, appetite is significantly increased, resulting in binge eating. A diet which is low in tryptophan leads to serotonin deficiency because our brain interprets lack of tryptophan as a result of starvation and therefore it stimulates the appetite. This stimulation results in a preference for carbohydrates and craving for sweet foods. Unfortunately, most people choose products high in refined sugar instead of complex carbohydrates (fresh and dried fruits).

MIGRAINES

Apart from 5-HTP (Tryptophan) also Vitamin B2 supplementation has proved to be often beneficial in coping with migraine headaches. Riboflavin is a safe and well-tolerated approach in treating migraine headaches (>). It also reduced the frequency of migraines (>, >).

SLEEP

Low melatonin levels have been linked to insomnia. Melatonin is produced from serotonin – our feel-good hormone – which in turn is derived from tryptophan – an amino acid found in food. Thus biochemical pathway is Tryptophan —> Serotonin —> Melatonin.

Medical research indicates that taking tryptophan before bedtime can help trigger sleepiness and delay wake times. Specialists believe tryptophan brings on sleep by boosting levels of serotonin, a body chemical that promotes relaxation. However, consumers should take this supplement with caution as it may adversely interact with certain antidepressants, including selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), and others.

DREAMMING AFTER TAKING 5-HTP

Many people have reported that taking 5-HTP increases dream vividness. This effect isn’t surprising, as research has linked increased serotonin levels with dream vividness. Edward Pace-Schott reported that subjects on SSRIs (serotonin reuptake inhibitors) dream much longer reports than normal, and experience more lucid or bizarre dreams. In the first part of the night, 5-HTP causes a REM suppression while promoting deep sleep. REM suppression leads to REM rebound in the second half the night. Cannabis and alcohol have a similar effect on dreams.

Serotonin helps in regulating deep sleep. By increasing serotonin levels, 5-HTP can help to prolong deep sleep cycles during the first part of the night. The brain then realizes that it does not need anymore deep sleep and gives you what is referred to as a “REM rebound”, which is extra long REM cycles during the second half of the night. Since most lucid dreams occur during REM sleep, this makes having a lucid dream much easier because of the increased time spent in REM. For this reason, advanced lucid dreamers love to use 5-HTP for lucid dreaming

EXERCISE (ATHLETIC, SPORTS) PERFORMANCE

According to an experiment with 20 participants, a dose of 300 mg of L-tryptophan twice a day for 3 days, improved their power output during the last 20 minutes of exercise [>].

In a study involving twelve sportsmen, those given L-tryptophan supplements had their total exercise time improved by 50% [>].

Tryptophan was found to lower the athletes’ perceived exertion (way to quantify training load combined with GPS loading), most likely due to the increased pain tolerance [>].

FACTORS THAT LEAD TO TRYPTOPHAN DEFICIENCY

FOOD SOURCES OF TRYPTOPHAN

All the following plant foods are either excellent sources of this important amino acid or effectively help our body to produce it: Tofu (soya cheese), all pulses or legumes (beans, chickpeas, lentils, etc.), Spirulina, brown rice, avocados, oats, tomatoes, kiwis, plums, fresh pineapples, eggplant, bananas, seeds and nuts (especially sesame seeds, pumpkin seeds, peanuts, sunflower seeds, and walnuts), dried fruits (raisins, dates, figs). Also, chia seeds, that are known to be the best source of omega 3, contain more than twice the amount of tryptophan found in turkey, which means they are very helpful in increasing the levels of serotonin in our body.

TRYPTOPHAN IN PLANT VS ANIMAL FOODS

It is true that tryptophan is also found in animal foods especially milk, but animal sources (including milk and dairy) are much higher in other competitive amino acids thus hindering the absorption of tryptophan. In addition, milk also contains numerous high-risk factors such as cholesterol, triglycerides, antibiotics, dioxins and may be contaminated with extremely dangerous and deadly prions or leukaemia virus which are able to survive the pasteurization and cooking process.

Because tryptophan is an amino acid (protein), therefore a diet rich in other types of protein (meat and dairy products) greatly hinders tryptophan from passing from the blood to your brain. It is so because tryptophan has to compete with many other amino acids (proteins) while trying to enter the brain and as a result, only a small amount of this important amino acid gets in. That is another reason why you should be on the plant-based and unrefined diet. It is not only rich in tryptophan, which is essential to produce serotonin, but at the same time, unlike the animal-based diet, it is not too high in protein, and also gives you the opportunity to eat unrefined sweet carbohydrates which are necessary to allow tryptophan to reach the brain where it is converted to serotonin thus helping you to control appetite and negative emotions.

There is a myth that plant protein does not contain significant amounts of tryptophan. The opposite is true as tryptophan is present in almost all forms of plant protein. The highest amount of tryptophan is found in cooked soya beans and Tofu (soya cheese). Another excellent source is Tahini (sesame butter) and Halva which is very tasty and sweet. Apart from ground sesame seeds, Halva may contain different sweeteners such as honey or sugar. However, in health food shops you can also find Halva sweetened with grape juice, which seems to be a better choice. Although Tahini and Halva are not higher in tryptophan as soya beans and Tofu yet the ratio between tryptophan and other amino acids found in these two products is most beneficial and for this reason, they are regarded as one of the best sources of tryptophan.

5-HTP (TRYPTOPHAN) – THE BEST SUPPLEMENTAL FORM OF TRYPTOPHAN

Fortunately, there are some simple means which are helpful and effective in raising brain levels of serotonin. One of the most important ways to achieve this goal is by providing the body with amino acid tryptophan, or even better 5-HTP (5-Hydroxy L-Tryptophan), which is made from tryptophan.

Because of its ability to boost serotonin levels, 5HTP synthesized from tryptophan, has been used to help individuals suffering from numerous disorders, including migraines, tension headaches, depression, or anxiety.

Numerous studies have demonstrated that the amino acid 5-HTP (5-Hydroxy L-Tryptophan), which is made from tryptophan, and that in turn is used by the body to produce serotonin is helpful in coping with obesity, insomnia, anxiety, and depression. Researchers found that people using the 5-HTP had significantly greater levels of satiety (they felt more full after consuming their meals) than the control group. The 5-HTP group also had a greater decrease in hip circumference and lower BMI (body mass index) than the control group. 5-HTP is also regarded as a potent antioxidant able to protect the body against the free-radical damage, thus reducing the risk of numerous health problems such as cardiovascular diseases, fatigue, cancer, etc.

It is very important to remember that sufficient amounts of vitamin C, B3, B6 (pyridoxine), folate, zinc, and magnesium are necessary for the formation of tryptophan, which, in turn, is necessary in our body for the synthesis of serotonin. Apart from that, it has been shown that magnesium, vitamin B6 and B3 can also assist the conversion of tryptophan to serotonin.

It is true that tryptophan is also found in animal foods especially milk, but animal sources (including milk and dairy) are much higher in other competitive amino acids thus hindering the absorption of tryptophan. Because tryptophan is an amino acid (protein), therefore a diet rich in other types of protein (meat and dairy products) greatly hinders tryptophan from passing from the blood to your brain. It is so because tryptophan has to compete with many other amino acids (proteins) while trying to enter the brain and as a result, only a small amount of this important amino acid gets in. That is another reason why it is much better to supplement tryptophan in the form of 5HTP instead of relying on animal foods. In addition, unlike 5HTP, meat and dairy products also contain numerous high-risk factors such as cholesterol, triglycerides, antibiotics, or dioxins.

A study by Professor J. Wurtman (2009) demonstrated that tryptophan, which is the building block of serotonin, can get into our brains only when sweet unrefined carbohydrates are consumed. Thus, more serotonin is made after you consume sweet unrefined carbohydrates such as fruits (especially bananas and dried fruits).

Numerous studies have demonstrated that the amino acid 5-HTP (5-Hydroxy L-Tryptophan), which is made from tryptophan, and that in turn is used by the body to produce serotonin is helpful in coping with migraines, obesity, insomnia, anxiety, and depression. 5-HTP is also regarded as a potent antioxidant able to protect the body against the free-radical damage, thus reducing the risk of numerous health problems such as cardiovascular diseases, fatigue, cancer, etc.

In 1989, the U.S. Centers for Disease Control reported evidence linking L-tryptophan supplements to a disorder characterized by an elevated white blood cell count. However, subsequent research showed that it was contaminants in the supplements, not the tryptophan, that was responsible for the problem.

L-TRYPTOPHAN VS 5HTP

Supplementing with L-tryptophan instead of 5-HTP is a much less effective way to increase serotonin levels because L-tryptophan has to be first converted to 5-HTP. It means that taking L-tryptophan will result in producing less serotonin than after supplementing with 5-HTP. Both L-Tryptophan and 5-HTP must cross the blood-brain barrier to make serotonin in the brain. However, unlike L-Tryptophan 5-HTP doesn’t have to compete with other amino acids to cross the blood-brain barrier. As a result, 5-HTP is much more effective in getting into the brain than it is in case of L-tryptophan. For this reason, 5-HTP is regarded as a significantly more effective form of tryptophan in boosting brain serotonin levels. The human body uses L-tryptophan to produce a number of compounds including Niacin (Vitamin B3), but 5-HTP is only used to produce serotonin and melatonin (from serotonin). Your body can convert L-Tryptophan and 5-HTP to serotonin in the liver and also in the brain. When Part of L-tryptophan can be converted to serotonin in the liver and this serotonin can’t be used by the brain to improve mood or prevent migraine.

While supplementing with L-tryptophan and 5-HTP it is also very important to make sure that the first is taken with vitamin B3 and the second with vitamin B6. Tryptophan is crucial in boosting serotonin levels because serotonin is made in the body from tryptophan. Tryptophan is first converted in the liver into 5HTP (5-Hydroxy L-Tryptophan) by the enzyme tryptophan hydroxylase with the help of vitamin B3 (niacin). The problem, however, is that when the liver attempts to convert tryptophan to 5HTP in the absence of adequate levels of vitamin B3, it will use tryptophan to synthesize it, and it uses 60mg of tryptophan to produce 1mg of niacin, thus leading to tryptophan and serotonin deficiency! That is why if L-tryptophan supplements are taken instead of 5-HTP it should be used with B3. On the other hand, when 5-HTP gets into the liver another enzyme (decarboxylase) converts it to 5HT, but it can do it effectively only with the help of vitamin B6 (pyridoxine). Unfortunately, when the body is deficient in this vitamin, the liver will convert 5HTP to some toxic metabolites! For this reason, 5-HTP, which effectiveness in boosting serotonin levels is higher than that of L-tryptophan, should be supplemented with pyridoxine (vitamin B6).

Please keep in mind that, Tryptophan (from food or supplements) requires a lot of Vitamin B3 (or Niacinamide) in the body to be converted to 5HTP and therefore when the liver tries to convert tryptophan to 5htp in the absence of adequate levels of Vitamin B3, it will use tryptophan to manufacture Vitamin B3 and it uses 60mg of tryptophan to produce the only 1mg of Vitamin B3, thus leading to tryptophan and serotonin deficiency!!! That is why if L-tryptophan is used instead of 5HTP it should be taken with at least 100mg of B3.

Unlike 5-HTP, L-tryptophan must be taken on an empty stomach between 3 – 4 pm and again at bedtime with a fruit juice (or a smoothie). It also shouldn’t be taken with meals high in protein as other amino acids hinder the formation of serotonin from L-tryptophan. Also, complex carbohydrates improve conversion into Serotonin.

5-HTP also requires the presence of some vitamins and minerals to be converted to another form (5HT), but much less than it is in the case of L-tryptophan to be converted to 5HTP. 5HTP in our liver is converted to 5HT but it can do it only with the help of Vitamin B6. However, if you are even mildly deficient in Vitamin B6, this tryptophan will be converted to toxic metabolites, by the liver! It is therefore very important 5-HTP should be taken with either vitamin B6 or multivitamin which is high in B6, B complex, or such as Healthy Mega.

5-HTP is well absorbed from an oral dose, with about 70 percent ending up in the bloodstream. It easily crosses the blood-brain barrier and effectively increases the central nervous system (CNS) synthesis of serotonin.

Some people say they don’t need 5-HTP because they can get tryptophan from the food such as turkey or other meats. Well, experts say that eating high protein foods containing tryptophan does not increase serotonin because most foods including turkey contain other powerful amino acids that prevent tryptophan from being absorbed and pass the blood-brain barrier.

According to the scientific paper by Professor T.C. Bridsall, 5-HTP is very well absorbed and effective in boosting serotonin in the brain: “5-Hydroxytryptophan (5-HTP) is the intermediate metabolite of the essential amino acid L-tryptophan (LT) in the biosynthesis of serotonin. Intestinal absorption of 5-HTP does not require the presence of a transport molecule, and is not affected by the presence of other amino acids; therefore it may be taken with meals without reducing its effectiveness. Unlike LT, 5-HTP cannot be shunted into niacin or protein production… 5-HTP is well absorbed from an oral dose, with about 70 percent ending up in the bloodstream. It easily crosses the blood-brain barrier and effectively increases the central nervous system (CNS) synthesis of serotonin. In the CNS, serotonin levels have been implicated in the regulation of sleep, depression, anxiety, aggression, appetite, temperature, sexual behaviour, and pain sensation. Administration of 5-HTP has been shown to be very beneficial in dealing with a wide variety of health problems, including depression, fibromyalgia, binge eating associated with obesity, chronic headaches, and insomnia.” (SOURCE >)

TRYPTOPHAN & ELEVATED WHITE BLOOD CELL COUNT

In 1989, the U.S. Centers for Disease Control reported evidence linking L-tryptophan supplements to a disorder characterized by an elevated white blood cell count. However, subsequent research showed that it was contaminants in the supplements, not the tryptophan, that was responsible for the problem.

VITAMINS & MINERALS REQUIRED TO INCREASE SEROTONIN FROM TRYPTOPHAN

It is very important to remember that sufficient amounts of vitamin C, B3, B6 (pyridoxine), folate, zinc, and magnesium are necessary for the formation of tryptophan, which, in turn, is necessary in your body for the formation of serotonin. Apart from that, it has been shown that magnesium, vitamin B6 and B3 can also assist the conversion of tryptophan to serotonin. For this reason, our diet should be high in those nutrients and for the best results, good quality supplements can be used.

A deficiency of the active form of Vitamin B6, P5P, may cause tryptophan to be used in the production of an organic acid called kynurenine, leading to low serotonin and melatonin, thus contributing to depression and sleep difficulties (>).

5HTP in our liver is converted to 5HT, but it can be done only with the help of Vitamin B6. However, if you are even mildly deficient in this vitamin, the liver will convert tryptophan to toxic metabolites rather than to 5-HT! It is therefore very important to always take 5-HTP with either Vitamin B6, B complex, or multivitamin which contains at least 10mg of B6.

MAKE SURE YOU TAKE NIACIN (VITAMIN B3) SUPPLEMENT

Low intake of Vitamin B3 from dietary sources or supplements may greatly contribute to the development of depression because almost all amino acid tryptophan we get from food has to be converted to Vitamin B3 and nothing is left to make serotonin in the brain thus leading to its deficiency and depression.

Vitamin B-3 is made in the body from the amino acid tryptophan. On the average 1 mg of vitamin B-3 is made from 60 mg of tryptophan, about 1.5% Since it is made in the body it does not meet the definition of a vitamin; these are defined as substances that can not be made. It should have been classified with the amino acids, but long usage of the term vitamin has given it permanent status as a vitamin. The 1.5% conversion rate is a compromise based upon the conversion of tryptophan to N-methyl nicotinamide and its metabolites in human subjects. I suspect that one day in the far distant future none of the tryptophan will be converted into vitamin B-3 and it then will truly be a vitamin. According to Horwitt [1], the amount converted is not inflexible but varies with patients and conditions. For example, women pregnant in their last three months convert tryptophan to niacin metabolites three times as efficiently as in non-pregnant females. Also, there is evidence that contraceptive steroids, estrogens, stimulate tryptophan oxygenase, the enzyme that converts the tryptophan into niacin.

This observation raises some interesting speculations. Women, on average, live longer than men. It has been shown for men that giving them niacin increases their longevity. [2] Is the increased longevity in women the result of the greater conversion of tryptophan into niacin under the stimulus of their increase in estrogen production? Does the same phenomenon explain the decrease in the incidence of coronary disease in women?

The best-known vitamin deficiency disease is pellagra. More accurately it is a tryptophan deficiency disease since tryptophan alone can cure the early stages. Pellagra was endemic in the southern U.S.A. until the beginning of the last world war. It can be described by the four D’s: dermatitis, diarrhoea, dementia and death. Dementia is a late-stage phenomenon. In the early stages, it resembles much more the schizophrenias, and can only with difficulty be distinguished from it. The only certain method used by early pellagrologists was to give their patients in the mental hospitals small amounts of nicotinic acid. If they recovered they diagnosed them pellagra, if they did not they diagnosed them schizophrenia. This was good for some of their patients but was not good for psychiatry since it prevented any continuing interest in working with the vitamin for their patients who did not recover fast, but who might have done so had they given them a lot more for a much longer period of time, the way we started doing this in Saskatchewan. I consider it one of the schizophrenic syndromes.

L-DOPA LEADS TO TRYPTOPHAN DEFICIENCY

L-dopa – a synthetic form of dopamine is the most frequently prescribed medication for Parkinson’s. Although it often produces some short-term symptomatic benefits yet the problem is that it never leads to recovery because it doesn’t address the underlying causes of this condition including mitochondrial dysfunction, nutritional deficiencies, high levels of toxins, or oxidative stress in the brain. In addition, L-dopa causes nausea and deficiency of nutrients that are precursors to major neurotransmitters including serotonin (best antidepressant and feel-good hormone), L-tryptophan (precursor of serotonin), L-tyrosine, Vitamin B6, or sulphur compounds that are required to produce glutathione (>, >, >, >).  These side effects lead to other neurological problems and mood disorders (mostly triggered by reduced serotonin levels). Research gives evidence that L-dopa causes a long-term worsening of Parkinson’s disease (>).

DOSAGE

500mg 1 to 3 times daily before meals or as recommended by a practitioner. Not recommended for children under 12 yrs unless supervised by a healthcare professional.

CONTRAINDICATIONS & SAFETY

Known contraindications: Unknown

Interactions: None known

Safety: No safety issues

RELATED ARTICLES

SEROTONIN LOW >

DEPRESSION & ANXIETY >

SOURCES

Groff J.L et al. Advanced Nutrition and Human Metabolism. 1995 Robert Garrison. Lysine, Tryptophan, and other amino acids. Food for our brains, maintenance for our bodies. 1982 Kate Udall. Amino acids – the building blocks of life.1997 Murray and Pizzorno. Textbook of Natural Medicine. 1999 Protein and amino acid requirements in human nutrition. WHO Technical Report Series. 935. 2002

Lam, D. D., Garfield, A. S., Marston, O. J., Shaw, J., and Heisler, L. K. Brain serotonin system in the coordination of food intake and body weight. Pharmacology, Biochemistry and Behavior. 2010;97(1):8491

Meltzer CC, Smith G, Price JC, et al. 1998. Reduced binding of [18F] altanserin to serotonin type 2A receptors in aging: persistence of effect after partial volume correction. Brain Res 1998; 813: 167-171.

Li D, He L. Meta-analysis supports association between serotonin transporter (5-HTT) and suicidal behavior. Mol Psychiatry 2006; 12:47-54.

N Uceyler, M Schütt, F Palm, et al (2010) Lack of the serotonin transporter in mice reduces locomotor activity and leads to gender-dependent late onset obesity. International Journal of Obesity (2010) 34, 701711.

Michael T. Murray (1998). 5-HTP: The Natural Way to Boost Serotonin and Overcome Depression, Obesity, and Insomnia. June 1st 1998 Bantam.

Hirsch M, et al. Unipolar depression in adults and selective serotonin reuptake inhibitors (SSRIs): Pharmacology, administration and side effects. www.uptodate.com/home. Accessed June 5, 2013.

Sargent, B. J., and Moore, N. A. New central targets for the treatment of obesity. Br J Clin Pharmacol. 2009; 68 (6): 85260.

“Leptin-Serotonin Pathway Offers New Clues For Obesity And Osteoporosis Prevention.” Medical News Today. (2009, September 5).

Joseph E. Pizzorno Jr & Michael T. Murray. The Textbook of Natural Medicine. Second Edition. Volume 1. 1999.

Effect of chronically administered L-Dopa on Dopa/5HTP decarboxylase and tyrosine and tryptophan hydroxylases in cat brain Link Here

Int J Neurosci. 1992 Nov-Dec; 67(1-4):127-44.

Breum L, Rasmussen MH, Hilsted J, Fernstrom JD. Twenty-four-hour plasma tryptophan concentrations and ratios are below normal in obese subjects and are not normalized by substantial weight reduction. The American journal of clinical nutrition. May 2003; 77(5):1112-1118.

Cangiano C, et al. Effects of oral 5-hydroxy-tryptophan on energy intake and macronutrient selection in non-insulin dependent diabetic patients. Int J Obes Relat Metab Disord. 1998; 22:648-654.

Cangiano C, Ceci F, Cascino A, et al. Eating behavior and adherence to dietary prescriptions in obese adult subjects treated with 5-hydroxytryptophan. J Clin Nutr. 1992; 56: 863-867.

Young SN (2007). “How to increase serotonin in the human brain without drugs”. J Psychiatry Neurosci 32 (6): 3949. PMC 2077351. PMID 18043762.

Hales, S.E.; Hales, C.N. (2004). “Lifespan: catch-up growth and obesity in male mice”. Nature. 427 (6973): 4112. Bibcode: 2004Natur. 427. 411O.

Martinez A, Knappskog PM, Haavik J. A structural approach into human tryptophan hydroxylase and its implications for the regulation of serotonin biosynthesis. Curr Med Chem 2001 Jul; 8(9): 1077-91. 2001. PMID: 15980.

Moore P, Landolt HP, Seifritz E, et al. Clinical and physiological consequences of rapid tryptophan depletion. Neuropsychopharmacology 2000 Dec; 23(6): 601-22. 2000. PMID: 16020.

Joseph Mercola, Light Therapy Promising for Treating Major Depression, January 26, 2011:

http://articles.mercola.com/sites/articles/archive/2011/01/26/light-therapy-promising-for-treating-major-depression.aspx |

University Of Pennsylvania School Of Medicine (2005, July 11). Mood Lighting: Penn Researchers Determine Role Of Serotonin In Modulating.

Taking Antidepressants: Your Comprehensive Guide to Starting, Staying On, and Safely Quitting, by Michael D. Banov, M.D. (Sunrise River Press, 2010).

The Antidepressant Solution: A Step-by-Step Guide to Safely Overcoming Antidepressant Withdrawal, Dependence, and “Addiction,” by Joseph Glenmullen, M.D. (Free Press, 2006).

Curr Opin Neurobiol. 2013 Feb 2. pii: S0959-4388 (13) 00027-5.

Prog Neurobiol. 2000 Jan; 60(1):13-35.

J Nutr. 2012 Dec; 142(12):2236S-2244S.

J Exp Biol. 2002 Dec; 205(Pt 23):3679-87.