Life Extension Magazine April 2008
Why Aging People Become Depressed, Fatigued, and Overweight
By William Faloon
A daily dose of 6,000 mg of L-tryptophan significantly decreased mood swings, tension, and irritability in women with premenstrual syndrome.49 The meta-bolism of tryptophan is impacted by the different phases of a woman’s cycle,50 and therefore hormonal changes during the menstrual cycle may negatively affect the availability of tryptophan for conversion into serotonin.
Carbohydrate Cravings and Weight Loss
Some obese people consume carbohydrate-rich foods frequently and preferentially, because they have a persistently low plasma tryptophan ratio, as well as low tryptophan uptake into the brain.51 Remember that serotonin levels are enhanced by carbohydrate ingestion as insulin release accelerates the serum removal of other amino acids that compete for transport through the blood-brain barrier.
Increasing the L-tryptophan levels in blood plasma is also known to have an appetite-suppressing effect that mainly impacts carbohydrate consumption.52,53 Presumably the supplemental tryptophan would enhance the release of serotonin from brain neurons to diminish appetite for carbohydrates, which helps with loss of body weight. In addition, obese subjects are often insulin-resistant, and diminished insulin action may cause low plasma tryptophan ratios33 because of the peripheral effects of insulin on the uptake and utilization of other amino acids.
A study was done to measure L-tryptophan in the blood plasma of obese patients to assess the plasma tryptophan ratio to large neutral amino acids (tyrosine + phenylalanine + leucine + isoleucine + valine). The results showed the plasma tryptophan ratio was well below the normal ratio for humans.51 If elevation of the tryptophan in relation to large neutral amino acids occurs, more tryptophan is allowed into the brain to induce serotonin synthesis and influence functions of serotonin (mood, appetite, sleep, and hunger). This study helps show why obese people often have uncontrollable appetites, i.e., they have too little tryptophan in relation to other large neutral amino acids in their blood.
When these obese patients were given 1,000 mg, 2,000 mg, or 3,000 mg doses of L-tryptophan one hour before meals to raise the amount of tryptophan relative to the large neutral amino acids, a significant decrease in caloric consumption was observed. The majority of the reduction in caloric intake was due to the amount of carbohydrates, not protein, consumed. The only side effects observed were a mild decrease in mental alertness, mild dizziness, and mild drowsiness.54
In a double-blind, placebo-controlled study, obese patients on protein-rich diets who received tryptophan (750 mg twice daily orally) had significant weight loss, compared with a placebo group. A moderate dose of tryptophan supplementation did not cause any side effects such as mid-day sleepiness or fatigue.55 The effects of reducing tryptophan levels were also studied in a 7-year-old girl with severe anorexia. When tryptophan levels were reduced, spontaneous eating occurred for the first time in 4.5 years. The spontaneous eating ceased when the tryptophan intake was increased.56
How Aging Reduces Tryptophan-Serotonin Levels
As a result of normal aging, inflammatory cytokine levels increase. A little-known adverse effect is that inflammatory cytokines (such as tumor necrosis factor alpha and interferon alpha) cause induction of the tryptophan-degrading enzyme IDO (indoleamine 2,3-dioxygenase).
You might think that aging people could compensate for the tryptophan-degrading effects of IDO by consuming higher doses of tryptophan supplements. The problem is that in the presence of high blood levels of tryptophan, the other tryptophan-degrading enzyme TDO is also elevated.
So consuming large amounts of L-tryptophan (oral doses of 4,000 mg and greater) will not generate more serotonin because TDO will be induced. Yet if aging people fail to get more tryptophan into their bodies, brain serotonin levels will plummet because the higher IDO enzyme activity will degrade what little tryptophan remains in the blood.
Engineering Around This Problem
Fortunately, the new understanding of how tryptophan is degraded in aging humans provides a basis for engineering a natural solution around this epidemic problem.
First of all, we know from studies in patients with high levels of systemic inflammation that if sufficient niacinamide is given, the degradation of tryptophan in the body is significantly reduced.57,58 We also know that the amino acid lysine competes with tryptophan in the same oxidative degradation pathway. This means that in the presence of lysine, less tryptophan is oxidized.59
Tryptophan, however, can still be degraded by the IDO enzyme that increases as humans age. Nutrients such as curcumin inhibit interferon-induced nuclear factor-kappa-B and COX-2 expression and may limit the induction of IDO, thus making more tryptophan available for conversion to serotonin in the brain.60
It is thus possible for aging people to supplement with a modest dose of tryptophan (1,000-1,500 mg per day) and significantly decrease tryptophan oxidation/degradation, as long as lysine, niacinamide, and the proper cytokine-suppressing nutrients are taken with it to neutralize the effects of the IDO enzyme.
Cofactors that facilitate the conversion of tryptophan to serotonin in the brain are vitamin B6, magnesium, and vitamin C.60-62 These nutrients are already taken by most health-conscious people.
An important factor in the decision to supplement with L-tryptophan is its excellent tolerability and the lack of development of tolerance during long-term use. Furthermore, L-tryptophan does not cause difficulties when trying to wake up the next morning.63
The minimal dose of L-tryptophan for effective treatment of insomnia may be at least 1,000 mg, and repeat administration of L-tryptophan may be required for improvement in chronic, well-established, sleep-onset insomnia or insomnia characterized by both sleep-onset and sleep-maintenance abnormalities.63 Low doses of L-tryptophan (250 to 500 mg) may not offer a significant benefit on sleep latency.64 For those with insomnia who wish to try L-tryptophan, a strong initial dose (1,000 to 4,000 mg) is recommended for the first week, followed by a lower maintenance dose (500 mg to 1,000 mg).
Evening oral doses of tryptophan as low as 250 mg have been shown to improve sleep quality, although the typical dosage range for sleep disorders and depression is 1,000-3,000 mg daily. Safe and effective dosages for other disorders range from 500 mg to 4,000 mg/day, while doses around 3,500 mg/day have been used short term as a smoking cessation intervention.65
Tryptophan is oxidized in the liver by tryptophan-2,3-dioxygenase (TDO), an enzyme that is induced both by glucocorticoids and by large doses of tryptophan itself. The enzyme activity of TDO increases after tryptophan administration66 and results in a relatively short half-life of tryptophan remaining in the plasma.67 Thus, tryptophan is often given in divided daily doses instead of a single dose. A single dose of 3,000 mg is sufficient to keep human brain serotonin synthesis maximized for about eight to twelve hours.68 Giving three daily doses of 2,000 mg will probably keep the rate-limiting tryptophan hydroxylase enzyme in the brain fully saturated for most of each 24-hour period, meaning that brain serotonin levels would be maintained at a constant optimal level.
Tryptophan Blackout Is Lifted!
American consumers can once again obtain tryptophan as a dietary supplement. Particularly compelling news is the discovery that aging people produce tryptophan-degrading enzymes, which can be neutralized by the simultaneous ingestion of nutrients that block pro-inflammatory cytokines and mitigate tryptophan depletion via other oxidative pathways.
A novel formula is now available that combines pharmaceutical-pure tryptophan with a blend of nutrients designed to nourish the brain with optimal levels of serotonin.
Based on hundreds of scientific studies, depletion of serotonin may contribute to age-related weight gain, depression, insomnia, anxiety, and loss of feeling of well-being.
By restoring serotonin to optimal levels, aging people can regain the neurotransmitter balance enjoyed in their youth. Those suffering from age-related weight gain or sleep difficulties could experience significant improvement by using tryptophan to increase their brain serotonin to youthful levels.
If you have any questions on the scientific content of this article, please call a Life Extension Health Advisor at 1-800-226-2370.
To learn who should not take high-dose tryptophan supplements, refer to the Tryptophan Precautions section on the following page.
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