Can Tryptophan Make You Smarter?

Q I have read that tryptophan supplementation can make you smarter. Is there any truth to that?

SAMUEL Denver

A It is now known that the creation of new neurons—a process called neurogenesis—is possible. Not only is this true in lower species, but in humans too. In fact, it is now known to be a lifelong process, beneficially altering two particular areas of the brain. On the other hand, a decrease in the production of new neurons is related to cognitive decline and aging. In the brains of marmoset monkeys, a recent study has found that newly generated cells (in the dentate gyrus of the hippocampus) were significantly lower in aged monkeys.1 In fact, the older they became, the fewer new cells were generated. According to the researchers, this “suggest[s] the possibility that similar alterations occur in the human brain.”

The researchers reasoned that this age-related decline of neurogenesis may be caused by the decrease with age of the neurotransmitter serotonin, which has been known to promote hippocampal neurogenesis through actions at a certain serotonin receptor. The knowledge that both serotonin and the serotonin receptor decrease with age, “raise[s] the possibility of a negative effect on neurogenesis.”

Another report found that serotonin-induced increases in adult cell proliferation and neurogenesis are mediated through different and common 5-HT receptor subtypes in the dentate gyrus and the subventricular zone.2 The researchers had previously reported that the reduction of newborn cells in these regions followed significant serotonin depletion.

More recently, it was reported that enhanced serotonergic neurotransmission in the hippocampus following tryptophan administration improves learning acquisition and memory consolidation in rats.3 The rats were given tryptophan orally daily for 6 weeks in amounts of 50 or 100 mg/kg of body weight. The finding showed that long-term memory as measured by a water maze test was significantly improved. The enhancement was 66.5% at the 50 mg/kg dose and 72.4% at the 100 mg/kg dose. Short-term memory was also measured and found to be improved significantly by 54% at the 100 mg/kg dose. However, there was no benefit at the 50 mg/kg dose.

Finally, the length of time it took the rats to relocate a submerged platform in the water maze was measured. These results, representing memory consolidation, measured retention latency at 1 hour and 24 hours after training. There was a significant decrease in retention latency at both doses of tryptophan after 24 hours. This meant that rats remembered the location of the platform longer.

So, in answer to your question, it is quite possible that taking a tryptophan supplement can enhance memory. Doesn’t that make you smarter? (Thanks to Durk & Sandy for this insight. Please see their Life Extension News write up in the March 2008 issue of this publication.)

  1. Leuner B, Kozorovitskiy Y, Gross CG, Gould E. Diminished adult neurogenesis in the marmoset brain precedes old age. Proc Natl Acad Sci U S A 2007 Oct 23;104(43):17169-73.
  2. Banasr M, Hery M, Printemps R, Daszuta A. Serotonin-induced increases in adult cell proliferation and neurogenesis are mediated through different and common 5-HT receptor subtypes in the dentate gyrus and the subventricular zone. Neuropsychopharmacology 2004 Mar;29(3):450-60.
  3. Haider S, Khaliq S, Haleem DJ. Enhanced serotonergic neurotransmission in the hippocampus following tryptophan administration improves learning acquisition and memory consolidation in rats. Pharmacol Rep 2007 Jan-Feb;59(1):53-7.



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