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Does L-tryptophan Affect Women More Than Men?

An interesting study from Europe has found that depletion of the amino acid L-tryptophan affects emotional processing, specifically how we recognize fear. But are women affected more than men?

L-tryptophan is an essential amino acid, which means we must obtain it from our diet, or in supplements. L-tryptophan is found in many animal and plant proteins. It has numerous functions, and has been the subject of several clinical studies for its role as producing the crucial neurotransmitter serotonin.

Serotonin is primarily found in the central nervous system, where it performs important functions. Serotonin affects memory, learning, and emotional response. Serotonin levels are directly related to L-tryptophan intake. This means lack of L-tryptophan results in low serotonin levels, which could lead to sleeplessness. Low levels of serotonin also affect mood.

L-tryptophan depletion: fear recognition different in men and women

Researchers (C Harmer, R Rogers, et al) from the University Department of Psychiatry, Warneford Hospital, Oxford, UK, selected healthy male and female volunteers to examine their responses to emotional expression, particularly fear, if their serotonin levels were low.

In this double-blind trial, the volunteers were randomly given either an amino acid drink specifically lacking in L-tryptophan, or a control drink containing a balanced mixture of amino acids. The acute L-tryptophan depletion reduced their serotonin functions. The volunteers were given a facial expression recognition test five hours after the drink was administered. Six basic emotions were used: fear, anger, disgust, surprise, sadness, and happiness.

Results were interesting, with a distinct difference between male and female response for fear recognition only. L-tryptophan depletion significantly impaired the women’s ability to recognize fear as a facial expression. The male volunteers were not affected, and recognized fear even if their serotonin levels were low. Recognition of all the other basic emotions was comparable in the two groups. The researchers concluded that acute L-tryptophan depletion does affect emotional response, and that this effect is greater in women, compared to men.

Sources: http://www.ncbi.nlm.nih.gov/pubmed/12677354