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L-Tryptophan gives women a rosy view of the world

Give women a pill three times a day containing one gram of the amino acid L-tryptophan, and within a fortnight their world will look brighter. Psychologists from the University of Oxford reached this conclusion after doing tests on twenty women. The supplement had a subtle but demonstrable effect.


L-tryptophan [structural formula at right] is a precursor of the neurotransmitter serotonin [structural formula shown below]. If your serotonin levels rise, you feel happier. The British researchers showed the effect of high doses of L-tryptophan by carrying out psychological tests designed to measure how people's mood colours their perception.

Half of the women were given a placebo, and the other half took a dose of L-tryptophan that had a maximum effect on their serotonin level. After two weeks the researchers got the women to watch film clips of faces expressing different emotions, like anger, disgust and happiness. The researchers recorded how well the women recognised the emotions. Generally speaking tryptophan improved recognition. Interestingly, L-tryptophan strengthened the recognition of happiness, but reduced the recognition of disgust.

L-Tryptophan gives women a rosy view of the world

A similar distortion occurred when the researchers observed how much attention the women paid to positive and negative words while reading. 'Alimony' turns out to be a positive word for most women. 'Body hair' they react to negatively. The figure below shows that the L-tryptophan supplement heightened the attention the women paid to positive words, but decreased the attention they paid to negative words.

L-Tryptophan gives women a rosy view of the world

The researchers performed the same experiment on eighteen men, but the L-tryptophan had no effect on them.

The researchers think that L-tryptophan may be effective in treating mild depression. One of the characteristics of depression is that you process information in such a way that you become you more sombre. L-Tryptophan has exactly the opposite effect, so it could help to break the vicious circle.

"L-Tryptophan supplementation induces a positive bias in emotional processing in females that is reminiscent of the actions of serotonergic antidepressants", the researchers write. "This highlights a key role for serotonin in emotional processing and lends support to the use of L-tryptophan as a nutritional supplement in people with mild depression or for prevention in those at risk."

Psychopharmacology (Berl). 2006 Jul;187(1):121-30.