L-Tryptophan, as a precursor to serotonin, is invested in the cognitive process. Serotonin plays a large role in cognition, including staving off Alzheimer's disease and depression. In particular, it seems to have a positive effect on women who have participated in studies. As yet, doctors have not worked out tryptophan's role in the complex cognitive relationship that involves more than just serotonin.

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