Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-tryptophan is an essential amino acid that serves as a precursor to serotonin, a neurotransmitter implicated in mood regulation. The rationale for using L-tryptophan in Seasonal Affective Disorder (SAD) is based on the hypothesis that decreased sunlight exposure during fall and winter leads to lower serotonin activity, contributing to depressive symptoms. Supplementing with L-tryptophan may, in theory, increase serotonin synthesis and alleviate mood disturbances.

Some clinical studies have investigated the use of L-tryptophan in depression, with a few small trials specifically examining its effects in SAD. For example, a double-blind, placebo-controlled study published in 1997 (Lam et al., J Affect Disord) found some improvement in depressive symptoms among SAD patients taking L-tryptophan compared to placebo. However, these studies tend to be small, with inconsistent results and methodological limitations. Large-scale, high-quality randomized controlled trials are lacking, and L-tryptophan is not considered a first-line treatment for SAD in clinical guidelines.

Overall, while there is a plausible biological mechanism and limited clinical evidence suggesting potential benefit, the scientific support for using L-tryptophan in SAD is modest. It is sometimes used as an adjunct or alternative therapy, but light therapy and antidepressants remain the main evidence-based treatments for SAD. The evidence rating of 2 reflects suggestive, but not conclusive, scientific findings.

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Nature's Sunshine Free Amino Acids