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A systematic review of the effect of L-tryptophan supplementation on mood and emotional functioning.

  • 2020-04-10
  • Journal of dietary supplements 18(3)
    • Asako M Kikuchi
    • Aya Tanabe
    • Yoshihiro Iwahori

Study Design

Type
Systematic Review
Population
healthy adults
Methods
systematic review of RCTs, searching PubMed, the Cochrane Library, and Ichu-shi according to PRISMA guidelines
L-tryptophan (TRP), one of the essential amino acids in humans, is a precursor of serotonin, and hence its intake is closely related to the suppression of depressed and anxious moods. We did a systematic review of RCTs to examine the effects of tryptophan intake on the mood of healthy adults by searching PubMed, the Cochrane Library, and Ichu-shi according to PRISMA guidelines. As a result, 11 RCTs met the criteria and were accepted. Four RCTs showed the effects of tryptophan intake on negative feelings and happy feelings in healthy individuals, with significant differences between the treatment and the control groups. This suggests that TRP intake may be an effective approach to decrease anxiety and increase positive mood in healthy individuals. On the other hand, the effectiveness of TRP for aggressive feelings was not recognized. Reviewing these 11 RCTs, we concluded that taking 0.14-3 g of TRP per day in addition to the usual meal can be expected to improve the mood of healthy individuals. In order to estimate the optimum amount of TRP intake more accurately, further studies need to be conducted with more appropriate settings of intake period, intake frequency, and intake method.

Research Insights

  • L-Tryptophan→Improved Mood

    Four RCTs showed the effects of tryptophan intake on negative feelings and happy feelings in healthy individuals, with significant differences between the treatment and the control groups. This suggests that TRP intake may be an effective approach to decrease anxiety and increase positive mood in healthy individuals.

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    0.14-3 g/day
  • L-Tryptophan→Reduced Aggressive Feeling

    the effectiveness of TRP for aggressive feelings was not recognized.

    Effect
    Neutral
    Effect size
    Small
    Dose
    0.14-3 g/day
  • L-Tryptophan→Reduced Anxiety

    This suggests that TRP intake may be an effective approach to decrease anxiety and increase positive mood in healthy individuals.

    Effect
    Beneficial
    Effect size
    Moderate
    Dose
    0.14-3 g/day
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