The effects of dietary tryptophan metabolism on the “vigor” and “confusion” factor of mood

Previously, we reported that tryptophan metabolites affect mood. According to research conducted using the Profile of Mood States (POMS) test, kynurenin and serotonin, which are intermediary metabolites of tryptophan, appear to be correlated with some factors of mood. The present study examined one of the tryptophan metabolites that affects mood using a nutritional method. According to the results of the POMS-test and the nutrition survey, the “vigor” and “confusion” factors of mood were correlated with the intake of tryptophan and niacin. In contrast, serum tryptophan and kynurenin were correlated resting conditions (r = 0.872). Furthermore, correlations were observed between “vigor” and serum kynurenin (r = 0.597) and between “confusion” and serum kynurenin (r = 0.681).

These findings indicate a positive relationship between the intake of tryptophan and niacin and emotional state. Therefore, we investigated the relationship between intake values of tryptophan, niacin and each mood. The observed intake of tryptophan was 610 ± 134 mg/day, while the intake of niacin was 13 ± 4 mg/day. Correlations were observed between intake of tryptophan and “confusion”(r = − 0.602) and “vigor”(r = 0.727), and between the intake of niacin and “confusion” (r = − 0.786) and “vigor”(r = 0.585).

These results suggest that dietary intake of tryptophan and niacin is correlated to tryptophan metabolites and mood. In particular, we suggest that the correlation between serum tryptophan, kynurenin and observed resting conditions of “vigor” and “confusion” resulted from dietary intake of tryptophan.