The association between tryptophan levels and postpartum mood disorders: a systematic review and meta-analysis.

Over 50% of women experience mood disturbance in the postpartum period, with significant implications for maternal and infant health but identifying those at risk is not easily possible. The essential amino acid, tryptophan (TRP) through its neuroactive metabolites, has been implicated in the pathology of mood disorders. Thus, TRP levels tested in the peripartum period have been proposed as a potential biomarker for subsequent development of postpartum mood disturbances, in particular postpartum depression (PPD). A systematic review and meta-analysis following PROSPERO guidelines [CRD42021252462] was conducted on peer-reviewed, English language studies that measured blood levels of TRP during the postpartum period in women who were also evaluated for postpartum "blues" or PPD. Thirteen studies met the inclusion criteria, of which five studies contained sufficient data to conduct a meta-analysis. Low total TRP levels in postpartum days 1 to 5 were significantly associated with PPD (SMD: -5.39, 95%CI [-7.72, -3.05]). No significant association was found between free TRP levels in the postpartum period and PPD (SMD: -3.43, 95%CI [-7.76, 0.89]). Our findings confirm the necessity for more replicable designed studies regarding TRP and its relationship to postpartum depression. If there were greater clarity regarding TRP metabolism during pregnancy, then the next step would be to consider measuring total plasma TRP levels on postpartum days 1 to 5 to identify women at greater risk of developing PPD.