Increased blood serotonin concentrations are correlated with reduced tension/anxiety in healthy postpartum lactating women.

The serotonin (5-HT) system in the brain plays an important role in mood regulation. The postpartum period is considered a high-risk time for mood and anxiety disorders. We assessed changes in 5-HT levels in whole blood (as an indicator of brain 5-HT concentrations) and mood states before and after delivery in 28 healthy, lactating postpartum women. Mood states were evaluated using Profile of Mood States questionnaires (POMS). Measurements were done on the same day in early (first week) and late (third-fourth and sixth-seventh weeks) postpartum, and compared with those in the third trimester and in age-matched, healthy, non-pregnant women. Mean 5-HT concentrations were significantly higher and mean tension/anxiety scores of POMS were significantly lower in late (but not early) postpartum than in the third trimester or non-pregnant controls. 5-HT concentrations correlated with tension/anxiety in the third trimester and late postpartum, indicating an important role for the 5-HT system in the regulation of tension/anxiety in healthy postpartum women. The mechanism underlying the changes in the 5-HT system may be rapid inhibition induced by the marked decrease in estradiol after delivery and gradual excitation caused by lactation-induced brain oxytocin release during the postpartum period.