No effect of oral tyrosine on total tyrosine levels in breast milk: implications for dietary supplementation in early postpartum

Postpartum depression (PPD) is the most common complication of childbearing with a 13 % prevalence rate, and there is no widespread approach for prevention. There is an appealing theoretical rationale for oral tyrosine to help prevent PPD. However, the effect of oral tyrosine on its total and free concentrations in breast milk and plasma of breastfeeding mothers is not known. Twenty-four healthy breastfeeding women were randomly assigned to 0, 2, 5, or 10 g of oral tyrosine. Free and total tyrosine in breast milk and free tyrosine in plasma were measured. Free tyrosine was also measured in 12 different infant formulas. Total tyrosine in breast milk did not rise, but there was a slight tendency towards a reduction (up to -12 %; repeated measures ANOVA (RMANOVA): p = 0.074). Maternal plasma tyrosine rose (RMANOVA: p < 0.005). In breast milk, 98 % of tyrosine was in proteins or peptides and 2 % was free. Free tyrosine levels in breast milk rose in each group (RMANOVA: p < 0.005), but levels were within the range found in common infant formulas. The negligible effect of oral tyrosine on its concentration in breast milk supports further development of oral tyrosine as part of a prevention strategy for PPD.