This double-blind, randomized, placebo-controlled parallel trial evaluates the effects of maternal 5-methyltetrahydrofolate (5-MTHF) supplementation during breastfeeding. Thirty-six lactating mother-infant dyads will be randomized (1:1) to receive 5-MTHF or placebo for 6 weeks, stratified by infant sex and mode of delivery. Tolerability and adverse events will be monitored.
Pre- and post-intervention assessments include breast milk one-carbon metabolites and oligosaccharides; maternal plasma one-carbon metabolites and metabolic health markers. Maternal mental health will be evaluated using the SCL-90-R questionnaire. A follow-up visit at 4 months will reassess infant anthropometry and microbiome outcomes.