Associations between breast-milk folate vitamers and various folate-related SNPs. (A) Association between the MTHFR 677C>T SNP and breast-milk UMFA (P = 0.004). (B and C) Association between the MTHFR 1793G>A SNP and breast milk reduced folates (P = 0.04) and 5-methyl-THF (P = 0.04). (D) Association between the MTRR 66A>G SNP and breast milk reduced folates (P = 0.02). Reduced folates represent the sum of THF, 5-methyl-THF, 5,10-methenyl-THF, and 5-formyl-THF. Associations were assessed using the Wald's test using PLINK. Associations were considered significant if P ≤ 0.01 based on Bonferroni correction for multiple testing. The LOD for UMFA was <0.9 nmol/L; values that fell below the LOD were assigned a value of one-half the LOD for analysis. LOD, limit of detection; SNP, single nucleotide polymorphism; THF, tetrahydrofolate; UMFA, unmetabolized folic acid.