Sulfated vitamin D metabolites represent prominent roles in serum and in breastmilk of lactating women

Background: Concentrations of vitamin D (VitD) and 25-hydroxyvitamin D (25OHD) in breastmilk are low despite the essential role of VitD for normal infant bone development, yet additional metabolic forms of vitamin D may be present. This study evaluates the contribution of sulfated vitamin D metabolites, vitamin D₃-sulfate (VitD₃-S) and 25-hydroxyvitamin D₃-sulfate (25OHD₃-S) for lactating women and assesses the response to high-dose VitD₃ supplementation.

Methods: Serum and breastmilk were measured before and after 28 days with 5000 IU/day VitD₃ intake in 20 lactating women. Concentrations of VitD₃-S and 25OHD₃-S in milk, and 25OHD₂, 25OHD₃, 25OHD₃-S, VitD₃ and VitD₃-S in serum were determined by mass spectrometry.

Results: Baseline vitamin D status was categorized as sufficient (mean ± SD serum 25OHD₃ 69 ± 19 nmol/L), and both serum VitD₃ and 25OHD₃ increased following supplementation (p < 0.001). 25OHD₃-S was 91 ± 19 nmol/L in serum and 0.47 ± 0.09 nmol/L in breastmilk. VitD₃-S concentrations were 2.92 ± 0.70 nmol/L in serum and 6.4 ± 3.9 nmol/L in breastmilk. Neither sulfated metabolite significantly changed with supplementation in either serum or breastmilk.

Conclusions: Sulfated vitamin D metabolites have prominent roles for women during lactation with 25OHD₃-S highly abundant in serum and VitD₃-S distinctly abundant in breastmilk. These data support the notion that 25OHD₃-S and VitD₃-S may have physiological relevance during lactation and nutritional usage for nursing infants.