Vitamin D concentration in serum and milk of breastfeeding women

Background The hormonally active form of vitamin D generates a number of extraskeletal biological responses, which significantly influences body's homeostasis. The evaluation of vitamin D concentration and supplementing deficiency for breastfeeding women are crucial to maintain good health. The purpose of the study was to measure vitamin D concentration in serum and milk of breastfeeding women, including the influence of supplementation. Hypothesis: Most of breastfeeding women are deficient in vitamin D. Material and methods Blood and breast milk samples were collected consecutively from 46 healthy, non-obese, Caucasian, breastfeeding women at different stages of lactation. The LC-MS/MS method was applied for the measurements of vitamin D. Serum and breast milk vitamin D concentrations in the form of 25(OH)D₂, 25(OH)D₃ and total 25(OH)D were measured in Polish breastfeeding women. Results Serum total 25(OH)D concentrations ranged from 50.2 to 115.7 nmol/L (mean value 75.8±15.5 nmol/L), while breast milk 25(OH)D₃ concentrations ranged between 0.03-1.78 nmol/L (0.64±0.42 nmol/L). More than a half of the examined women (52%) supplement vitamin D using different medications and half of the women showed insufficient (50-75 nmol/L) serum levels of total 25(OH)D. There were no correlations between maternal serum total 25(OH)D concentration and 25(OH)D₃ in breast milk concentration (R=0.27 p=0.07). Breast milk 25(OH)D₃ concentrations were correlated to the duration of breastfeeding (R=0.54 p=0.0002). The median milk 25(OH)D₃ concentration in mothers breastfeeding for more than 9 months was significantly higher (p<0.0005) when compared to women who were breastfeeding for less than 9 months (0.78 vs 0.33 nmol/L). Conclusions Exactly half of the examined women in the reproductive period have deficiency of vitamin D. It seems that vitamin D supplementation is an important element in maintaining the optimal concentration of this vitamin in the body. Prolonged breastfeeding (more than 9 months) affects the concentrations of 25(OH)D₃ in human milk.