Background: Vitamin D deficiency in pregnancy and lactation increases the risk of adverse perinatal outcomes; however,
although Vitamin D supplementation during pregnancy and lactation is recommended, suggested dose ranges vary.
Objective: To determine whether vitamin D31,800 IU/d supplementation in lactating mothers improves their vitamin D status and breast-feeding milk.
Material and Method: This was a randomized, placebo–controlled study of Thai pregnant women in their third trimester. A total of 76 Thai lactating mothers and their breast-fed infants were studied with maternal 25 Hydroxyvitamin D 25 (OH) D levels of 10-30 ng/ml determined using Liquid Chromatography Mass Spectrometry Tandem (LC-MS/MS). One group received vitamin D3 1,800 IU/d supplementation for 6 weeks, and members of the other group were given a placebo. 25 (OH) D level of colostum and 6-week serum from breast-fed milk were measured by High Performance Liquid Chromatography (HPLC). The data from the two groups were analyzed and compared.
Results: The mean (+SD) maternal age was 27.16+5.13 years, and mean body mass index (BMI) was 22.29+5.08 kg/m2. At
6 weeks, maternal 25 (OH) D levels had increased significantly in the vitamin D group (VD) 68.30+15.40 nmol/L compared
to 55.15+13.57 nmol/L in the placebo group (p<0.001) measured using the Liquid Chromatography-Mass Spectrometry
Tandem (LC-MS/MS) method. Breast-fed milk did not show any significant incremental change in 25 (OH) D levels measured by High Performance Liquid Chromatography (HPLC); however, the change in 25 (OH) D levels in breast milk in the VD group was significantly different from that of the placebo group (p = 0.005).
Conclusion: Vitamin D3 supplementation during lactation can increase 25 (OH) D levels in Thai breast-fed mothers. Further work is needed to determine the duration of vitamin D supplementation to normalize breast milk and breast-fed
infants’ 25 (OH) D level at over 75 nmol/L.

Keywords: Breast-fed milk, Vitamin D supplementation, Lactation