Meta-analyses of r and omized controlled trials ( RCTs ) document that physiological vitamin D supplementation during pregnancy is safe and improves vitamin D and calcium status , thereby protecting skeletal health .
Although certain RCTs and /or meta-analyses reported some other beneficial effects , it is still not clear whether vitamin D supplementation  improves fertility or decreases the risk of adverse pregnancy outcomes such as low birth weight , pre-eclampsia and neonatal mortality , or reduces wheeze/asthma in the infants .
Vitamin D deficiency is common and there exists a huge gap between recommended dietary vitamin D intakes and the poor vitamin D supply in the general population .
While vitamin D is important for musculoskeletal health , there are accumulating data suggesting that vitamin D may also be important for fertility , pregnancy outcomes and lactation .
Significant changes in vitamin D metabolism during pregnancy such as increased production of the " active vitamin D hormone " calcitriol support the important role of vitamin D in this setting .
Observational studies show that vitamin D deficiency is a risk marker for reduced fertility and various adverse pregnancy outcomes and is associated with a low vitamin D content of breast milk .
Nevertheless , vitamin D supplementation in pregnant women is frequently required to achieve a sufficient vitamin D status as recommended by nutritional vitamin D guidelines .
Vitamin D activity of breast milk in women randomly assigned to vitamin D3 supplementation during pregnancy.
BACKGROUND Human milk is typically low in vitamin D activity ( VDA ) . Whether the vitamin D content of breast milk at birth can be increased by supplementing the mother during pregnancy has not been reported to the best of our knowledge . OBJECTIVE We examined the effect of vitamin D supplementation during pregnancy on breast-milk VDA in the first 2 mo of lactation . DESIGN Breast-milk sample s were obtained from women who were enrolled in a r and omized , double-blinded , placebo-controlled trial of vitamin D supplementation during pregnancy . Pregnant women were enrolled at 27 wk of gestation and r and omly assigned to the following 3 groups : a placebo group , a group who received one dosage of daily oral vitamin D3 ( 1000 IU ) , or a group who received 2 dosages of daily oral vitamin D3 ( 2000 IU ) . Serum 25-hydroxyvitamin D [ 25(OH)D ] was measured at enrollment , at 36 wk of gestation , and in cord blood at birth . Study participants who were breastfeeding were invited to provide breast-milk sample s for VDA measurement [ concentration of vitamin D2 , vitamin D3 , 25(OH)D2 , and 25(OH)D3 ] at 2 wk and 2 mo postpartum . A linear mixed model was used to compare breast-milk VDA between the 3 study groups . RESULTS A total of 75 women provided breast-milk sample s ( 44 women provided breast-milk sample s at both 2 wk and 2 mo postpartum ) . The mean ( 95 % CI ) VDA at age 2 wk was 52 IU/L ( 12 , 217 IU/L ) in the placebo group , 51 IU/L ( 17 , 151 IU/L ) in the 1000-IU group , and 74 IU/L ( 25 , 221 IU/L ) in the 2000-IU group ; and at age 2 mo , the mean ( 95 % CI ) VDA was 45 IU/L ( 16 , 124 IU/L ) , 43 IU/L ( 18 , 103 IU/L ) , and 58 IU/L ( 15 , 224 IU/L ) , respectively . There was no significant interaction in VDA between the sample - collection time and treatment ( P = 0.61 ) , but there was a difference between lower- and higher-dosage treatment groups ( P = 0.04 ) . CONCLUSION Maternal vitamin D supplementation during pregnancy of 2000 IU/d ( compared with 1000 IU/d and with a placebo ) results in a higher VDA of breast milk ≥2 mo postpartum . This trial was registered at the Australian New Zeal and Clinical Trials Registry as ACTRN12610000483055
Meta-analyses of r and omized controlled trials ( RCTs ) document that physiological vitamin D supplementation during pregnancy is safe and improves vitamin D and calcium status , thereby protecting skeletal health .
Although certain RCTs and /or meta-analyses reported some other beneficial effects , it is still not clear whether vitamin D supplementation  improves fertility or decreases the risk of adverse pregnancy outcomes such as low birth weight , pre-eclampsia and neonatal mortality , or reduces wheeze/asthma in the infants .
Vitamin D deficiency is common and there exists a huge gap between recommended dietary vitamin D intakes and the poor vitamin D supply in the general population .
While vitamin D is important for musculoskeletal health , there are accumulating data suggesting that vitamin D may also be important for fertility , pregnancy outcomes and lactation .
Significant changes in vitamin D metabolism during pregnancy such as increased production of the " active vitamin D hormone " calcitriol support the important role of vitamin D in this setting .
Observational studies show that vitamin D deficiency is a risk marker for reduced fertility and various adverse pregnancy outcomes and is associated with a low vitamin D content of breast milk .
Nevertheless , vitamin D supplementation in pregnant women is frequently required to achieve a sufficient vitamin D status as recommended by nutritional vitamin D guidelines .