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 .
Effect of Two Different Multimicronutrient Supplements on Vitamin D Status in Women of Childbearing Age: A Randomized Trial
The German Nutrition Society raised in 2012 the recommended daily vitamin D intake from 200 to 800 international units ( IU ) to achieve 25-hydroxyvitamin D ( 25(OH)D ) levels of at least 50 nmol/L , even when endogenous vitamin D synthesis is minimal such as in winter . We aim ed to evaluate this recommendation in women of childbearing age . This is a single-center , r and omized , open trial conducted from 8 January to 9 May 2016 in Esslingen , Germany . We r and omized 201 apparently healthy women to receive for 8 weeks a daily multimicronutrient supplement containing either 200 IU ( n = 100 ) or 800 IU vitamin D3 ( n = 101 ) . Primary outcome measure was serum 25(OH)D.  196 participants completed the trial .  Increases in 25(OH)D ( median with interquartile range ) from baseline to study end were 13.2 ( 5.9 to 20.7 ) nmol/L in the 200 IU group , and 35.8 ( 18.2 to 52.8 ) nmol/L in the 800 IU group ( p < 0.001 for the between group difference ) . At study end , levels of ≥50 nmol/L were present in 70.4 % of the 200 IU group and in 99 % of the 800 IU group . Participants on hormonal contraceptives had higher baseline levels and a stronger increase in 25(OH)D. In conclusion , daily supplementation of 800 IU vitamin D3 during wintertime in Germany is sufficient to achieve a 25(OH)D level of at least 50 nmol/L in almost all women of childbearing age , whereas 200 IU are insufficient
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 .