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 .
Hormonal Contraceptive Use Is Associated With Higher Total but Unaltered Free 25-Hydroxyvitamin D Serum Concentrations
Context Intake of hormonal contraceptives ( HC ) is associated with higher total 25-hydroxyvitamin D [ 25(OH)D ] concentrations , but the effect of HC on free 25(OH)D is unclear . Objective We investigated whether free 25(OH)D concentrations differ according to use of HC . Design This is a post hoc analysis of a r and omized open trial . Setting This study was conducted from 13 January to 9 May , 2016 , at a clinical research organization in Esslingen , Germany . Participants We included 201 apparently healthy women of childbearing age . Intervention Participants were r and omly assigned to receive a daily multimicronutrient supplement for 8 weeks ; the supplement contained 200 IU ( n = 100 ) or 800 IU ( n = 101 ) of vitamin D3 . Main Outcome Measures Primary outcome was the difference in free 25(OH)D between users and nonusers of  HC  . Results Overall , 176 participants [ median ( 25th to 75th percentiles ) age : 25 ( 22 to 29 ) years ] with available free 25(OH)D were included in the present analysis . At baseline , total 25(OH)D was significantly higher in users ( n = 110 ) than in nonusers ( n = 66 ) of HC [ 49.2 ( 33.4 to 63.4 ) vs 39.1 ( 23.8 to 52.5 ) nmol/L ; P < 0.001 ] , whereas there was no difference in free 25(OH)D [ 7.87 ( 6.50 to 10.11 ) vs 7.88 ( 6.35 to 10.12 ) pmol/L ; P = 0.923 ] . These results were confirmed after multimicronutrient supplementation and in subgroups according to treatment allocation . Conclusions Use of HC was associated with , on average , 26 % higher total 25(OH)D , whereas free 25(OH)D values did not differ according to use of HC . These findings are relevant for epidemiological studies , but the physiological implication s remain to be clarified
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 .