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 and Testosterone in Healthy Men: A Randomized Controlled Trial
Context : Available evidence shows an association of vitamin D with and rogen levels in men . However , results from preliminary r and omized controlled trials ( RCTs ) are conflicting . Objective : To evaluate whether vitamin D supplementation increases total testosterone ( TT ) levels in healthy men . Design : The Graz Vitamin D&TT‐ RCT is a single‐center , double‐blind , r and omized , placebo‐controlled trial conducted between December 2012 and January 2017 . Setting : Endocrine outpatient clinic at the Medical University of Graz , Austria . Participants : Ninety‐eight healthy men with TT levels ≥10.4 nmol/L and 25‐hydroxyvitamin D [ 25(OH)D ] levels < 75 nmol/L completed the study . Intervention : Subjects were r and omly assigned to receive 20,000 IU/wk of vitamin D3 ( n = 50 ) or placebo ( n = 50 ) for 12 weeks . Main Outcome Measures : Primary outcome was TT measured using mass spectrometry . Secondary outcomes were free testosterone , sex hormone‐binding globulin , estradiol , follicle‐stimulating hormone , and luteinizing hormone levels ; free and rogen index ; metabolic characteristics ; and body composition . Results : In healthy men [ mean values ± st and ard deviation : age , 39 years ( ±13 years ) ; 25(OH)D level , 53.3 nmol/L ( ±18.3 nmol/L ) ; TT , 19.1 nmol/L ( ±5.6 nmol/l ) ] , no significant treatment effect on TT was found ; however , there were significant effects on quantitative insulin sensitivity check index ( QUICKI ) and a trend toward decreased Matsuda index . In the treatment group , median ( interquartile range ) changes for TT , QUICKI , and Matsuda index were 0.5 nmol/L ( −0.63 to 0.63 nmol/L ; P = 0.497 ) , −0.02 ( −0.04 to 0.01 ; P = 0.034 ) , and −0.9 ( −3.2 to 0.8 ; P = 0.051 ) , respectively . Conclusion : Vitamin D treatment had no effect on TT levels in middle‐aged healthy men with normal baseline TT , but it significantly decreased QUICKI . Additional studies investigating vitamin D effects on TT and insulin sensitivity in healthy men are required
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 .