The evidence shows that vitamin D supplementation provides some benefit in fracture prevention ( likely ∼10–15 % relative reduction ) , particularly at a dose ≥800 IU and with calcium ; a likely benefit in the rate of falls , though it is less clear whether the number of fallers changes ; and a possible small ( ∼5 % ) relative reduction in mortality .
Evidence does not support the use of vitamin D supplementation for the prevention of cancer , respiratory infections or rheumatoid arthritis .
Similarly , evidence does not support vitamin D supplementation for the treatment of multiple sclerosis and rheumatoid arthritis or for improving depression/mental well-being .
Regular testing of 25-hydroxyvitamin D is generally not required , and mega-doses ( ≥300,000 IU ) appear to increase harms .
Over the past decade , a large body of observational evidence has suggested an association between  lower vitamin D status ( 25-hydroxyvitamin D ) and multiple acute and chronic disorders , including cancer , multiple sclerosis , depression and respiratory tract infections .
This evidence has fostered the hypothesis that increasing vitamin D intake may treat and prevent such disorders .
Our objective was to perform a critical analysis of the highest-level evidence for ten common beliefs regarding vitamin D for the prevention of falls , fractures and respiratory tract infections , the reduction of cancer incidence/mortality and overall mortality , and the prevention or treatment of depression/mental well-being , rheumatoid arthritis and multiple sclerosis , as well as maximum dosing and regular testing .
Effect of vitamin D3 supplementation on upper respiratory tract infections in healthy adults: the VIDARIS randomized controlled trial.
CONTEXT Observational studies have reported an inverse association between serum 25-hydroxyvitamin D ( 25-OHD ) levels and incidence of upper respiratory tract infections ( URTIs ) . However , results of clinical trials of vitamin D supplementation have been inconclusive . OBJECTIVE To determine the effect of vitamin D supplementation on incidence and severity of URTIs in healthy adults . DESIGN , SETTING , AND PARTICIPANTS R and omized , double-blind , placebo-controlled trial conducted among 322 healthy adults between February 2010 and November 2011 in Christchurch , New Zeal and . INTERVENTION Participants were r and omly assigned to receive an initial dose of 200,000 IU oral vitamin D3 , then 200,000 IU 1 month later , then 100,000 IU monthly ( n = 161 ) , or placebo administered in an identical dosing regimen ( n = 161 ) , for a total of 18 months . MAIN OUTCOME MEASURES The primary end point was number of URTI episodes . Secondary end points were duration of URTI episodes , severity of URTI episodes , and number of days of missed work due to URTI episodes . RESULTS The mean baseline 25-OHD level of participants was 29 ( SD , 9 ) ng/mL. Vitamin D supplementation result ed in an increase in serum 25-OHD levels that was maintained at greater than 48 ng/mL throughout the study . There were 593 URTI episodes in the vitamin D group and 611 in the placebo group , with no statistically significant differences in the number of URTIs per participant ( mean , 3.7 per person in the vitamin D group and 3.8 per person in the placebo group ; risk ratio , 0.97 ; 95 % CI , 0.85 - 1.11 ) , number of days of missed work as a result of URTIs ( mean , 0.76 days in each group ; risk ratio , 1.03 ; 95 % CI , 0.81 - 1.30 ) , duration of symptoms per episode ( mean , 12 days in each group ; risk ratio , 0.96 ; 95 % CI , 0.73 - 1.25 ) , or severity of URTI episodes . These findings remained unchanged when the analysis was repeated by season and by baseline 25-OHD levels . CONCLUSION In this trial , monthly administration of 100,000 IU of vitamin D did not reduce the incidence or severity of URTIs in healthy adults . TRIAL REGISTRATION anzctr.org.au Identifier : ACTRN12609000486224
The evidence shows that vitamin D supplementation provides some benefit in fracture prevention ( likely ∼10–15 % relative reduction ) , particularly at a dose ≥800 IU and with calcium ; a likely benefit in the rate of falls , though it is less clear whether the number of fallers changes ; and a possible small ( ∼5 % ) relative reduction in mortality .
Evidence does not support the use of vitamin D supplementation for the prevention of cancer , respiratory infections or rheumatoid arthritis .
Similarly , evidence does not support vitamin D supplementation for the treatment of multiple sclerosis and rheumatoid arthritis or for improving depression/mental well-being .
Regular testing of 25-hydroxyvitamin D is generally not required , and mega-doses ( ≥300,000 IU ) appear to increase harms .
Over the past decade , a large body of observational evidence has suggested an association between  lower vitamin D status ( 25-hydroxyvitamin D ) and multiple acute and chronic disorders , including cancer , multiple sclerosis , depression and respiratory tract infections .
This evidence has fostered the hypothesis that increasing vitamin D intake may treat and prevent such disorders .
Our objective was to perform a critical analysis of the highest-level evidence for ten common beliefs regarding vitamin D for the prevention of falls , fractures and respiratory tract infections , the reduction of cancer incidence/mortality and overall mortality , and the prevention or treatment of depression/mental well-being , rheumatoid arthritis and multiple sclerosis , as well as maximum dosing and regular testing .