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 .
Calcium and vitamin D supplementation and incident rheumatoid arthritis: the Women’s Health Initiative Calcium plus Vitamin D trial
To determine whether calcium plus vitamin D supplementation ( CaD ) affects incidence of  rheumatoid arthritis ( RA ) . Participants enrolled in the Women ’s Health Initiative CaD trial ( n = 36,282 ) were r and omized to 1,000 mg calcium carbonate plus 400 IU of vitamin D3 daily or to placebo . Incident RA cases were identified via self-report and vali date d rheumatic medication use . Cox proportional hazards models were used to compare RA incidence in the treatment versus placebo groups . The analysis included 32,435 women without the history of RA , of which 163 incident RA cases were identified over an average of 5.1 years . No significant differences in demographics , total personal vitamin D intake [ P = 0.36 ] , or solar irradiance [ P = 0.68 ] were seen between the groups . In intention-to-treat analyses , no differences were observed in RA incidence [ HR 1.04 , 95 % CI 0.76 , 1.41 ] . No significant modifying effects were seen for stratum of age , solar irradiance , or total vitamin D intake , overall or when adjusted for adherence . Significant effect modifications were seen between  CaD  and total vitamin D  intake and CaD and solar irradiance that suggest increased RA incidence with high vitamin D exposure . CaD supplementation did not demonstrate a significant effect on RA incidence  in postmenopausal women . Modifying effects between CaD and both solar irradiance and dietary vitamin D intake are suggestive that multiple high vitamin D exposures may increase RA incidence . Further research is needed to fully explore the benefits and possible adverse effects of vitamin D supplementation on RA
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 .