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 .
Vitamin D intake is inversely associated with rheumatoid arthritis: results from the Iowa Women's Health Study.
OBJECTIVE Vitamin D is a potent regulator of calcium homeostasis and may have immunomodulatory effects . The influence of vitamin D on human autoimmune disease has not been well defined . The purpose of this study was to evaluate the association of dietary and supplemental vitamin D intake with rheumatoid arthritis ( RA ) incidence . METHODS We analyzed data from a prospect i ve cohort study of 29,368 women of ages 55 - 69 years without a history of RA at study baseline in 1986 . Diet was ascertained using a self-administered , 127-item vali date d food frequency question naire that included supplemental vitamin D use . Risk ratios ( RRs ) and 95 % confidence intervals ( 95 % CIs ) were estimated using Cox proportional hazards regression , adjusting for potential confounders . RESULTS Through 11 years of followup , 152 cases of RA were vali date d against medical records . Greater intake ( highest versus lowest tertile ) of vitamin D  was inversely associated with risk of RA ( RR 0.67 , 95 % CI 0.44 - 1.00 , P for trend = 0.05 ) . Inverse associations were apparent for both dietary ( RR 0.72 , 95 % CI 0.46 - 1.14 , P for trend = 0.16 ) and supplemental ( RR 0.66 , 95 % CI 0.43 - 1.00 , P for trend = 0.03 )  vitamin D.  No individual food item high in vitamin D content and /or calcium was strongly associated with RA risk , but a composite measure of milk products was suggestive of an inverse association with risk of RA ( RR 0.66 , 95 % CI 0.42 - 1.01 , P for trend = 0.06 ) . CONCLUSION Greater intake of vitamin D may be associated with a lower risk of RA in older women , although this finding is hypothesis generating
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 .