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 .
Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey.
BACKGROUND Recent studies suggest a role for vitamin D in innate immunity , including the prevention of respiratory tract infections ( RTIs ) . We hypothesize that serum 25-hydroxyvitamin D ( 25[OH]D ) levels are inversely associated with self-reported recent upper RTI ( URTI ) . METHODS We performed a secondary analysis of the Third National Health and Nutrition Examination Survey , a probability survey of the US population conducted between 1988 and 1994 . We examined the association between 25(OH)D level  and  recent URTI in 18 883 participants 12 years and older . The analysis adjusted for demographics and clinical factors ( season , body mass index , smoking history , asthma , and chronic obstructive pulmonary disease ) . RESULTS The median serum 25(OH)D level was 29 ng/mL ( to convert to nanomoles per liter , multiply by 2.496 ) ( interquartile range , 21 - 37 ng/mL ) , and 19 % ( 95 % confidence interval [ CI ] , 18%-20 % ) of participants reported a recent URTI . Recent URTI was reported by 24 % of participants with 25(OH)D levels less than 10 ng/mL , by 20 % with levels of 10 to less than 30 ng/mL , and by 17 % with levels of 30 ng/mL or more ( P < .001 ) . Even after adjusting for demographic and clinical characteristics , lower 25(OH)D levels were independently associated with recent URTI ( compared with 25[OH]D levels of > or = 30 ng/mL : odds ratio [ OR ] , 1.36 ; 95 % CI , 1.01 - 1.84 for < 10 ng/mL and 1.24 ; 1.07 - 1.43 for 10 to < 30 ng/mL ) . The association between 25(OH)D level and URTI seemed to be stronger in individuals with asthma and chronic obstructive pulmonary disease ( OR , 5.67 and 2.26 , respectively ) . CONCLUSIONS Serum 25(OH)D levels are inversely associated with recent URTI . This association may be stronger in those with respiratory tract diseases . R and omized controlled trials are warranted to explore the effects of vitamin D supplementation on RTI
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 .