The fact that most MAs on results from RCTs did not show a beneficial effect does not disprove the hypothesis suggested by observational findings on adverse health outcomes of low 25OHD levels
Background A large number of observational studies have reported harmful effects of low 25-hydroxyvitamin D ( 25OHD ) levels on non-skeletal outcomes .
We performed a systematic quantitative review on characteristics of r and omized clinical trials ( RCTs ) included in meta-analyses ( MAs ) on non-skeletal effects of vitamin D supplementation .
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 fact that most MAs on results from RCTs did not show a beneficial effect does not disprove the hypothesis suggested by observational findings on adverse health outcomes of low 25OHD levels
Background A large number of observational studies have reported harmful effects of low 25-hydroxyvitamin D ( 25OHD ) levels on non-skeletal outcomes .
We performed a systematic quantitative review on characteristics of r and omized clinical trials ( RCTs ) included in meta-analyses ( MAs ) on non-skeletal effects of vitamin D supplementation .