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 .
Standardizing serum 25-hydroxyvitamin D data from four Nordic population samples using the Vitamin D Standardization Program protocols: Shedding new light on vitamin D status in Nordic individuals
Abstract Knowledge about the distributions of serum 25-hydroxyvitamin D ( 25(OH)D ) concentrations in representative population sample s is critical for the quantification of vitamin D deficiency as well as for setting dietary reference values and food-based strategies for its prevention . Such data for the European Union are of variable quality making it difficult to estimate the prevalence of vitamin D deficiency across member states . As a consequence of the widespread , method -related differences in measurements of serum 25(OH)D concentrations , the Vitamin D St and ardization Program ( VDSP ) developed protocol s for st and ardizing existing serum 25(OH)D data from national surveys around the world . The objective of the present work was to apply the VDSP protocol s to existing serum 25(OH)D data from a Danish , a Norwegian , and a Finnish population -based health survey and from a Danish r and omized controlled trial . A specifically-selected subset ( n 100–150 ) of bio-banked serum sample s from each of the studies were reanalyzed for 25(OH)D by LC-MS/MS and a calibration equation developed between old and new 25(OH)D data , and this equation was applied to the entire data -sets from each study . Compared to estimates based on the original serum 25(OH)D data , the percentage vitamin D deficiency ( < 30 nmol/L ) decreased by 21.5 % in the Danish health survey but by only 1.4 % in the Norwegian health survey ; but was relatively unchanged ( 0 % and 0.2 % ) in the Finish survey or Danish RCT , respectively , following VDSP st and ardization . In conclusion , st and ardization of serum 25(OH)D concentrations is absolutely necessary in order to compare serum 25(OH)D concentrations across different study population s , which is needed to quantify and prevent vitamin D deficiency
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 .