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 .
Randomized controlled trials of vitamin D and cancer incidence: A modeling study
Although geographic ecological studies and observational studies find that ultraviolet B exposure and 25-hydroxyvitamin D [ 25(OH)D ] concentrations are inversely correlated with 15–20 types of cancer , few r and omized controlled trials ( RCTs ) of vitamin D support those findings . The poor design of some RCTs may account for that lack of support . Most vitamin D RCTs to date have considered the vitamin D dose , rather than initial , final , or changes in , serum 25(OH)D concentrations . Here a model is developed for use in design ing and analyzing vitamin D RCTs with application to cancer incidence . The input variables of the model are  vitamin D dose , baseline and achieved 25(OH)D concentrations , known rates of cancer for the population  , and numbers of participants for the treatment and placebo arms is estimated — vitamin D dosage and numbers of participants are varied to achieve desired hazard ratio significance , using information from two  vitamin D RCTs on cancer incidence conducted in Nebraska with good agreement between the model estimates and reported hazard ratios . Further improvements to the conduct of vitamin D RCTs would be to start the trial with a moderate bolus dose to achieve the desired 25(OH)D concentrations , and bloodspot 25(OH)D assay use in summer and winter annually to monitor seasonal and long-term changes in 25(OH)D concentration and compliance , and to allow dosage adjustment for achievement of desired vitamin D status
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 .