Overall, when these studies are considered together with the findings of the BEST-D trial, they suggest that the dose and timing of vitamin D administration, the prevalence of vitamin D deficiency, age of study participants and scheduling of hepcidin measurements after supplementation with vitamin D should be considered in the trial design when determining the effects of vitamin D on blood levels of hepcidin and other markers of Fe status in healthy adults. This evidence concerns the gene HAMP and vitamin D deficiency.