Study Design for Vitamin D Randomized Clinical Trials

To the Editor The article by Uusi-Rasi and colleagues¹ raises important considerations in the study design of randomized clinical trials on the effect of vitamin D on falling. It is clear from many randomized clinical trials that the role of vitamin D supplementation on falling—if it has a role—is likely to be found in subsets of the falling population.² It is unfortunate that the study design did not take advantage of previous study findings.