Efficacy of different doses and time intervals of oral vitamin D supplementation with or without calcium in elderly nursing home residents: reply to comment by Vieth

Abstract

Dear Editors, We have read the comments of Dr. Vieth with interest. We agree that the dosing interval does not need to be much shorter than the circulating half-life of 25(OH)D, anywhere between 10 days and 2 months, according to different assessments [1, 2]. The difference between the daily and weekly dose with regard to serum 25(OH)D was significant but not clinically relevant. However, the difference between these doses and the monthly dose is clinically relevant with regard to serum 25(OH)D and serum PTH. In any case, the mechanism of the effect of an increase of serum 25(OH)D on serum PTH is a complex question, and different effects according to different dosing intervals cannot be ruled out. The compliance in our study was high as the nurses distributed the medication and supervised the ingestion. Our study was not a rigorous pharmacological study; however, it simply demonstrates that results of vitamin D supplementation do not solely depend on the cumulative dose.