How well are the optimal serum 25OHD concentrations reached in high-dose intermittent vitamin D therapy? a placebo-controlled study on comparison between 100 000 IU and 200 000 IU of oral D3 every 3 months in elderly women.

ObjectiveIntermittent dosing may improve adherence to vitamin D therapy. Dosing regimen should maintain optimal serum 25-hydroxyvitamin D (25OHD) levels over all the year. We compared two dosing regimens, the primary outcome being the percentage of 25OHD measurements reaching the targets of 75 nmol/l or 50 nmol/l after baseline. DesignRandomized, placebo-controlled parallel group comparison. PatientsSixty women aged 750 29 years. Interventions100 000 IU (group 1D) or 200 000 IU (2D) of vitamin D-3 or placebo orally every 3 months plus calcium 1 g daily for 1 year. MeasurementsSerum 25OHD, 1,25-dihydroxyvitamin D, PTH, sclerostin, ionized calcium, urinary calcium, renal function, bone turnover markers. ResultsSerum 25OHD increased, but the difference between two doses was of borderline significance (P = 00554; area under curve analysis). Immediate postadministrative increases were higher in the 2D vs 1D group (P < 005) after 3 and 6 months' dosing. In the 1D and 2D groups, 512% and 577% of all on-treatment measurements reached the target of 75 nmol/l. PTH levels differed marginally (P = 00759) due to tendency to lowering immediately after vitamin D boluses. Urinary calcium differed between the groups (P = 00193) due to increases 1 week after vitamin D dosing. ConclusionsThe doses of 100 000 or 200 000 IU of oral cholecalciferol every 3 months were not capable of stabilizing 25OHD levels over the target of 75 nmol/l over the year. To improve the efficacy of high-dose vitamin D therapy, the interval between boluses has to be shortened instead of increasing their size.