Välimäki VV et al. 2016; 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; Clin. Endocrinol. 84(6):837-44

Study design: Elderly women received 100 000 or 200 000 IU of vitamin D3 or placebo orally every 3 months plus 1 g of calcium daily over one year to test intermittent dosing for improving the adherence of vitamin D therapy, targeting a 25OHD level of 75 nmol/l after baseline.

Results: Serum 25OHD levels increased but in both treated groups only with marginal difference. Approximately half of all measurements of 25OHD in both groups reached the goal of 75 nmol/l.

Conclusions: Both applied dosis regimens are not able to keep 25OHD levels over 75 nmol/l over 1 year. Therefore, shorter dosing intervals between vitamin D3 administrations must be chosen instead of longer ones.