Mean serum 25-hydroxyvitamin D concentrations by treatment group. The mean serum 25-OHD concentrations of the groups receiving standard-dose (12 000 IU/mo) and high-dose (100 000 IU/mo) vitamin D₃ did not differ statistically at baseline and rose to plateau at different levels at 3-4 months; overall mean concentration during the 2-year treatment period was significantly higher in the high-dose group (36.1 ng/mL) compared with the standard-dose group (19.1 ng/mL; P < .001). Error bars indicate SEM.