Background and Objectives Vitamin D deficiency is frequent during the winter and occurs throughout the year in the elderly or patients suffering from autoimmune diseases. The objective of this study was to evaluate the pharmacokinetic properties of oral supplementation versus a single intramuscular injection of cholecalciferol in healthy individuals. Research design and methods Up to 8,000 I.U. oral cholecalciferol was administered daily for 84 days in a 4 week dose-escalation setting to vitamin D deficient individuals. In another cohort, a single intramuscular injection of 100,000 I.U. cholecalciferol was given. In both cohorts, individuals without vitamin D intake served as the comparison group. 25-hydroxyvitamin D (25(OH)D) concentrations were measured in all individuals at defined time points throughout the studies. Results The mean 25(OH)D serum concentration increased significantly after oral cholecalciferol intake compared to the control group (day 28: 83.4 nmol/l and 42.5 nmol/l; day 56: 127.4 nmol/l and 37.3 nmol/l; day 84: 159.7 nmol/l and 30.0 nmol/l). In individuals receiving 100,000 I.U. cholecalciferol intramuscular, the mean 25(OH)D serum concentration peaked after 4 weeks measuring 70.9 nmol/l compared to 32.7 nmol/l in the placebo group (p = 0.002). The increase of 25(OH)D serum concentrations after 28 days was comparable between both routes of administration (p = 0.264). Conclusions Oral and intramuscular cholecalciferol supplementation effectively increased serum 25(OH)D concentrations.
