Smaller concentration‐supplementation slopes at a higher vitamin D treatment dose

There are conflicting reports regarding serum 25‐hydroxyvitamin D [25(OH)D total] concentration slope increases at different vitamin D 3 supplementation doses. The purpose of this study was to normalize serum 25(OH)D concentration increases to different vitamin D 3 supplementation doses. A prospective, double‐blind, placebo controlled study was conducted in healthy adults (23–43 years). Twenty‐two subjects were randomized to one of three groups: vitamin D 3 supplementation at (1) 200 IU (n = 7) or (2) 4000 IU (n = 7), or (3) a matching placebo (n = 8). Supplements were taken daily for 28 days during the winter season (latitude ≈40° N). Serum 25(OH)D concentrations were measured in fasting blood draw samples obtained prior to and 7‐, 14‐, 21‐ and 28‐d after supplementation. Serum 25(OH)D concentrations increased 21‐d (P < 0.001) after 200 IU and 7‐d (P < 0.001) after 4000 IU of vitamin D 3 supplementation. Following supplementation, serum 25(OH)D concentrations were greater in the 4000 IU compared to the 200 IU (P < 0.05) and placebo (P < 0.05) groups. The concentration‐supplementation dose slopes (ng/ml/100 IU) were greater (P < 0.05) following 200 IU compared to 4000 IU of vitamin D 3 . In conclusion, serum 25(OH)D concentration increases were greater but concentration‐dose slopes were lower at a higher vitamin D 3 supplementation dose. Sources of support: Deseret Foundation, UT and USANA Health Sciences, Inc., UT