A controlled-release pharmaceutical formulation including cholecalciferol and/or ergocalciferol, a method of making the formulation, and a method of administering the formulation to treat 25-hydroxyvitamin D insufficiency or deficiency, are disclosed. The composition and method of administration preferably result in delayed release of the vitamin(s) in the ileum of the small intestine and sustained, substantially constant, release of the vitamin(s) over an extended period, e.g., at least 4 hours or more. Individual and combined dosages of 500 lU to 50,000 IU per dosage form, preferably daily, are disclosed. The compositions and methods are contemplated to exhibit one or more advantages including, but not limited to efficiency of vitamin D repletion and maintenance； mitigation or avoidance of first pass effects of the Vitamin D compounds on the duodenum； mitigation or avoidance of adverse supraphysiological surges in intralumenal, intracellular and blood levels of cholecalciferol, ergocalciferol and 25- hydroxyvitamin D and their consequences； and mitigation or avoidance of serious side effects associated with Vitamin D supplementation, namely Vitamin D toxicity.
