Vitamin D is not a calcium supplement, although it is often used together with calcium preparations, but vitamin D and calcium preparations are two different drugs. Vitamin D is a fat-soluble vitamin, a vitamin drug whose main role is to promote the body’s absorption of calcium and also phosphorus. Vitamin D regulates the balance of calcium and phosphorus in the body, keeping the calcium and phosphorus concentrations in the blood within normal limits. Vitamin D is also involved in parathyroid-related functions and regulates the level of calcitonin in the body, allowing calcium to be deposited on newly formed bones and facilitating bone tissue recovery and reconstruction. Vitamin D can be used clinically for a variety of reasons for inadequate intake of the vitamin, such as reduced vitamin D levels due to inadequate food intake or liver or kidney disease. It is important to note that vitamin D supplementation is not required if the patient has hypercalcemia, hypercalciuria, or if the body has a relatively high level of vitamin D itself.