Vitamin D works primarily to promote calcium absorption and strengthen bones. Vitamin D is a fat-soluble vitamin that regulates calcium and phosphorus metabolism and promotes the absorption of calcium and phosphorus by cells in the small intestine, thereby promoting bone calcification and increasing bone density. Vitamin D is also an immunomodulator, when the body’s immune function is in a state of inhibition, vitamin B3 can enhance the function of monocytes and macrophages, thus improving immunity. Therefore, vitamin D is mainly used for the prevention and treatment of osteoporosis, chronic hypocalcemia, hypophosphatemia, and rickets in clinical practice. Infants and young children, pregnant women, the elderly need to follow the doctor’s advice to supplement vitamin D to prevent vitamin D deficiency diseases. However, it is not recommended for patients with the presence of urinary stones, osteosclerosis and other diseases.