1 and vitamin D3 can promote the absorption of calcium in intestine, induce the deposition of calcium and phosphorus in bones and prevent rickets. Because the human body can synthesize vitamin D3 by itself, a cholesterol contained in human skin will become vitamin D3 after sunlight.

2. Vitamin D3 has physiological function and can promote the absorption of calcium. However, vitamin D3 is not the final active form in the body. It needs to be converted into active form by enzymes in the liver and kidney, thus promoting the absorption of calcium. Therefore, if the patient's liver or kidney function is abnormal, it is necessary to take the active form of vitamin D3 directly, that is, calcitriol.