The difference between vitamin D3 and AD is that the ingredients are different, the function is different, and the way of absorption is different. 1. Different components: vitamin D3 is a single component, only vitamin D. Vitamin AD is composed of two vitamins, vitamin A and vitamin D, which can supplement vitamin A and vitamin D. Vitamin D3 can promote calcium and phosphorus metabolism, which is conducive to the normal development of bones. 2. Different roles: Vitamin D3 can promote calcium and phosphorus metabolism, which is conducive to the normal development of bones, and can prevent osteoporosis, rickets and so on. Vitamin A in vitamin AD for human vision function and epithelial system-related functions, has an important regulatory role. 3. Absorption is different: vitamin D3 can directly promote the human intestinal absorption and utilization of calcium and phosphorus, vitamin D in vitamin AD has to be converted in order to play a role in promoting calcium absorption. It is recommended to take vitamin D3 and vitamin AD under the guidance of a professional doctor, do not take blindly.