Vitamin AD is a multivitamin that contains both vitamin A and vitamin D; whereas vitamin D contains only vitamin D, a single component. Although both vitamin AD and vitamin D are vitamins, they are distinct. Vitamin AD can promote the absorption of both vitamin A and vitamin D. It can promote the development of skin and epithelial tissues, as well as promote bone development and prevent poor bone growth. Vitamin AD has a role in the prevention and treatment of night blindness, rickets, pediatric hand and foot convulsions and other diseases. Vitamin D promotes the body’s absorption of calcium, phosphorus and other trace elements, and has a role in the prevention and treatment of symptoms brought on by vitamin D deficiency (such as pediatric rickets). Therefore, many calcium supplements include vitamin D, which can promote the body’s ability to absorb calcium. Overall, the effects of vitamin AD will be a little more comprehensive than the effects of vitamin D. Both of these vitamin supplements should be served with medical advice, and taking too much may cause risks such as poisoning.