Vitamin A is also an indispensable vitamin for human body, it has many functions: 1, vitamin A in the retina rod cells and optic protein synthesis of retinas and optic cyanoplasm, sensitive to low light, in the dark when seeing things, therefore, lack of it causes night blindness; 2, to protect the integrity and soundness of epithelial tissue structure, lack of skin and mucous membrane keratinization; 3, to promote the development of bones and teeth; 4, has to promote the immune organs The current application of vitamin AD preparations, the ratio of vitamin A and vitamin D is 3 to 1. One AD pill contains 1,500 units of vitamin A and 500 units of vitamin D. The amount of vitamin A prophylaxis for infants and children is 1000 to 1300 units. Adverse reactions are only experienced if 50,000 units of vitamin A (about 40 times the equivalent preventive amount) are taken over a long period of time. Therefore, it is safe to take vitamin AD pills, and vitamin D pills alone, which cause vitamin A deficiency, will be detrimental to the healthy development of infants and children.