The main components of cod liver oil are vitamin A and D. Vitamin A is mainly used for the prevention of night blindness, and vitamin D can avoid the occurrence of rickets, and it is recommended that newborn babies can start taking cod liver oil after birth. Cod liver oil is mainly extracted from the liver of deep-sea fish in the fat oil, in which vitamin A can maintain the integrity of the mucosal epithelium, promote growth and development, regulate and stabilize the function of the immune system. Vitamin D can mineralize bone, participate in immune regulation, promote cell proliferation, differentiation and apoptosis. If infants are deficient in vitamins A and D, the development of intelligence, eyesight and bones can be seriously affected, and immunity is easy to be low, thus suffering from a variety of infectious diseases. Therefore, it is recommended that newborns be supplemented with cod liver oil under the guidance of a doctor. It is usually recommended that infants and young children continue to take cod liver oil supplements until they are about 2 years old because of their rapid growth and development, and cod liver oil can promote calcium absorption and prevent rickets.