Vitamin AD and vitamin D3 are generally recommended until the age of 2 to 3 years, after 3 years of age the body is still deficient, you can continue to supplement, and there is no specific length of time to take the medication. Vitamin A and vitamin D are more deficient in infants and young children, and it is sufficient to supplement one of them or take them alternately as prescribed by the doctor. Usually in the birth of 1 ~ 2 weeks to start supplementation, on the development of the nervous system, bone development, immunity to improve the role of the general recommendation of the routine to eat until the age of 2 ~ 3 years. If your baby is still deficient in vitamin A or vitamin D after the age of 3, you can continue to supplement, and there is no absolute stopping time. Vitamin AD and Vitamin D3 should be taken under the supervision of a doctor, and the specific dosage time should also follow the doctor’s instructions.