One year old babies should consume 600 IU/d of vitamin D3. Vitamin D3 is one of the biological regulators of calcium homeostasis in the body. The main sources of vitamin D for infants and young children include food intake and sunlight synthesis. One-year-old babies can consume 600IU/d of vitamin D3 under the guidance of a doctor. 1. Food intake: Natural foods contain little vitamin D, but formula intake is sufficient for vitamin D, and supplementation is generally not necessary. 2. Skin light synthesis: the amount of vitamin D3 produced by the skin is related to the duration of sunlight, wavelength, and the area of exposed skin. Skin light synthesis is the main source of vitamin D for babies. For the prevention of vitamin D deficiency, the key lies in sunbathing and the right amount of vitamin D supplementation. If you find that your baby is deficient in vitamin D, you should go to the hospital for treatment and take vitamin D supplements under your doctor’s supervision.