Vitamin D₃, with different dosage requirements for different ages and needs, has a preventive dosage between 400-800 units per day depending on the population. The Chinese Nutrition Association (CNA) recommends the following daily preventive doses of vitamin D₃: preterm infants, twins, and low-birth-weight infants: 800 units from zero to three months; after three months, 400 units; infants under one year of age, 400 units; over one year of age and up to the teenage years, 600 units; adults, 400 units; the elderly and post-menopausal women can increase to 600 units. The main role of vitamin D₃ is to promote the absorption of calcium and phosphorus in the gastrointestinal tract, and to prevent and treat rickets. The therapeutic dose needs to be based on the level of vitamin D₃ in the blood and a combination of other laboratory findings. It is contraindicated in patients with hypercalcemia, hyperphosphatemia and renal rickets. Large quantities may cause poisoning. Please take Vitamin D₃ under the guidance of a doctor.