The demand for vitamin D varies from age to age, from 400 IU per day in infancy, 200 IU per day until the age of 50, 400 IU per day between the ages of 50 and 70, and 600 IU per day above the age of 70. The demand is higher. After entering old age, the intestinal tract of the elderly has fewer vitamin D receptors and the intestinal tract’s ability to absorb vitamin D decreases, so more vitamin D intake is needed to ensure that the amount absorbed is sufficient.