Approximately 10,000 IUs should be the average adult intake and is a safe amount to consume. The RDA amount will prevent most deficiency symptoms, such as night blindness, but for vitamin A’s antioxidant properties, higher amounts are needed. About 20,000–30,000 IUs daily, preferably as beta-carotene, may be the best range, especially for those of us with some levels of anxiety and stress. If vitamins C and E are used, slightly lower amounts of A are needed, since C and E help prevent the loss of stored vitamin A.
The upper intake, including diet and supplemental vitamin A, ranges from 50,000–100,000 IUs per day for short periods of a week or two. However, these amounts often produce some side effects over time. If no body deficiency or increased body needs of vitamin A are present, 50,000 IUs can cause problems. Infants and children can run into difficulty with doses as low as 10,000–25,000 IUs given over time, depending on their size. This is why it is important to know our food sources and supplement levels of preformed vitamin A (not beta-carotene, which is safe at higher levels), so that we can find the right amounts for each of us and our families.