ABSTRACT
Vitamin A in the form of retinol is essential for vision, growth, and differentiation of epithelial tissue, and is required for bone growth, immunity, reproduction, and embryonic development. Pre-formed vitamin A as retinol is obtained from animal sources such as liver, butter, cheese, margarine, dried milk, cream, fortified milk, kidney, and some seafoods. Preterm infants are generally considered to be at risk for vitamin A deficiency because their plasma retinol concentrations are usually lower than those of term infants, children, or adults. Serum vitamin A and retinol-binding protein concentrations are lower in patients with diabetes mellitus than those of non-diabetic control subjects. Inadequate intakes of vitamin A, either as preformed retinol or as active carotenoids, result in a tissue decrease of the vitamin. Retinol can be measured in serum or plasma with the use of microtechniques that employ either fluorometric, spectrophotometric, trifluoracetic acid colorimetric, or high performance liquid chromatographic procedures.
