Beta-carotene and other carotenoid pigments found in darkly colored vegetables are metabolized by the body into vitamin A. Vitamin A, or retinol, is an important nutrient for vision, the immune system and gene expression during development. A vitamin A deficiency can impair development in children, cause eye and skin problems and decrease immune system functions. Children are at higher risk for severe effects from vitamin A deficiency.
About Vitamin A
The carotenoid pigments from which vitamin A is synthesized are mostly fat soluble, and they're best absorbed by the body after they've been cooked and when they're consumed along with a dietary fat. A deficiency in vitamin A can be caused by a prolonged dietary deficiency or by a disorder that interferes with processing and storage, such as liver disease.
Deficiency and Vision
The retina is the thin sheet of cells on the back of the eye that allows you to detect light for vision. Vitamin A is used to produce the pigment that allows the photoreceptors to convert light into a signal the brain can understand. Low vitamin A levels lead to poor dark vision and can eventually cause dryness and scarring of other parts of the eye. Vitamin A deficiency is the leading cause of childhood blindness.
Deficiency and Immunity
Vitamin A is required for the normal functioning of the immune system. A deficiency impairs the barrier function of the skin and the cells lining the airway, causing them to let bacteria and viruses into the body. Vitamin A is also involved in the maturation and development of white blood cells to combat infections that enter the body. Vitamin A deficiency increases the incidence and severity of infections, leading to even further decreases in vitamin A.
Deficiency and Development
Both a deficiency and an excess of vitamin A are known to cause birth and developmental defects. Vitamin A functions in limb development the and formation of the heart, eyes and ears in the fetus. The regulation of growth hormone and the differentiation of stem cells is controlled by vitamin A, and it is especially critical as a child is growing.
Vitamin A in Foods
Children require 1,300 to 2,000 IU of vitamin A daily, while adults require 2,300 to 3,000 IU to maintain good health. Requirements are higher during pregnancy and while breastfeeding. Vitamin A is commonly found in multivitamins and green leafy vegetables such as spinach, broccoli and kale, as well as in yellow and orange vegetables such as squash, carrots, pumpkins and sweet potatoes. Milk, eggs and some cereals are fortified with vitamin A.
Toxicity
Vitamin A can be harmful when taken in very large amounts. The problem is only caused by the direct ingestion of vitamin A from supplements, not from the consumption of carotenoid-rich foods. Symptoms include dry skin, headache, nausea, cerebral edema and bone or joint pain. Toxicity is seen in daily consumption in excess of 10 times the recommended daily dose, or upwards of 25,000 IU, although some populations may be at higher risk.
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