However, to prevent toxicity, it is important not to exceed the maximum tolerable intake level (UL) of 10,000 IU (3000 mcg) per day for adults (2.A healthy, varied diet will provide most people with enough vitamin A. If you're interested in the antioxidant properties of vitamin A, food sources are the best. It's unclear if vitamin A supplements offer the same benefits as antioxidants found naturally in foods. Too much vitamin A can be harmful, and too much vitamin A during pregnancy has been linked to birth defects.
Conditions that interfere with normal digestion can result in poor absorption of vitamin A, such as celiac disease, Crohn's disease, cirrhosis, alcoholism, and cystic fibrosis. The total vitamin A content of a food is usually expressed in micrograms (µg) of retinol equivalents (RE). Many people are also unaware that the recommended daily allowance (RDA) of vitamin A varies depending on how it is consumed. Vitamin A is also fat-soluble, meaning that any amount that the body doesn't need immediately is absorbed and stored in adipose tissue or liver.
Vitamin A can't give you superpowers for night vision or cure your dependence on contact lenses, but eating an adequate amount will promote eye health. The main nutrient in carrots, beta-carotene (responsible for the characteristic orange color of this tuber), is a precursor to vitamin A and helps the eyes adapt when there is little light. Vitamin A, found in many dietary supplements, is known to promote eye function, tissue growth, and bone, reproductive, and immune function. Studies on age-related eye diseases (AREDS), funded by the NIH, found that daily intake of high doses of vitamins, including vitamins C and E, lutein, and zeaxanthin, delayed the progression of intermediate and late-stage AMD, especially in participants who consumed the lowest amounts of carotenoids.
Vitamin A also stimulates the production and activity of white blood cells, participates in bone remodeling, helps keep endothelial cells (those that line the inner surfaces of the body) healthy, and regulates cell growth and division to the extent necessary for reproduction. He found that higher blood levels of alphacarotene (a form of vitamin A that includes lutein and zeaxanthin) were associated with better cognition (for example, in addition to being used as an oral supplement, vitamin A is used in topical creams to reduce fine wrinkles, blemishes, and roughness and treat acne). As an oral supplement, vitamin A primarily benefits people who have a poor or limited diet or who have a condition that increases the need for vitamin A, such as pancreatic disease, eye disease, or measles. The One A Day's Women's Multivitamin Complex, for example, contains 4000 IU of vitamin A, 50% in the form of beta-carotene.
The two main forms of vitamin A in the human diet are preformed vitamin A (retinol, retinyl esters) and provitamin A carotenoids, such as alpha-carotene and beta-carotene, which are converted to retinol.
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