Toxicity Sources

"Vitamin A toxicity, or hypervitaminosis A, is rare. Typically it requires you to ingest ten times the RDA of preformed vitamin A in the form of supplements—it would be hard to consume such high levels from a regular diet—for a substantial amount of time, although some people may be more susceptible to vitamin A toxicity at lower doses. The signs and symptoms of vitamin A toxicity include dry, itchy skin, loss of appetite, swelling of the brain, and joint pain. In severe cases, vitamin A toxicity may cause liver damage and coma. Vitamin A is essential during pregnancy, but doses above 3,000 micrograms per day, or 10,000 international units, have been linked to an increased incidence of birth defects. Pregnant women should check the amount of vitamin A contained in any prenatal or pregnancy multivitamin she is taking to assure the amount is below the UL. There is more than one source of vitamin A in the diet. There is preformed vitamin A, which is abundant in many animal-derived foods, and there are carotenoids, which are found in high concentrations in vibrantly colored fruits and vegetables and some oils. Some carotenoids are converted to retinol in the body by intestinal cells and liver cells. However, only minuscule amounts of certain carotenoids are converted to retinol, meaning fruits and vegetables are not necessarily good sources of vitamin A. The RDA for vitamin A includes all sources of vitamin A and is given in micrograms of retinol activity equivalents (RAE) to take into account the many different forms it is available in. The human body converts all dietary sources of vitamin A into retinol. Therefore, 1 microgram of retinol is equivalent to 12 micrograms of beta-carotene, and 24 micrograms of alpha-carotene or beta-cryptoxanthin. For example, 12 micrograms of fruit- or vegetable-based beta-carotene will yield 1 microgram of retinol. Current vitamin A listings in food and on supplement labels use international units (IUs): 1 IU retinol equals 0.3 micrograms RAE; 1 IU beta-carotene from dietary supplements equals 0.15 micrograms RAE; 1 IU beta-carotene from food equals 0.05 micrograms RAE; and 1 IU alpha-carotene or beta-cryptoxanthin equals 0.025 micrograms RAE. The RDA for vitamin A is considered sufficient to support growth and development, reproduction, vision, and immune system function while maintaining adequate stores, which are good for four months, in the liver. The RDA and UL are as follows: infants 0–6 months, 400 micrograms RAE per day as adequate intake and a 600 microgram UL; infants 7–12 months, 500 micrograms as adequate intake and a 600 microgram UL; children 1–3 years, 300 micrograms RAE and a 600 microgram UL; children 4–8 years, 400 micrograms and a 900 microgram UL; children 9–13 years, 600 micrograms and a 1,700 microgram UL; adolescent males 14–18 years, 900 micrograms and a 2,800 microgram UL; adolescent females 14–18 years, 700 micrograms and a 2,800 microgram UL; adult males over 19 years, 900 micrograms and a 3,000 microgram UL; and adult females over 19 years, 700 micrograms and a 3,000 microgram UL. Preformed vitamin A is found only in foods from animals, with the liver being the richest source because that is where vitamin A is stored. Beef liver provides 27,185 IU per 3-ounce serving, chicken liver provides 12,325 IU per 3-ounce serving, skim milk provides 500 IU per cup, whole milk provides 249 IU per cup, and cheddar cheese provides 284 IU per ounce."