Vitamin A toxicity is relatively rare. Vitamin A toxicity is called hypervitaminosis A. Toxicity is not caused by provitamin A carotenoids such as beta-carotene. Hypervitaminosis A is caused by over consumption of the kind of preformed vitamin A found in animal products and many supplements. This preformed vitamin A is absorbed quickly and it is slowly eliminated. Toxicity can result from longterm low intakes or from short-term high intakes of preformed vitamin A.
Vitamin Ais transported through the blood bound to protein. Toxicity begins to develop when the binding proteins are all full and free retinol starts to damage cells. Children are more vulnerable to hypervitaminosis A than adults. Normally, toxicity is associated with long-term consumption of vitamin A in excess of 10 times the RDA (8,000 to 10,000 mcg/day or 25,000 to 33,000 IU/day).
People who may be susceptible to toxicity at lower doses include the elderly, pregnant women, and alcoholics. A tolerable upper intake level UL has been set at 3,000 mcg (10,000 IU)/day of preformed vitamin Afor adults and less for children. It is possible to receive excessive vitamin A from the diet. Liver is dangerously high in vitamin A. A diet consisting largely of animal products can cause hypervitaminosis A.
BETA-CAROTENE IS NON-TOXIC
No tolerable upper intake level for beta-carotene has been set because it is nontoxic. Beta-carotene is stored in fat just under the skin. In very rare instances, huge overdoses of concentrated beta-carotene can cause a slight yellowing of the skin. This is not harmful and quickly goes away. It is interesting to note that the type of beta-carotene used in supplements may be harmful in large doses, especially for people who drink alcohol and smoke cigarettes.
Summary for Vitamin A
Main functions: vision, skin, mucous membranes, infection,and antioxidant.
RDA: 2333 IU for adult women and 3000 IU for adult men.
Toxicity is possible with supplemental forms of vitamin A.
Toxicity is possible with high intakes from food. No toxicity is reported for beta-carotene in food.
Tolerable upper intake level for preformed vitamin A is set at 10,000 IU daily. This may be too high for older people and pregnant women.
Deficiency is uncommon in developed countries.
Deficiency disease: night blindness and xeropthalmia.
Healthy food sources: colored fresh fruit and vegetables.
Degradation: reduced by heat, light, and oxygen.
Food Forms: provitamin A carotenoids in plants and retinyl esters in animal products.
Forms in the body: retinol, retinal, retinoic acid, retinyl palmitate, and beta-carotene.
Vitamin Ais transported through the blood bound to protein. Toxicity begins to develop when the binding proteins are all full and free retinol starts to damage cells. Children are more vulnerable to hypervitaminosis A than adults. Normally, toxicity is associated with long-term consumption of vitamin A in excess of 10 times the RDA (8,000 to 10,000 mcg/day or 25,000 to 33,000 IU/day).
People who may be susceptible to toxicity at lower doses include the elderly, pregnant women, and alcoholics. A tolerable upper intake level UL has been set at 3,000 mcg (10,000 IU)/day of preformed vitamin Afor adults and less for children. It is possible to receive excessive vitamin A from the diet. Liver is dangerously high in vitamin A. A diet consisting largely of animal products can cause hypervitaminosis A.
BETA-CAROTENE IS NON-TOXIC
No tolerable upper intake level for beta-carotene has been set because it is nontoxic. Beta-carotene is stored in fat just under the skin. In very rare instances, huge overdoses of concentrated beta-carotene can cause a slight yellowing of the skin. This is not harmful and quickly goes away. It is interesting to note that the type of beta-carotene used in supplements may be harmful in large doses, especially for people who drink alcohol and smoke cigarettes.
Summary for Vitamin A
Main functions: vision, skin, mucous membranes, infection,and antioxidant.
RDA: 2333 IU for adult women and 3000 IU for adult men.
Toxicity is possible with supplemental forms of vitamin A.
Toxicity is possible with high intakes from food. No toxicity is reported for beta-carotene in food.
Tolerable upper intake level for preformed vitamin A is set at 10,000 IU daily. This may be too high for older people and pregnant women.
Deficiency is uncommon in developed countries.
Deficiency disease: night blindness and xeropthalmia.
Healthy food sources: colored fresh fruit and vegetables.
Degradation: reduced by heat, light, and oxygen.
Food Forms: provitamin A carotenoids in plants and retinyl esters in animal products.
Forms in the body: retinol, retinal, retinoic acid, retinyl palmitate, and beta-carotene.
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