What are the Toxic Effects of Vitamin A
Excess intake of vitamin A for long duration can lead to vitamin A toxicity, unlike water-soluble vitamins, which do not have toxicity due to removal of excess water soluble vitamins through urine as they are water soluble. Vitamin A toxicity occurs when more than recommended daily allowance or RDA is taken for long time. The RDA of vitamin A for normal healthy adult is 600 mcg of retinol.
Vitamin A toxicity was first reported among Arctic explorers who ate liver of polar bear and vitamin A toxicity is also seen if it is given at very high dose of more than 150 mgs in adults and 100 mgs in children. The vitamin A toxicity is seen more commonly is Eskimos, because they eat polar bear liver and seal livers, both are very rich in vitamin A. the staple diet of Eskimo is made up of rich source of vitamin A.
Excess intake of vitamin A in the form of retinol or any other form can lead to nausea, vomiting, anorexia and sleep disturbances. These are followed by desquamation of skin, enlargement of the liver and papillar edema. Increased intracranial pressure, vertigo, diplopia, bulging fontanels in children, seizures, and exfoliative dermatitis are the common symptoms of vitamin A toxicity and in severe cases it may cause death. Other common symptoms include dry skin, cheilosis, glossitis, vomiting, alopecia, bone demineralization and pain, hypercalcemia, lymph node enlargement, hyperlipidemia, amenorrhea etc. The toxicity of vitamin A mainly occurs if excess amount of vitamin A is consumed for long time from animal sources. Excess plant vitamin A usually does not lead to severe toxicity. Excess beta carotene as found in carrots and other yellow vegetables can lead to yellow coloration of plasma and skin (called carotenemia), but this do not appear to be harmful or dangerous. But excess plant carotinoids should be avoided as it can increase chance of lung cancer in smokers. Hypothyroid patients are more susceptible to the development of carotenemia due to impaired breakdown of carotene to vitamin A. Reduction of carotenes from the diet results in the disappearance of skin yellowing and carotenemia over a period of 30–60 days in these patients.
Most recently the teratogenic (abnormality of fetus due to some compounds) effect of vitamin A is the focus of research. If excess vitamin A is given to pregnant women spontaneous abortions, craniofacial abnormalities, and valvular heart disease has been reported. Therefore, in pregnancy daily dose should not be more than 3 mg. 13-cis-retinoic acid, which is commercially available, can cause birth defects and should not be given during pregnancy and pregnancy should be avoided by contraception at least for one year after giving 13-cis-retinoic acid.
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