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Also called hypervitaminosis A, Vitamin A toxicity describes the toxic effects that occur when there is too much preformed vitamin A in the body. Vitamin A is a fat soluble vitamin that gets stored in the body in the form of retinol.
Retinol acts as a storage form of vitamin A, which can be converted to and from retinal, the active aldehyde form of the molecule. One of the richest animal sources of Vitamin A is liver. Any vitamin A that is not required immediately is stored for future use in bodily functions, meaning vitamin A deficiency is rare in individuals who maintain a healthy, balanced diet.
Hypervitaminosis A may be acute or chronic. The acute form of the condition occurs as a result of ingesting large amount of vitamin A over a short period, such as few hours or days, whereas the chronic form results when the vitamin accumulates in the body gradually over a long period. The excess vitamin A may have been ingested via the diet, vitamin supplementation or the use of prescribed medicines.
Examples of the symptoms observed for acute and chronic forms of the condition are described below, although headache, rash, nausea and vomiting are common to both forms.
Acute hypervitaminosis A
Chronic hypervitaminosis A
An excess intake of vitamin A during pregnancy can increase the risk of fetal abnormalities developing. According to the World Health Organization, the daily intake during any period of pregnancy should not be more than 3000μg and the weekly intake should never exceed 7500μg.
According to the National Institutes of Health, the recommended daily intakes of vitamin A among different age groups are: