Chronic hypervitaminosis A

Vitamin A toxicity is relatively rare. Hypervitaminosis A is caused by excessive intake of preformed vitamin A.

The risk of developing hypervitaminosis A is derived from total cumulative vitamin A intake rather than a specifically daily usage level.

Chronic hypervitaminosis A results from continued ingestion of high doses. Chronic hypervitaminosis A is more common than acute hypervitaminosis A.

Serum levels of vitamin A are generally less than 3.49 umol/ liter and there are increased levels of the unbound retinol resulting in a change in the ratio of free retinol to retinol bound to RBP as well as increase in retinyl esters.

Symptoms of hypervitaminosis A include dryness of the skin, headache, anorexia, bone fragility, weakness, hair loss, malaise, itching joint pain, vertigo, vomiting, irritability, and in babies, a bulging fontanelle and increased intracranial pressure.

It may also cause emotional lability and hepatosplenomegaly.   Epimetaphyseal abnormalities may be observed in chronic hypervitaminosis A, including invagination of the epiphysis into the metaphysis and thinning of the physeal plate.

Chronic hypervitaminosis A usually develops after doses of more than 100,000 IU/day have been taken for months.
Chronic hypervitaminosis A

Notes
*RBP – retinol binding protein