Toxicity

Cumulative toxicity is possible when doses greater than 100 000 IU are ingested long term. Acute toxicity is very difficult to induce in adults, as doses above 2 000 000 IU are required (Hendler et al 2001).

Early signs of toxicity include dry rough skin, cracked lips, coarse hair, sparse hair, alopecia of eyebrows, diplopia, dryness of the mucous membranes, desquamation, bone and joint pain, fatigue and malaise, nausea and vomiting, and psychological changes mimicking depression and schizophrenia.

Later signs include irritability, increased intracranial pressure and headache, dizziness, liver cirrhosis, fibrosis and cirrhosis, vomiting, haemorrhage and coma (Miller etal 1998).

People with chronic renal disease typically have elevated plasma retinol levels and therefore may be at greater risk of toxicity if supplementation is used.

It is important to note that beta-carotene is not associated with teratogenic effects or vitamin A toxicity and is considered a far safer nutrient.

Clinical note — Vitamin A toxicity in two young children

In 2001, a report of two children admitted to hospital with symptoms of vitamin A toxicity was published in the Medical Journal of Australia. One case involved a 2-year-old girl with anorexia, lethargy and leg pain, an erythematous rash over her back and elbows and irritability. All symptoms resolved over 2 weeks following withdrawal of the supplement. The second case involved a child who had previously been prescribed oral etretinate by a dermatologist (for an unspecified period of time), which was ceased 3 months prior to vitamin A supplementation. In both cases, the dose of vitamin A taken was in excess of that provided by standard OTC products (Coghlan & Cranswick 2001).

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