Hypervitaminosis A

Encyclopedia : H : HY : HYP : Hypervitaminosis A

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The effects of excessive vitamin A intake include:

• birth defects
• liver abnormalities,
• reduced bone mineral density that may result in osteoporosis
• hair loss
• excessive skin dryness/peeling

Signs of acute toxicity include nausea and vomiting, headache, dizziness, blurred vision, and loss of muscular coordination.

Hypervitaminosis A occurs when the maximum limit for liver stores of retinoids is exceeded. The excess enters circulation causing systemic toxicity. Vitamin A in the form of betacarotene is only selectively converted into retinoids, and hence does not cause toxicity.

Although hypervitaminosis A can occur when large amounts of liver are regularly consumed, most cases of vitamin A toxicity result from an excess intake of vitamin A in supplements. Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time.

The Institute of Medicine has established Daily Tolerable Upper Levels (UL) of intake for vitamin A from supplements that apply to healthy populations, in order to help prevent the risk of vitamin A toxicity. These levels for performed vitamin A in micrograms (µg) and International Units (IU) are:

• 0-3 years: 600 µg or 2000 IU
• 4-8 years: 900 µg or 3000 IU
• 9-13 years: 1700 µg or 5665 IU
• 14-18 years: 2800 µg or 9335 IU
• 19+ years: 3000 µg or 10,000 IU

The dose over and above the RDA is among the narrowest of the vitamins and minerals. Possible pregnancy, liver disease, high alcohol consumption, and smoking are indications for close monitoring and limitation of vitamin A administration. However, vitamin A has also been repeatedly tested and used therapeutically over several decades in larger amounts, 100,000 - 400,000 IU total dosage, for treatment of severe pediatric measles in areas where vitamin A deficiency may be present to reduce childhood mortality.

Comparative safety statistics

Deaths by vitamin poisoning appear to be quite rare in the US, typically none in a given year. However several deaths per year are typically associated with iron-containing supplements, especially brightly-colored, sugar-coated, high-potency iron supplements. This compares with 59 deaths due to aspirin poisoning in [2003], 147 deaths associated with acetaminophen-containing products in [2003], and an average of 54 deaths per year due to lightning for [1990-2003].

References

• Hussey, G.D., Klein, M. A randomized controlled trial of vitamin A in children with severe measles. NEJM, 1990, 323: 160-164.
• Ellison, J. B., Intensive Vitamin Therapy in Measles. Br Medical J, Oct 15, 1932; ii: 708-711.

See also

• Vitamin poisoning

External links

• [Facts about Vitamin A and Carotenoids], from the National Institutes of Health's Office of Dietary Supplements.

 

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