Hypervitaminosis A
2941264
221338918
2008-06-24T02:28:30Z
Arcadian
104523
/* Presentation */ ref
{{DiseaseDisorder infobox |
Name = Hypervitaminosis A |
Image = Retinol structure.svg |
Width = 350 |
Caption = |
ICD10 = {{ICD10|E|67|0|e|65}} |
ICD9 = {{ICD9|278.2}} |
ICDO = |
OMIM = |
DiseasesDB = 13888 |
MedlinePlus = |
eMedicineSubj = med |
eMedicineTopic = 2382 |
}}
'''Hypervitaminosis A''' refers to the effects of excessive [[vitamin A]] (specifically retinoid) intake.
==Presentation==
Effects include:
* [[birth defect]]s
* [[liver]] problems,
* reduced [[bone mineral density]] that may result in [[osteoporosis]]
* coarse bone growths
* skin discoloration
* [[hair loss]]
* excessive skin dryness/peeling ([[desquamation]])
* [[idiopathic intracranial hypertension]]<ref name="pmid18460275">{{cite journal |author=Wall M |title=Idiopathic intracranial hypertension (pseudotumor cerebri) |journal=Curr Neurol Neurosci Rep |volume=8 |issue=2 |pages=87–93 |year=2008 |month=March |pmid=18460275 |doi= |url=}}</ref>
==Signs==
Signs of acute toxicity include [[nausea]] and [[vomiting]], [[headache]], [[dizziness]], blurred [[Visual perception|vision]], and loss of [[muscle|muscular]] coordination.
==Pathophysiology==
Hypervitaminosis A occurs when the maximum limit for liver stores of retinoids is exceeded. The excess vitamin A enters the 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 the form of vitamin supplements. Toxic symptoms can also arise after consuming very large amounts of preformed vitamin A over a short period of time. (See Polar-bear liver below.)
Vitamin A causes cells to swell with fluid, too much vitamin A causes them to rupture in hypoosmotic environments, hence the toxicity. Toxicity has been shown to be mitigated through vitamin E, Cholesterol, Zinc, Taurine and Calcium.
==Recommended supplement limits==
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 preformed vitamin A in [[microgram]]s (µg) and [[International Unit]]s (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 [[Dietary Reference Intake|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, in order to reduce childhood mortality.<ref name="Hussey1990">{{cite journal |author=Hussey GD, Klein M |title=A randomized controlled trial of vitamin A in children with severe measles |journal=NEJM |volume=323 |pages=160–164 |year=1990}}</ref><ref name="Ellison1932">{{cite journal |author=Ellison JB |title=Intensive vitamin therapy in measles |journal=Br Medical J |volume=ii |pages=708–711 |year=1932}}</ref>
==Toxicity from eating liver==
The [[liver]] of certain animals — including the [[polar bear]], [[Pinniped|seal]], and [[sled dog|husky]] — is unsafe to eat because it is extraordinarily high in [[vitamin A]]. This danger has long been known to the [[Inuit]] and has been recognized by Europeans since at least 1597 when [[Gerrit de Veer]] wrote in his diary that, while taking refuge in the winter in [[Novaya_Zemlya|Nova Zembla]], he and his men became gravely ill after eating polar-bear liver.<ref name="lips2003">{{cite journal | title=Hypervitaminosis A and fractures | author=Paul Lips | journal=N Engl J Med | volume=348 | pages=1927–1928 | date=2003-05-08 | url=http://content.nejm.org/cgi/content/short/348/4/347 | accessdate=2008-03-06 | pmid=12540650 | doi=10.1056/NEJMe020167}}</ref> In [[1913]], [[Antarctica|Antarctic]] explorers [[Douglas Mawson]] and [[Xavier Mertz]] were both poisoned, the latter fatally, from eating the liver of their [[sled dog]]s.<ref>[http://student.bmj.com/issues/02/05/life/158.php Student BMJ Man's best friend?]</ref>
[[Vitamin A]] itself was not discovered until [[1917]].
The livers of many other animals have lower levels of vitamin A and [[Liver#Liver as food|are commonly eaten]].
==References==
<references/>
==See also==
*[[Vitamin poisoning]]
*[[Xavier Mertz]] (first documented death of Hypervitaminosis A after consuming a sled dog's liver during an Antarctic expedition)
==External links==
*[http://ods.od.nih.gov/factsheets/cc/vita.html#risk Facts about Vitamin A and Carotenoids], from the [[National Institutes of Health]]'s Office of Dietary Supplements.
{{Nutritional pathology}}
[[Category:Toxicology]]
[[fr:Hypervitaminose A]]
[[pt:Hipervitaminose A]]