Vitamin A is an important fat-soluble vitamin. Its basic molecule is a retinol, or vitamin A alcohol. In Western countries, 70% of dietary vitamin A is preformed as all trans-retinol. After absorption, retinol is transported via chylomicrons to the liver, where it is either stored as retinol ester or re-exported into the plasma in combination with retinol-binding protein for delivery to tissue sites.
Sources of vitamin A include external supplementation and synthesis within the body from plant carotenes. The best sources of preformed vitamin A are liver, milk, kidney, and fish oil. The carotene substrates necessary for the synthesis of vitamin A are mainly found in plants, principally carrots.
The bioavailability of retinol generally is more than 80%, whereas the bioavailability and bioconversion of carotenes are lower. These may be affected by species, molecular linkage, amount of carotene, nutrition status, genetic factors, and other interactions.
While in general the body absorbs retinoids and vitamin A very efficiently, it lacks the mechanisms to destroy excessive loads. Thus, the chances for toxicity exist unless intake is regulated carefully. Revision of earlier estimates of daily human requirements of vitamin A has been suggested; the suggestion is that estimates ought to be revised downwards. Concern exists about the teratogenicity of vitamin A.
Pathophysiology
The recommended daily allowance for vitamin A is 5000 international units (IU) for adults and 8000 IU for pregnant or lactating women.
Being fat-soluble, vitamin A is stored to a variable degree in the body, making it more likely to cause toxicity when taken in excess amounts. In contrast, water-soluble vitamins generally are excreted in the urine and stored only to a limited extent; hence, adverse effects only occur when extremely large amounts are taken.
http://www.emedicine.com/med/topic2382.htm
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ETA: Most pure vitamins have little to know serious toxicity. Iron is one that does and has deaths linked to it.
But err on the side of caution, its usually best to limit most fat soluable vitamins within their RDA.