They are stored in the liver and adipose tissue. McCollum and Davis found that rats raised on a fat-free diet weren't healthy and ether extract of eggs or butter will cure the problem. Vitamin A was discovered by Mori in 1922 as a fat soluble factor. Retinol is the chemical name of vitamin A. Retinal and retinoic acid are related compounds. The former requires retinal and the latter requires retinoic acid.
Some animals can absorb beta-carotene and process it in the liver.
Vitamin A activity depends on its double bonds which are quite labile. Antioxidant is required to protect vitamin A. Night blindness, dryness of eyes, diarrhea, kidney stones and abortion are some typical vitamin A deficiency symptoms. A intake will eventually lead to toxicity. Symptoms include dermatitis, skin thickening and weight loss. Each international unit represents 0.3 g retinol.