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Vitamin A is a generic term for a group of compounds that are obtained by conversion from carotenoids in the liver, its storage organ. Retinol and retinal (aldehyde) are often referred to as preformed vitamin A. While green and yellow vegetables contain carotenoids, retinol is concentrated in egg yolks and the livers of many animals. Whether taken from dietary sources or synthesised by your liver, Vitamin A is essential for growth and reproduction, for maintaining healthy vision and for supporting protein synthesis and cell differentiation.
Vitamin A and its analogues seem to help to maintain proper DNA function. That is in contrast with the results of a study, according to which too much beta-carotene for individuals with specific lifestyles (smokers, etc.,) without other carotenoids and antioxidants, may be harmful.
Beta-carotene is the most potent precursor to vitamin A, but its conversion to vitamin A in the body is limited. It remains an important antioxidant in its own right and only in rare circumstances can build up to toxic levels. Beta-carotene helps to support immune health by enhancing the function of the thymus gland.