Adipose tissue, carotene vitamin

P-Carotene (provitamin A) is one of several naturally occurring precursors of vitamin A. Owing to inefficient intestinal conversion, only one-sixth of the dietary intake of 3-carotene is ultimately converted to retinol (Goodman, 1979). Additionally, as the amount of 3-carotene in the diet increases, the conversion to retinol decreases so that systemic vitamin A toxicity is not caused even by massive doses. A variable amount of 3-carotene is also absorbed unchanged from the intestine, enters into circulation, and is stored in adipose tissue. 

Carotenoids are frequently added as colorants to processed foods such as margarines, and when in the form of P-carotene can contribute substantially to the vitamin A activity of diets (Klaui and Bauemfeind, 1981). Some carotenoids may be obtained from animal food products such as egg yolk, milk, and butter, and a small amount from animal tissues where they are deposited mostly in adipose fat. These carotenoids are derived from those animal species that absorb carotenoids and that have yellow fat. However, not all carotenoids that are deposited in animal tissue or those found in the circulation have provitamin A activity. This varies considerably among species and is related first, to their ability to absorb various individual forms of carotenoids, and second, to the chemical alterations that may occur subsequent to absorption. 

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