2011 February 23 by Randall Neustaedter OMD
Retinol, or vitamin A was first identified in 1907 by comparing rats fed protein and lard or olive oil for fat with rats fed a diet that added egg yolk or butterfat. The rats who ate the foods with a vitamin A deficient diet failed to grow, but recovered with the supplemental foods. Only animal fats contain vitamin A. Good sources are cod liver oil, egg yolks, butter, raw whole milk, and liver. Animals must have carotene or vitamin A sources in their diets in order to produce vitamin A and pass it on to humans. There are no plant sources of vitamin A. Betacarotene found in vegetables and fruits can be converted to vitamin A by the body in a ratio of 12:1. That is it takes 12 units of beta-carotene to produce one unit of vitamin A. Infants and people with diabetes or poor thyroid function cannot make the conversion at all. Children convert betacarotene to vitamin A very poorly. Therefore animal fat sources of vitamin A are essential for most of the population.