An extract:-Vitamin A: This all-important vitamin is a catalyst on which innumerable biochemical processes depend. According to Dr. Price, neither protein, minerals nor water-soluble vitamins can be utilized by the body without vitamin A from animal sources.6 Vitamin A also acts as an antioxidant, protecting the body against pollutants and free radicals, hence against cancer. Vitamin A stimulates the secretion of gastric juices needed for protein digestion, plays a vital role in building strong bones and rich blood, contributes to the production of RNA and is needed for the formation of visual purple. Sources of preformed vitamin A (called retinol) include butterfat, egg yolks, liver and other organ meats, seafood and fish liver oils. Provitamin A or carotene is also a powerful antioxidant. It is found in all yellow, red, orange or dark green fruits and vegetables. Carotenes are converted to vitamin A in the upper intestine. Vegetarians claim that the body’s requirements for vitamin A can be met with carotenes from vegetable sources, but many people–particularly infants, children, diabetics and individuals with poor thyroid function–cannot make this conversion.7 Furthermore, studies have shown that our bodies cannot convert carotenes into vitamin A without the presence of fat in the diet.8 Dr. Price discovered that the diets of healthy isolated peoples contained at least ten times more vitamin A from animal sources than found in the American diet of his day. The high vitamin A content of their diets insured them excellent bone structure, wide handsome faces with plenty of room for the teeth and ample protection against stress of all types. It is best to obtain vitamin A from natural sources like yellow butter, egg yolks, organ meats, fish, shellfish and cod liver oil as high amounts of synthetic vitamin A from supplements can be toxic, especially to those with impaired liver function and to those whose diets are otherwise poor. High levels of natural vitamin A have no toxic effects, in spite of the medical establishment’s dire warnings to the contrary. Antibiotics, laxatives, fat substitutes and cholesterol-lowering drugs interfere with vitamin-A absorption. - See more at: westonaprice.org/health-top...
Interesting bit about poor thyroid function and the conversion of carotenes from vegetable sources.