Gleaned from the internet:

The carotenoid family includes alpha and beta-carotene, lutein, zeaxanthin, cryptoxanthin and lycopene. Vitamin A is actually a family of substances called retinoids that includes retinol, retinal, and retinoic acid. These are called preformed vitamin A because they are in a form that your body readily uses.

The body must convert three of these compounds—beta-carotene, alpha-carotene, and beta-cryptoxanthin—to vitamin A. But in humans, this conversion is quite inefficient, with about 10 to 20 molecules of carotenoids needed to make one of vitamin A. In addition, 80 percent or more of natural vitamin A from animal sources.

Also, here is an article we feature on our site that you might find interesting:

The Bell Shaped Curve

Remarkable British Medical Journal Paper shows Vitamin A Limits Vitamin D Cancer Benefits

by John Cannell, MD

(The Vitamin D Council) A few weeks ago, the British Medical Journal published a remarkable paper, remarkable that it studied more than 500,000 subjects, remarkable that it had 56 (fifty-six) authors, remarkable that it confirmed low vitamin D levels obtained in the past are a risk factor for developing colon cancer in the future. However, the most remarkable part of the paper is that the 46 scientists minimized the true significance of their own research. They found that vitamin A, even in relatively low amounts, appears to thwart vitamin D's association with reduced rates of colon cancer.

Read More:

http://www.tbyil.com/Bell_Shaped_Curve.htm

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As Luella says, we take and love the supreme all-around nutritional supplement IntraMAX. It contains a whopping 415 different organic, whole-food derived nutrients in optimal amounts and the body utilizes every single one of them! Compare that to the measly handful of vitamins and minerals and their typically puny amount recommendations on the RDA list. No trace mineral, no enzymes, no other phyto-nutrients . . .

The fact is, it is literally impossible to get even the puny recommended RDA vitamins and minerals every day from food alone on a typical 2000 to 2500 calorie diet- not with our mineral depleted soils and packaged foods on the grocers' shelves which have had the nutrients processed out and harmful additives processed in for color, taste, texture, shelf-live and cost-savings - and then often enriched with coal-tar derived petrochemical pseudo vitamins and crushed rock minerals. Those enriched items are poorly absorbed and not the same as what is found in nature. Our natural bodies know the difference and may identify the fake vitamins as toxins, which are the number one cause of disease and illness, including cancer.

OK, off my soapbox.

: )