We've known about the properties of Vitamin A for over a hundred years even before the word 'vitamin' existed. It was originally identified in a study on how to keep cows healthy and happy, then a few years later, re-discovered as a fat-soluble nutrient in butterfat, and dubbed 'fat-soluble factor A'. By the time it was first synthesized (in 1947), the name 'vitamin A' had stuck -- even though it wasn't the first discovery in the vitamin ABCs.

Vitamin A helps fight off infections. It also helps to keep your skin smooth and supple. You can get a lot of vitamin A from your food -- with liver meats being the best source. Several vegetables -- carrots, broccoli leaves (the leaves, not the stems!), sweet potatoes and kale, run a distant second, along with butter.

Dietary vitamin A comes from two kinds of food:

• Animal food sources provide 'active' forms of vitamin A -- the body can utilize the vitamin immediately. They are called 'retinoids'. Retinoids are often used in skin creams and dermatological medicines, as vitamin A is well known for its skin rejuvenation properties.

• Plants provide carotenoids (for example beta-carotene). Carotenoids are converted by the body into vitamin A. Beta-carotene is the most common of the caroteoids. A brightly colored compound, this is what gives carrots and sweet potatoes their orange color.

'Synergy' is when two or more substances combine to create an effect greater than either could accomplish on its own. All nutrients in the body have a synergistic effect, and vitamin A is no exception. If you already have an iron deficiency that results in anemia -- not enough oxygen-transporting red blood cells that leaves you continually tired a vitamin A deficiency as well will make it worse. Iron and vitamin A supplements taken together for anemia are more effective than either of these taken singly. When you don't have enough zinc in your diet, the body has a harder time efficiently using vitamin A.

The first indication of a vitamin A deficiency is weakened vision particularly 'night blindness'the inability to see well in dim light. Vitamin A is used to form the pigments needed in the retina for vision, and without enough A, your eyes can't do their job. Remember when your mother used to tell you to eat carrots so you could see better? There's truth in that old home remedy!