Vitamin A

Contrary to its name, "Vitamin A" doesn't actually refer to just a single substance; it's an umbrella term that covers a group of related chemicals. Regardless of the form of vitamin A you take, there's no disputing one simple fact: Vitamin A plays a vital role in good health.

Your Vision

You know that vitamin A is important for good eyesight but do you know why? In the eye, retinol, which is preformed vitamin A, goes through a complex chemical change which ultimately allows your eye to generate the nerve impulses that your brain interprets as "seeing". If your eye doesn't get enough of this preformed vitamin A, or retinol, the chemical process is stunted and a condition known as night blindness can develop.

Your Immune System

As important as vitamin A is to your eyesight, it's absolutely vital to your immune system. In fact, vitamin A is sometimes called the anti-infective vitamin--it's that important. Vitamin A allows your body to maintain the integrity of the cells that make up your skin and mucus membranes. These "barrier cells" are your body's first line of defense when it comes to keeping out germs and keeping those cells healthy goes a long way toward keeping you healthy.

Your Blood

When it comes to your blood, vitamin A does a couple of things. First, it allows your red blood cells to develop properly. Then, vitamin A "feeds" those blood cells by helping them get the iron they need to create hemoglobin, which carries oxygen.

Cancer Prevention

A number of different types of cancer seem to be related to vitamin A. Several animal and cell studies have linked vitamin A to a reduced risk of cancer but, unfortunately, these results haven't been repeated in real-life scenarios. What does this mean? Well, it means that, in theory, consuming appropriate amounts of vitamin A should reduce your risk of some types of cancer but the scientific proof just isn't there yet.

Vitamin A Deficiencies

Here in the U.S., we don't often hear about vitamin and mineral deficiencies but a lack of vitamin A is the leading cause of preventable blindness in Third World children.

Another very serious condition linked to vitamin A is birth defects. Though vitamin A is crucial to a developing fetus, too much or too little of this vitamin can result in birth defects of the heart, eyes and ears, especially.

Finally, we know that even children who are only slightly deficient in vitamin A have higher rates of diseases like asthma and diarrhea and are more likely to die from infectious diseases like measles. Finally, HIV-positive mothers who are deficient in vitamin A are up to 4 times more likely to pass HIV to their babies.

Natural Sources of Vitamin A

Remember your mother or grandmother giving you cod liver oil? A teaspoon of cod liver oil has many times more vitamin A than a cup of milk, a serving of spinach or even a whole sweet potato. But if you'd prefer to get your vitamin A from whole-food sources, there are a number of vegetables rich in this nutrient. Some of the best are sweet potatoes, raw carrots, cantaloup, butternut squash and eggs.

Can You Get Too Much?

It's important to remember that vitamin A is a fat-soluble vitamin. That means that your body stores any extra vitamin A that it doesn't immediately use. This also means that it's easier to over-dose on vitamin A than many people realize. To prevent vitamin A toxicity, the Linus Pauling Institute, one of the leading nutrient research institutions in the world, recommends that you avoid high-dose vitamin A supplements and stick with multi-vitamins that supply no more than 2,500 IU of vitamin A.

Excessive vitamin A intake has been associated with birth defects, osteoporosis, liver damage and other serious health conditions.

References:

National Academy of Sciences. (2001). Dietary Reference Intakes.

Linus Pauling Institute. (2003). Vitamin A