The dangers and benefits of vitamin C...

Ever since Linus Pauling advocated large doses as a cure for the common cold, the benefits of vitamin C have always been a controversial subject. Many of the claims Pauling made about vitamin C attracted attention because he won the coveted Nobel Prize in both chemistry and peace.

You'll often see vitamin C called ascorbic acid, a term that literally means "no scurvy". Some 250 years ago, a British physician found that sailors given citrus fruits were cured of scurvy (which is the result of a vitamin C deficiency).

Unfortunately, the British Navy waited 50 years until they acted on this information and required all its vessels to provide lime juice to every sailor. The term limey was given to British sailors because of this requirement.

Dehydroascorbic acid and ascorbic acid are the active forms of vitamin C found in food. Most supplements contain only ascorbic acid. Levels of ascorbic acid in the blood rise to the same degree following the consumption of both vitamin C containing foods and ascorbic acid.

Because of this, some have concluded that supplements offer the same benefit as food. However, this ignores the fact that dehydroascorbic acid (the other active form of vitamin C) may have positive effects other than that of raising ascorbic acid levels [19]. In fact, your body can absorb and use both forms of vitamin C [29].

One of the main benefits of vitamin C is its function as an antioxidant.

If you leave an iron nail outside, it will rust. Slice an apple in half, and it turns brown. Both are examples of oxidation, defined as a chemical reaction that involves the loss of an electron from an atom. Dip a sliced apple in lemon juice, however, and the rate at which the apple turns brown is slowed. That's because the vitamin C in the lemon juice slows the rate of oxidative damage.

Free radicals are molecules with an unpaired electron. In this state, they're highly reactive and destructive to everything that gets in their way.

Although free radicals have been implicated in many diseases, including heart disease and cancer, they're actually a normal part of your body chemistry, and can help to keep you healthy. White blood cells, for example, use free radicals to "attack" viruses and bacteria.

Optimal health, however, requires a balance between free radical generation and antioxidant protection. One of the functions of an antioxidant is to "quench" these free radicals before they create too much damage.

However, there is research to show that vitamin C may act as a pro-oxidant [15]. In other words, vitamin C, under certain conditions anyway, may act in a manner that is opposite to its intended purpose. This has raised concern among thousands of people who supplement their diets with vitamin C because of its antioxidant benefits.

So, is vitamin C all it's cracked up to be? Does it really offer all the health benefits most of us believe in?

Vitamin C and other antioxidants are often recommended on the basis that they improve athletic performance.

And it's true that...