Vitamin C, also known as L-ascorbic acid, this water-soluble vitamin is an antioxidant, an important player in immune function, and a building block for connective tissues and certain neurotransmitters. Unlike most animals, we humans can’t produce vitamin C on our own, so we must get it from food—or supplements.

The Evidence

There’s no question about vitamin C’s critical role in human health. Studies have shown it to decrease your odds for a whole litany of cancers: breast, lung, colon, stomach, oral, esophageal, and larynx. One study of more than 82,000 premenopausal women showed that the group with the highest daily intake of vitamin C had a 63 percent lower risk of breast cancer than the lowest-intake group. But that’s the vitamin C in food. Interestingly, large experimental studies suggest that the vitamin C you get from supplements doesn’t change your cancer risk.

What about colds, the number-one reason we reach for the vitamin C supplements? Oddly, research reviews suggest that while daily supplementation doesn’t seem to cut the risk of coming down with a cold, it can help reduce the duration of the illness. For people dealing with extreme conditions—skiers exposed to constant cold, soldiers worn down from extreme physical activity, and so forth—daily dosing with vitamin C cut the length of illness by about half. For those in more comfortable conditions, the effect was lower—a mere 8 percent less time sick. But if you don’t take your C until after symptoms occur, the effect is nil. You have to take it regularly.

“I recommend vitamin C often, and I keep a good supply level in the office at all times,” says Chris Niedzinski, D.C., owner of InnerLink Chiropractic in Wixom, Michigan. “I find that many people are deficient.”

This can lead to problems, given the vitamin’s wide-reaching activity in the body, says Dr. Niedzinski. “It’s crucial for immune function, tissue repair, limiting oxidative stress and free radical damage, building collagen, and maintaining healthy tissues, including blood vessels.” Dr. Niedzinski adds that when patients bruise easily—say, from bumping into furniture—it’s often a sign of vitamin C deficiency.

How to Use It

The vitamin C found in food reigns supreme, and you can increase your levels by eating more citrus fruits, broccoli, Brussels sprouts, and red peppers. But if you’re planning to supplement, Dr. Niedzinski recommends a dose of 1,000 milligrams per day. But scan the label before you pick your brand, he says. ”Many vitamin C products contain sugar and artificial sweeteners and colorings,” he says.

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