Vitamin C is the top free radical fighting vitamin.

Vitamin C (ascorbic acid is essential to survival because humans, unlike most other animals, have lost the ability to manufacture it. It is a water soluble vitamin which helps protect cells from oxidation throughout the body. One important function of vitamin C is its role in the synthesis of collagen but it plays an important role in other body functions.

Perhaps its most important role from the perspective of healthy longevity is as an effective anti-oxidant. Vitamin C can protect molecules in the body from the damage caused by free radicals which are a natural product of normal metabolism.

Regular vitamin C breaks down under oxidative stress but another form of vitamin C (ascorbyl palmitate or vitamin C ester) is fat soluble and remains effective in topical use or as a supplement longer than regular vitamin C.

The US Government recommends 90 mg per day for an adult non-smoker and 120 mg per day for a smoking adult. This dosage is sufficient to prevent diseases caused by vitamin C deficiency (scurvy) but does not reflect dosage to maintain healthy body functions. Many practitioners recommend much higher doses. There have been many studies to determine if vitamin C can reduce the seriousness or prevent other diseases and some evidence that it can be effective in some of them.

Although it is difficult to establish that high doses of vitamin C can provide significant health benefits, no studies to date have suggested that there is potential damage from high doses. The Linus Pauling Institute suggests that a tolerable upper intake of vitamin C for adults over 19 years of age is 2,000 mg per day.