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From the research that I have done, I know that antioxidants such as vitamin c donate electrons to oxygen free radicals and effectively neutralize them. They themselves do not become free radicals as they are stable in both forms.

So, would it be correct to say that after the vitamin C is oxidized(giving electrons to free radicals) so much that it can no longer give any more electrons(not sure what the actual limit is):

  1. What happens to vitamin C (does it get broken down and therefore decrease)
  2. Is it any useful in destroying free radicals?
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Correct, vitamin C (ascorbate) acts by donating 1 electron to a free radical (reducing them to a stable compound with paired electrons), and is thereby itself oxidized to semidehydroascorbate. This is actually a radical itself, but can be reduced back to ascorbate by thioredoxin reductase or cytochromes, using NADH or NADPH as the reducing agent. A pathway diagram with references is found here.

So to answer (1), ascorbate is continuously recycled after neutralizing free radicals, and is therefore not consumed to any large extent. Therefore, vitamin C is only needed in the diet to replenish the small fraction that is lost from the body (about 1--3% per day; see this book).

And yes, vitamin C is very important in defense against free radicals; it is considered the major water-soluble antioxidant in humans.

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