Vitamin C: Two Different Arguments, Often Confused

Vitamin C carries more overstatement per milligram than almost anything else on the shelf, which is unfortunate, because the well-established part is genuinely important.

What is not in doubt

• Collagen synthesis requires it. Without vitamin C the enzymes that stabilise collagen cannot work, which is what scurvy actually is — connective tissue failing
• Immune cells concentrate it, and levels fall during infection
• It regenerates vitamin E and participates in the antioxidant network
• It substantially improves absorption of non-haem iron, which is useful and occasionally a problem

The dose question

Absorption falls sharply as the dose rises. At 200 mg most is absorbed; by 1000 mg a large fraction is not, and the excess is excreted. This is the basis for the observation that most high-dose oral vitamin C produces expensive urine, and it is broadly correct.

The common-cold literature is a good example of a real but modest effect being oversold in both directions. Regular supplementation does not appear to prevent colds in the general population; it does shorten them slightly, and in people under heavy physical stress it does appear to reduce incidence. Neither finding supports the claims usually made.

The intravenous argument is a different argument

Intravenous vitamin C reaches blood concentrations that oral dosing cannot approach, and at those concentrations it behaves differently — acting as a pro-oxidant in some tissue rather than an antioxidant. That is the mechanistic basis for the interest in it as an adjunct in oncology and sepsis.

Whatever intravenous vitamin C does or does not do, it tells you nothing about a tablet. The two are not the same intervention at different sizes; they produce different concentrations and different chemistry.

The human trial results in that area remain mixed and it is not established care. Anyone considering it in the context of serious illness should be having that conversation with their oncologist rather than with a website.

A reasonable position

Food first — peppers, berries, cabbage and citrus provide plenty, and on a low-carbohydrate diet the requirement appears to fall. If supplementing, 200–500 mg daily with food captures essentially all of the benefit. Take it away from iron if iron overload is a concern, and with iron if deficiency is.