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Supplements BODY HANDBOOK
Supplements · §560
Vitamin C
Vitamin C is one of the few nutrients your body can't make and can't store, so you need a little every day, forever. But the number that matters is smaller than the bottle wants: about 200 mg a day fills your tissues, and one large orange gets you halfway. Past that point the pills mostly become expensive urine, and the biggest promise on the label, that it fends off colds, is largely false. The real wins are cheaper and quieter than the marketing.
Do · Daily Evidence Moderate Chapter Supplements

What it actually does. Your body can't build collagen, the rope holding skin, gums, blood vessels and bones together, without vitamin C: the enzyme that assembles it stalls after each step, and vitamin C resets it 1. Run out completely and the collagen falls apart, which is scurvy. It also pries plant iron loose in the gut so you can absorb it 2.

The dose has a hard ceiling. Blood levels plateau at about 200 mg; past 500 mg at once, less gets absorbed and the surplus is gone in hours 3. That saturating dose, not the lower deficiency floor, is what reasonable people have argued for since the 1990s 4.

The colds claim is mostly wrong. A daily habit does not stop the average person catching colds; it only shortens them by about 8% in adults 5. The lone exception: people pushing to the limit, like marathoners and soldiers on subarctic exercises, roughly halve their cold risk.

The longevity link is the diet, not the pill. People with the highest blood vitamin C die at about half the rate of those with the lowest 6 7, yet tablets in trials produced no such benefit. High blood levels just tag a fruit-and-vegetable life; the pill isn't what's working.

The whole routine is one habit.

How much you notice depends on where you start. If you were running low, the change is fast: within a few weeks, gums that bled at every brushing stop streaking the brush red, cuts close on schedule, bruises fade in days 9.

Over one to three months, if you've paired it with iron-rich meals, low iron lifts and stairs stop leaving you breathless 2. If you already eat two or three produce servings a day, a pill on top is invisible; you're past the ceiling.

The fine print — when to skip it, and what people get wrong

"Megadoses treat cancer": 10 g/day oral beat placebo in zero of three trials 11. "Liposomal is 5-10x more absorbable": not at matched doses. "Food can't get you enough": one orange is half a day 3.

References
  1. 1Institute of Medicine (2000). Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. link
  2. 2Hallberg L (1987). Is there a physiological role of vitamin C in iron absorption? Annals of the New York Academy of Sciences. link
  3. 3Levine M, Conry-Cantilena C, Wang Y et al. (1996). Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proceedings of the National Academy of Sciences. link
  4. 4Carr AC, Frei B (1999). Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. American Journal of Clinical Nutrition. link
  5. 5Hemilä H, Chalker E (2013). Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews. link
  6. 6Khaw KT, Bingham S, Welch A et al. (2001). Relation between plasma ascorbic acid and mortality in men and women in EPIC-Norfolk prospective study. The Lancet. link
  7. 7Aune D, Keum N, Giovannucci E et al. (2018). Dietary and circulating vitamin C, vitamin E, β-carotene and risk of total cardiovascular mortality: a systematic review and dose–response meta-analysis of prospective observational studies. Public Health Nutrition. link
  8. 8Schectman G, Byrd JC, Gruchow HW (1989). The influence of smoking on vitamin C status in adults. American Journal of Public Health. link
  9. 9Tada A, Miura H (2024). Does vitamin C supplementation provide a protective effect in periodontal health? A systematic review and meta-analysis. International Journal of Molecular Sciences. link
  10. 10Thomas LDK, Elinder CG, Tiselius HG, Wolk A, Åkesson A (2013). Ascorbic acid supplements and kidney stone incidence among men: a prospective study. JAMA Internal Medicine. link
  11. 11Moertel CG, Fleming TR, Creagan ET et al. (1985). High-dose vitamin C versus placebo in the treatment of patients with advanced cancer who have had no prior chemotherapy. New England Journal of Medicine. link
Related in the handbook (8)
Works well with
  • — Vitamin C with a meal pulls two to three times more iron out of plant foods; pair them on purpose.
Related
  • — Collagen synthesis needs vitamin C as a cofactor; the peptides do nothing without it on board.
  • — An adjacent topic in the handbook.
  • — Eating vitamin C with a plant-based meal counters phytic acid, pulling more of the bound iron into your blood.
  • — Cooking veg can wipe out their vitamin C. Eat some raw, or cook only briefly, to keep what's there.
  • — Topical vitamin C is one of the skincare actives worth using — the same collagen-supporting nutrient, applied where you want the effect.
  • — Bleeding gums aren't always plaque; a vitamin-C shortfall is a quieter cause worth ruling out.
  • — An adjacent topic in the handbook.
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