Vitamin C (Ascorbic Acid)
A water-soluble vitamin that humans lost the ability to synthesise millions of years ago (via a broken GULO gene). Required for collagen hydroxylation, catecholamine synthesis, and as a general antioxidant. Its deficiency disease — scurvy — is rare in modern diets but its role in cold-and-flu prevention and mega-dosing continues to fuel research.
Daily requirements
- Adult men: 90 mg/day.
- Adult women: 75 mg/day.
- Smokers: add 35 mg/day.
- Pregnancy / lactation: 85 / 120 mg/day.
- Tolerable Upper Intake Level: 2,000 mg/day (above this: GI upset, kidney stone risk in susceptible people).
Deficiency and scurvy
True scurvy requires vitamin C intake below ~10 mg/day for weeks to months. Early signs: fatigue, easy bruising, corkscrew hairs. Late signs: gum bleeding and tooth loss, petechiae, poor wound healing, joint pain, and if untreated, death from cardiac failure or haemorrhage. Modern cases occur in alcoholism, extreme "meat-only" diets, severe eating disorders, and institutional settings.
Cold and flu — what the evidence shows
The Hemilä Cochrane review (updated 2013, ~11,000 participants) shows regular vitamin C supplementation (200 mg+/day) does not reduce common-cold incidence in the general population. It does modestly reduce cold duration — about 8% in adults and 14% in children.
In extreme physical stress (marathon runners, soldiers on Arctic training), regular supplementation halves cold incidence. Once a cold has started, therapeutic supplementation shows no clear benefit — the effect is preventive, not curative.
High-dose IV vitamin C in cancer and sepsis
Oral vitamin C absorption saturates at ~400 mg per dose. Intravenous administration achieves much higher plasma concentrations. Randomised trials of IV vitamin C in advanced cancer (mostly single-arm or non-randomised) suggest quality-of-life improvement but not survival benefit. In septic shock, the CITRIS-ALI trial and VITAMINS trial were negative for mortality reduction. IV vitamin C remains investigational.
Food sources
- Red bell pepper (½ cup raw): 95 mg
- Orange (1 medium): 70 mg
- Kiwifruit (1 medium): 64 mg
- Broccoli (½ cup cooked): 51 mg
- Strawberries (½ cup): 49 mg
- Brussels sprouts, potatoes, tomatoes, spinach — 15–50 mg per serving
Vitamin C is easily destroyed by heat, light, and prolonged cooking. Raw or lightly cooked vegetables and fruit preserve the most.
Supplementation
- Ascorbic acid — standard, cheapest, most studied.
- Buffered forms (calcium/sodium ascorbate) — gentler on the stomach.
- Liposomal vitamin C — claims of higher bioavailability; some evidence, higher cost.
- Typical maintenance: 100–500 mg/day. High doses (> 1,000 mg/day) offer no clear extra benefit and can cause diarrhoea and kidney stones in predisposed individuals.