Vitamin C (Ascorbic Acid)

What is vitamin C?

Vitamin C (ascorbic acid) is a water-soluble vitamin that humans — unlike most animals — cannot synthesize. It must be obtained through diet.

It is involved in numerous physiological processes:

• Collagen synthesis: cofactor for hydroxylases that cross-link collagen — essential for skin, bones, blood vessels, and wound healing
• Immune function: accumulates in white blood cells (up to 50× higher concentration than in plasma)
• Antioxidant: directly scavenges free radicals and helps regenerate vitamin E
• Iron absorption: enhances uptake of non-haem iron from plant sources

Deficiency: rare but real

True vitamin C deficiency (scurvy) is extremely rare in developed countries. But suboptimal status is more common than assumed — especially in smokers (increased turnover), older adults with limited diets, and people with very low fruit and vegetable intake.

Smokers need ~35 mg/day more than non-smokers — the recommendation rises to 135 mg/day for smokers.

The megadose myth

Linus Pauling popularized gram-dose vitamin C against colds and cancer in the 1970s. Research has not confirmed this:

• Plasma saturation occurs at ~200 mg/day
• Doses above 500 mg/day are renally excreted without proportional increase in plasma levels
• Meta-analyses show no reduction in cardiovascular disease or cancer mortality from high-dose supplementation
• Cold prevention only demonstrated under extreme physical stress

Bottom line: 200–500 mg/day from supplements or food is optimal. More is not better — and above ~2 g/day comes with risks.

What does the evidence actually show?

Clearly established (EFSA-approved)

• Collagen formation for normal function of skin, teeth, gums, bones, and cartilage
• Normal immune function
• Protection against oxidative stress
• Improved iron absorption from plant sources

Well studied

• Cold duration reduction with regular intake (~8%)
• Reduction of tiredness and fatigue (in deficiency states)

Not established

• Oral high-dose concepts in cancer contexts
• Heart attack prevention
• Anti-aging effects beyond normal requirements

Is vitamin C safe?

At 200–1,000 mg/day: likely safe. Above 2 g/day: osmotic diarrhoea possible. Above 6 g/day chronically: increased kidney stone risk (oxalate stones) in predisposed individuals. Do not combine with high-dose iron supplements and chemo- or radiotherapy without medical advice.

Food sources

Vitamin C is abundant in fresh foods: bell peppers (200 mg/100 g), rosehips (400–1,300 mg/100 g), sea buckthorn, broccoli, kiwi, citrus fruits. Anyone eating fresh fruit and vegetables daily is well supplied and does not need a supplement.