Vitamin C is one of the most supplemented nutrients, yet most people who take it probably don't need it. The evidence for high-dose vitamin C is far weaker than marketing claims suggest.
Here's what actually matters: the RDA (recommended dietary allowance), whether you're deficient, and whether supplementation produces real benefits.
What Vitamin C Does
Vitamin C (ascorbic acid) is a water-soluble vitamin involved in several critical functions:
Antioxidant activity: Vitamin C neutralises free radicals, protecting cells from oxidative stress. This is why it's marketed for immune health.
Collagen synthesis: Vitamin C is a cofactor for enzymes that stabilise and cross-link collagen. Without adequate vitamin C, your body can't properly form collagen (skin, tendons, ligaments, bone matrix).
Immune function: Vitamin C supports immune cell function and antibody production. It's involved in fighting infections.
Iron absorption: Vitamin C enhances non-haem iron (plant-based iron) absorption, which is why it's often paired with iron supplements.
All of these are real and important. The question is whether you need supplementation beyond food sources.
RDA and Who's Actually Deficient
RDA (Recommended Dietary Allowance):
- Adult men: 90mg daily
- Adult women: 75mg daily
- Smokers: add 35mg to the above
These are set to prevent deficiency (scurvy), not to optimise health. 90mg is a low threshold.
Food sources (easily achievable):
- 1 orange: ~85mg
- 1 cup strawberries: ~90mg
- 1 cup broccoli: ~100mg
- 1 red bell pepper: ~150mg
Someone eating 1 orange and a few servings of vegetables reaches the RDA trivially.
Who's genuinely deficient?
- Smokers (vitamin C is metabolised faster)
- People with malabsorption issues (Crohn's, celiac disease)
- People eating only processed foods
- Extremely restrictive diets
For anyone eating a reasonable diet with basic fruit and vegetables, deficiency is unlikely.
The High-Dose Vitamin C Debate
Linus Pauling (Nobel Prize winner) famously promoted megadoses of vitamin C for colds and general health, claiming massive benefits.
The research since then: Modest.
High-dose vitamin C for preventing colds: meta-analyses show minimal benefit in healthy people. Taking 1-2g daily doesn't prevent colds. It might reduce cold duration by 8-12 hours in some populations, but the effect is small.
High-dose vitamin C for athletic performance: some evidence that vitamin C reduces muscle soreness (DOMS) and supports recovery, but the effects are modest.
High-dose vitamin C for antioxidant benefits: here's where it gets complicated. While vitamin C is an antioxidant, taking megadoses might actually impair training adaptations. More on this below.
Realistic take: High-dose vitamin C (1-2g+) produces modest benefits at best in healthy people. It doesn't prevent colds, it doesn't dramatically improve immune function, and it doesn't cure disease.
The Antioxidant Paradox with Training
This is important for lifters specifically.
Research by Ristow and others (2009) showed that high-dose antioxidant supplementation (including vitamin C) blunted hormetic training adaptations — the positive cellular stress responses that drive fitness improvements.
The mechanism: exercise induces mild oxidative stress, which triggers adaptive responses (mitochondrial biogenesis, increased antioxidant production, improved insulin sensitivity). If you immediately quench that oxidative stress with megadoses of antioxidants, you suppress the adaptation.
Practical upshot: taking 1-2g of vitamin C post-workout might blunt some training adaptations. Better to let the training stimulus fully activate before flooding yourself with antioxidants.
This is particularly relevant for endurance and aerobic training adaptations.
Vitamin C and Collagen Synthesis
This is where vitamin C supplementation has legitimate evidence.
Collagen synthesis requires vitamin C as a cofactor. Adequate vitamin C is necessary for proper collagen formation (skin, tendons, ligaments, bone).
Studies on collagen supplementation often include 500-1000mg vitamin C because the vitamin C enhances collagen synthesis from the supplemental collagen peptides.
The protocol: 10-15g collagen peptides + 500mg vitamin C, taken with carbs and protein, pre-exercise (or post-exercise). This combination supports connective tissue health.
For healthy people eating adequate vitamin C, this is unnecessary. But for people taking collagen supplements specifically for joint health or skin health, adding vitamin C makes sense.
Dosing: How Much Do You Actually Need?
To prevent deficiency: 90mg daily (easily achieved through food)
For potential immune support: 200-500mg daily (no additional benefit above this)
For collagen synthesis: 500mg daily with collagen peptides
For potential recovery enhancement: 500-1000mg daily, but beware the antioxidant paradox if you're endurance training
Megadose range: 1000mg+ daily. Minimal additional benefits, risk of GI upset and potential interference with training adaptations.
Practical Recommendation by Scenario
Eat adequate fruits and vegetables? No supplementation needed. You get enough from food.
Eat poorly, rarely have fruit? Take 200mg daily supplement. Ensures you're not deficient.
Take collagen supplements? Add 500mg vitamin C daily with the collagen. Improves synthesis.
Want to hedge your bets for immune health? 200-500mg daily. Won't prevent colds, but ensures adequate levels.
Competitive athlete wanting training adaptations maximised? Avoid high-dose vitamin C post-workout. Let training stress fully activate. Food sources only.
Smoker? Add 200mg daily to the standard RDA (total ~300mg).
Malabsorption issue? Consult your doctor. Supplementation is justified, but amounts depend on your situation.
Cost vs Benefit
Vitamin C supplements are cheap (£0.05-0.30 per day depending on dose).
The benefit-to-cost ratio is excellent if you need it (deficient or poor diet), and non-existent if you're already adequate (normal diet).
Most people taking vitamin C are in the latter category — they don't need it but take it for "insurance."
That's not irrational (it's cheap insurance), but it's not necessary.
Bottom Line Recommendation
Do you eat at least 1 fruit and several servings of vegetables daily?
If yes: you don't need vitamin C supplementation. You're getting enough from food. Save your money.
If no: take 200mg daily to cover your bases. Ensures you're not deficient.
Taking collagen supplements for joint or skin health?
Add 500mg vitamin C daily with the collagen. This is the one scenario where supplementation has solid evidence of benefit.
Megadose vitamin C (1g+)?
Skip it. It won't prevent colds, won't significantly improve immunity in healthy people, and might blunt training adaptations. Food sources are adequate.
Scurvy risk (extremely restrictive diet)?
Get actual medical evaluation. Vitamin C supplementation is justified, but you probably have other nutrition issues too.
The Honest Take
Vitamin C is essential. Deficiency is real (historically). But modern deficiency is rare in developed countries.
Supplementation beyond food sources is unnecessary for most people. High-dose vitamin C is overhyped and produces minimal additional benefit.
Taking a standard multivitamin with 60-100mg vitamin C? Fine, harmless. Taking megadose vitamin C daily? Probably wasteful. Ensuring adequate vitamin C through food? Optimal.
The money saved from not supplementing vitamin C is better spent on food quality, training consistency, and sleep.