Vitamin C is one of those nutrients athletes hear about constantly — usually paired with promises that it will “boost” immunity and keep you training through winter. The reality is more nuanced, and more interesting. The honest headline: vitamin C contributes to the normal function of the immune system, and for people doing regular intense exercise there’s a specific, EU-authorised claim worth knowing about. But it does not prevent colds — and being clear about that distinction is the whole point of this guide.
What vitamin C actually does in the body
Vitamin C (ascorbic acid) is a water-soluble vitamin, which means your body can’t store it — excess is excreted rather than stockpiled, so a regular intake from food or supplements matters. The EU Nutrient Reference Value (NRV) is 80 mg per day, and the NHS puts the UK recommended intake at around 40 mg.
Its authorised roles are broad and genuinely relevant to anyone who trains:
- Immune function: vitamin C contributes to the normal function of the immune system.
- Collagen formation: vitamin C contributes to normal collagen formation for the normal function of bones, cartilage, gums, skin and blood vessels — the connective tissue that takes a beating in any sport.
- Oxidative stress: vitamin C contributes to the protection of cells from oxidative stress. Exercise generates free radicals; antioxidants like vitamin C are part of the body’s normal response.
- Energy metabolism: vitamin C contributes to normal energy-yielding metabolism.
- Tiredness and fatigue: vitamin C contributes to the reduction of tiredness and fatigue.
- Iron absorption: vitamin C increases iron absorption from plant-based foods — useful if your diet is mostly plant-based and iron is a concern.
The athlete-specific immune claim (and its condition)
Here’s where it gets genuinely athlete-relevant. There’s one EU-authorised claim that goes a step further than the general immune statement:
Vitamin C contributes to maintaining the normal function of the immune system during and after intense physical exercise.
The important detail: this claim is only authorised when the daily intake is 200 mg in addition to the normal recommended intake. So if you’re logging hard sessions regularly, making sure you’re comfortably above the baseline NRV is a reasonable goal — not as a magic shield, but as basic nutritional housekeeping.
Does vitamin C prevent colds? The honest answer
This is the question most people actually want answered, so let’s be direct.
Large systematic reviews, including the well-known Cochrane analysis, consistently find that routine vitamin C supplementation does not prevent colds in the general population. Across thousands of participants, regular supplementation did not reduce how often people caught colds.
It may modestly shorten duration — on the order of 8% in adults, which is roughly a day off a typical cold — and there’s evidence of a benefit for people exposed to severe short-term physical stress, such as marathon runners or skiers training in the cold. That’s a specific context, not a general promise.
The takeaway: vitamin C is not a cold-prevention supplement. What it is, is an essential nutrient with well-established roles in immune function, collagen synthesis and antioxidant defence — roles that matter more when you’re training hard and placing real demands on your body.
Getting enough: food first
The good news is that vitamin C is genuinely easy to get from a normal diet. Rich sources include:
- Red and yellow peppers (among the highest sources per gram)
- Kiwi fruit
- Citrus fruits — oranges, grapefruit, lemons
- Berries — strawberries, blackcurrants
- Broccoli and Brussels sprouts
- Tomatoes
A single kiwi or a serving of red peppers takes you past the NRV. If your diet includes a reasonable variety of vegetables and fruit, deficiency is unlikely. Supplementing makes most sense when diet quality is poor, during high training loads, or if you’re targeting that athlete-specific 200 mg extra intake.
What about high doses?
Because vitamin C is water-soluble, excess is excreted rather than accumulated in tissues — megadosing doesn’t bring megabenefits. Very high doses (typically above 1,000 mg per day) can cause digestive discomfort, diarrhoea and stomach cramps. There’s no authorised claim for any performance-enhancing effect of high-dose vitamin C, and the evidence doesn’t support one. More is not better here.
Where vitamin C fits in your routine
CapyFuel’s range focuses on performance-first supplements — whey, creatine, pre-workout, BCAAs — because those have the strongest evidence for training outcomes. Vitamin C sits in a different category: a foundation micronutrient best covered through diet, with supplementation as a safety net during heavy training periods.
If you’re thinking about immune support and recovery more broadly, it’s worth seeing how vitamin C works alongside other micronutrients. Zinc and vitamin D are similarly cited for immune function; magnesium plays a role in muscle function and energy metabolism; and electrolyte balance underpins performance in the first place.
The bottom line: eat your peppers, keep your diet varied, and if you’re training hard through winter, a modest vitamin C top-up to hit that 200 mg-above-NRV threshold is a sensible, evidence-grounded habit — just not a cold-proof one.
Related: Vitamin D for athletes · Zinc for athletes · Magnesium for athletes · Electrolytes & hydration.
Frequently asked questions
Does vitamin C prevent colds?
No — and this is worth being clear about. Large systematic reviews, including the Cochrane analysis, consistently find that routine vitamin C supplementation does not prevent colds in the general population. It may modestly shorten duration, and there is specific evidence for people under severe physical stress (endurance athletes, cold-environment training), but it is not a cold-prevention supplement for most people.
Is there a vitamin C claim specifically for athletes?
Yes. The EU authorises the claim that vitamin C contributes to maintaining the normal function of the immune system during and after intense physical exercise — but only when daily intake is 200 mg above the normal recommended intake. If you train hard regularly, making sure your total daily intake exceeds that threshold is a reasonable nutritional goal.
How much vitamin C do I need each day?
The EU Nutrient Reference Value (NRV) is 80 mg per day, which most people can cover easily through diet. Rich sources include red peppers, kiwi, citrus fruits, berries, broccoli and Brussels sprouts. A couple of servings of these foods typically gets you there without needing a supplement at all.
Can I take too much vitamin C?
Because vitamin C is water-soluble, excess is excreted rather than stored, so the risk of toxicity is low. That said, very high doses above around 1,000 mg per day can cause digestive discomfort, diarrhoea and stomach cramps. There's no evidence that megadosing delivers extra benefit beyond meeting your daily needs, so more is not better here.