Also known as: Ascorbic acid, L-ascorbic acid, Sodium ascorbate, Liposomal vitamin C, Ester-C
VitaminsStrong evidence
An essential water-soluble vitamin required for collagen synthesis, immune function and iron absorption. Absorption saturates at modest intakes, which makes the very high doses common in this category largely pointless.
Typical dose
200.0–1000.0 mg per day
With food; split if taking more than 500 mg
What it is
Vitamin C is a water-soluble essential nutrient. Humans, unlike most mammals, cannot synthesise it, having lost the necessary enzyme through an ancestral mutation, so it must come from diet.
Rich sources include citrus, blackcurrants, peppers, broccoli and strawberries. Reference intakes are modest, and shortfall is uncommon in the UK, though marginal status occurs in smokers and in people with limited fruit and vegetable intake.
Forms include plain ascorbic acid, buffered mineral ascorbates that are gentler on the stomach, and liposomal preparations claiming improved absorption at higher doses. For most people plain ascorbic acid at a sensible dose is entirely adequate, and the premium forms address a problem most users do not have.
How it works
Vitamin C acts as an enzyme cofactor, most importantly for the enzymes that modify collagen as it is built. Without it, collagen cannot form a stable structure, which is why long-term shortfall shows up first in connective tissue.
It is a potent water-soluble antioxidant, donating electrons to neutralise reactive species and regenerating vitamin E from its oxidised form.
It also converts dietary iron from plant sources into a more absorbable form, substantially improving uptake, and accumulates in immune cells where it supports several aspects of their function. Absorption is transporter-mediated and saturable, which is why efficiency falls sharply as dose rises.
What the evidence shows
Its role as an essential nutrient is beyond dispute. The more contested question is what supplementation achieves in people who are not deficient.
On the common cold, the evidence is well characterised and more modest than folklore suggests. Regular supplementation does not meaningfully reduce how often most people catch colds, though it shortens duration slightly. The exception is people under heavy physical stress, such as marathon runners and soldiers in extreme conditions, where trials have shown a substantial reduction in incidence.
Iron absorption enhancement is well established and practically useful. Worth knowing for athletes: high-dose antioxidant supplementation around training has been shown in several trials to blunt some adaptations to exercise, so more is not better in that context either.
Dosing
Plasma levels approach saturation at around 200-400 mg daily. Beyond roughly 1,000 mg, absorption efficiency falls considerably and most of the excess is simply excreted, which is the origin of the observation about expensive urine.
For most people 200-500 mg daily covers any plausible benefit. Doses of 1,000 mg are common and harmless but largely surplus to requirement. Splitting into two servings improves absorption if taking more.
Take alongside plant-based iron sources to improve absorption. If training for adaptation, avoid taking large doses immediately around sessions.
Approximately 2-4 hours; tissue saturation maintained by regular intake
Timing
With food; split if taking more than 500 mg
Competition status
Permitted — not on the WADA Prohibited List
Category
Vitamins
Safety and side effects
Vitamin C has an excellent safety record. Being water soluble, excess is excreted rather than accumulated. The main dose-limiting effect is digestive: doses above roughly 2,000 mg commonly cause diarrhoea, cramping and nausea.
High doses increase oxalate in the urine, which is relevant for anyone who has had kidney stones. Those individuals should keep intake modest.
Because it enhances iron absorption, high-dose supplementation is not advisable for anyone who has been told they retain too much iron. Very high doses can also interfere with some home blood monitoring devices.
Who should avoid it
Keep intake modest if you have a history of kidney stones. Avoid high doses if you have been told you retain too much iron. May interfere with some home blood monitoring devices at very high doses. Speak to your doctor before taking high doses if you are receiving any form of medical treatment.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
