Vitamin C
The vitamin everyone reaches for at the first sign of a cold.
- Colds and winter bugs
- Blood pressure
- Blood sugar
- Exercise recovery
- Pregnancy
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
Compare vitamin C prices per dose
On this page
What is vitamin C?
Vitamin C, or ascorbic acid, is a vitamin the body cannot make and cannot do without: it is the helper that lets the body build collagen, the protein that holds skin, gums, tendons and blood vessel walls together, and it is one of the body’s main antioxidants. It comes from fruit and vegetables, and a shortage is rare in the UK. As a supplement it is sold as plain ascorbic acid, as gentler buffered salts such as calcium or sodium ascorbate, as fizzy or chewable tablets, and in liposomal form, where the vitamin is wrapped in tiny fat particles. It is probably the best-known supplement there is, and colds are the reason most people keep a tube of it in the cupboard.
Why do people take vitamin C?
Colds and winter bugs
The thinking. White blood cells pile vitamin C up inside themselves, holding many times the level in the blood, and use it up quickly during an infection. So taking extra at the first tickle of a cold is by far the most popular reason for having it in the house, and some people take it every day through winter instead.
What research has found. A large Cochrane review of trials in the general population found that taking vitamin C every day did not change how many colds people caught, but did make colds a little shorter, by around 8 per cent in adults and 14 per cent in children; starting it only once a cold had begun made no clear difference. Trials that gave it to adults with COVID-19 mostly found no clear change in how long symptoms lasted or in deaths. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Blood pressure
The thinking. Vitamin C helps the lining of blood vessels make nitric oxide, the signal that lets them relax, so a small effect on blood pressure has a clear mechanism behind it. It is rarely why people start taking vitamin C, but it is the effect with the most trial evidence.
What research has found. Three meta-analyses of randomised trials in adults with normal or raised blood pressure all found a reduction in the upper reading, of around 3 to 4 mmHg on average, mostly with about 500 mg a day. This is one of the best-studied uses, and several reviews of trials broadly agree.
Blood sugar
The thinking. People with type 2 diabetes tend to have lower vitamin C levels, and oxidative stress is part of the harm that high blood sugar does, so researchers have tested whether topping up helps the numbers.
What research has found. Two meta-analyses of trials in adults with type 2 diabetes measured blood glucose, HbA1c and insulin. One found better HbA1c and blood pressure; the other found no overall change in glucose or insulin. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.
Exercise recovery
The thinking. Hard exercise produces a burst of free radicals, and vitamin C is an antioxidant, so gym-goers and runners take it hoping to feel less sore and recover faster.
What research has found. Two meta-analyses of trials in healthy adults after exercise measured markers of inflammation and oxidative stress along with soreness and strength. The markers moved inconsistently, and soreness and strength did not clearly differ from placebo. Results here go both ways, which usually means the dose, the length of a trial or the group taking part makes the difference.
Pregnancy
The thinking. Vitamin C is needed for collagen, the protein that holds tissues together, which is why it was tested against pregnancy complications; it is in most pregnancy multivitamins anyway.
What research has found. A large review of trials in pregnant women found no clear overall difference in stillbirth or preterm birth. Two trials in pregnant women who smoked found better lung function in their babies, still measurable at five years old. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
What does vitamin C do in the body?
Humans are one of the few animals that cannot make vitamin C, so it has to come from food. Inside the body it does two main jobs: it is the helper that lets the enzymes building collagen do their work, and it is an antioxidant, mopping up the reactive molecules that cells make when they burn fuel or respond to infection. At very high doses it can tip the other way and act as a pro-oxidant, which is one reason more is not always better.
White blood cells hoard it, holding many times the level found in blood, and use it up during an infection, which is where the cold folklore comes from. The kidneys keep blood levels within a narrow band: once you take more than a few hundred milligrams at a time, absorption falls and the surplus leaves in the urine within hours, which is why very large doses mostly end up in the loo and, in some people, loosen the bowels on the way.
What do people say about taking vitamin C?
These are anecdotes people have shared, not evidence.
What people like
- Vitamin C is very commonly the thing people reach for the moment they feel run down or sense a cold starting, usually alongside zinc or echinacea, plenty of fluids and an early night. Many say it helps them get through the week, while freely admitting they cannot be sure which part of the routine did the work.
- People who take a tablet every day often say they seem to pick up fewer colds than they used to, with the honest caveat that it could just as easily be placebo, better sleep or more fruit and veg.
- Some who dissolve a fizzy tablet each morning say they feel a little brighter, though those products usually contain B vitamins too, and some say the pleasant taste is the only reason the habit sticks.
- Value is a recurring bright spot: people are pleased to find supermarket own-label versions at a fraction of the price of well-known names, with no difference in taste or effect.
Common complaints
- The most confident voices in these threads are the sceptics. Their line is that unless you are genuinely short of vitamin C, a supplement changes nothing you will notice, any excess simply leaves the body, and the money would be better spent on oranges and peppers.
- People who push the dose up often report loose stools, cramping or nausea, and take that as the practical ceiling, backing off until their gut settles.
- Chewable and effervescent tablets are acidic, and warnings about tooth enamel come up repeatedly, including advice relayed from a dentist; chewables also draw complaints about sugar, and plain ascorbic acid on an empty stomach gives some people heartburn.
- A minority mention that liposomal versions cost many times more than plain powder and question whether the absorption claims justify the price.
How people take it
- The single most common pattern is short-burst use: start at the first tickle of a cold, take it for a few days with zinc and echinacea, and stop once well again. Daily year-round use tends to be a fizzy tablet dissolved in water with breakfast, usually whichever cheap own-label the supermarket stocks.
- People who take larger amounts split the dose across the day and settle at whatever level their stomach tolerates, favouring cheap powder over tablets.
- The rough logic on form: plain ascorbic acid when cost is the priority, a buffered ascorbate when the acid is harsh on the stomach, and liposomal only for the few persuaded by the absorption claims.
- To protect teeth, people who chew or dissolve their vitamin C suggest rinsing with water afterwards, not brushing straight away, or switching to a capsule they swallow.
Read from these public discussions:
- Can you kill a cold before it takes? (Mumsnet, 2026)
- Do effervescent vitamin tablets really work? (Mumsnet, 2019)
- does chewable vitamin c really work? (AnandTech forums, 2014)
What forms of vitamin C are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Standard (ascorbic acid and ascorbates) | Ascorbic acid itself, or a salt such as calcium or sodium ascorbate, sometimes buffered or slow release. | 40 mg to 1.5 g |
| Liposomal | Ascorbic acid encapsulated in fat-based particles called liposomes. | 1 g |
What else is worth knowing about vitamin C?
- Trials on colds used at least 200 mg a day; blood-pressure trials mostly used 500 mg a day.
- Loose stools and stomach upset are the side effects reported at high doses; absorption falls off above a few hundred milligrams at a time, so a large dose is mostly passed straight through.
- Effervescent and chewable forms are acidic and may contain sugar and sodium, which the label will list.
- Labels give the vitamin C amount per tablet; a serving may be more than one, and the products we list run from 40 mg to 1.5 g per serving.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (18 studies)
- Ascorbic acid metabolism and functions: A comparison of plants and mammals. (2018, review)
- Vitamin C and Immune Function. (2017, review)
- Vitamin C-Sources, Physiological Role, Kinetics, Deficiency, Use, Toxicity, and Determination. (2021, review)
- Vitamin C for preventing and treating the common cold. (2013, meta-analysis)
- Vitamin C supplementation for COVID-19: an updated systematic review and meta-analysis. (2026, meta-analysis)
- Vitamin C for COVID-19: a systematic review and meta-analysis of randomised controlled trials. (2024, meta-analysis)
- Effect of vitamin C on mortality and symptom duration in COVID-19: a meta-analysis. (2021, meta-analysis)
- Effect of High-Dose Zinc and Ascorbic Acid Supplementation vs Usual Care on Symptom Length and Reduction Among Ambulatory Patients With SARS-CoV-2 Infection: The COVID A to Z Randomized Clinical Trial. (2021, randomised trial)
- Vitamin C supplementation and blood pressure: an updated systematic review and meta-analysis. (2026, meta-analysis)
- Effects of vitamin C supplementation on blood pressure: a dose-response meta-analysis of randomised controlled trials. (2026, meta-analysis)
- Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials. (2012, meta-analysis)
- Effects of vitamin C supplementation on glycemic control and cardiovascular risk factors in people with type 2 diabetes: a GRADE-assessed systematic review and meta-analysis of randomized controlled trials. (2021, meta-analysis)
- The effect of vitamin C supplementation on glycemic control in type 2 diabetes: a meta-analysis of randomized controlled trials. (2017, meta-analysis)
- Vitamin C supplementation and exercise-induced muscle damage and recovery: a systematic review and meta-analysis. (2026, meta-analysis)
- Effect of vitamin C supplementation on exercise-induced oxidative stress and inflammation: a meta-analysis. (2020, meta-analysis)
- Vitamin C supplementation in pregnancy. (2015, meta-analysis)
- Vitamin C supplementation in pregnant smokers and offspring lung function at 5 years: a randomised trial. (2023, randomised trial)
- Vitamin C supplementation for pregnant smoking women and pulmonary function in their newborn infants: a randomized clinical trial. (2014, randomised trial)
How much does vitamin C cost?
That depends on the form and the pack, so we work out the price of the same dose of every vitamin C product we can find and rank them.