What is vitamin C good for? What the studies show, how much you need and when extra becomes too much

In this article you will find the answer to the question of what vitamin C is good for: what vitamin C does in your body, how much you need and how much you already get, what large studies found about colds, the heart and diabetes, and when extra vitamin C becomes too much. That matters, because many people take a tablet every day without knowing whether their food already gives them enough. The BioProfile lifestyle scan asks what you eat each day and how you live, such as how often vegetables, fish and pulses are on your plate, and gives you an indication of where you stand today. This is not a diagnosis. It is insight into where you stand today, to help you make better choices about food and lifestyle. The scan does not measure how much vitamin C is in your blood and does not point to a cause. Only a doctor can assess that.

What vitamin C does in your body

As an antioxidant, vitamin C protects the body’s cells against damage. Vitamin C is needed to form connective tissue, the tissue that holds the body together, and helps the body absorb iron.⁠¹ The Dutch pharmacists’ website adds that vitamin C is needed for wounds to close properly, for the immune defences and for the blood.⁠⁵ Put simply, your body uses vitamin C every day to protect cells, build tissue and make use of iron.

If you search for ‘what is vitamin c good for skin’, you want to know what vitamin C does for your skin. The sources here are about wounds: wounds need vitamin C to close properly,⁠⁵ and with a deficiency, wounds close more slowly.⁠¹ Every source in this article is about vitamin C that you eat or swallow. A vitamin C serum on the skin is a separate question, and these sources do not answer it.

How the body ages at the level of your cells, and how that can differ from the age in your passport, is the subject of biological age versus calendar age.

How much you need and how much you get

In the Netherlands, the advice for adults aged 18 and over is 75 mg of vitamin C a day. For children aged 11 to 14, the advice is 45 mg. A portion of red pepper gives you 90 mg, an orange 66 mg and a portion of strawberries 60 mg.⁠¹

The 2019 to 2021 Voedselconsumptiepeiling, the Dutch national food consumption survey, found an average intake of 159 mg a day from food and supplements together, and 87 mg a day from food alone. Adults got more than children, and women more than men. The biggest sources were vegetables (24 per cent), fruit, nuts and olives (22 per cent), supplements (16 per cent) and soft drinks and juices (12 per cent).⁠²

What this means for you: on average, food alone already gives you more than the recommended amount. One orange brings an adult close to 75 mg, and one portion of red pepper already takes you past it.⁠¹

How you notice a deficiency

You first notice a deficiency through lower resistance and wounds that close more slowly. In the end it becomes scurvy, with bleeding gums.⁠¹ Extra vitamin C is meant for people with a deficiency, such as heavy drinkers and people who eat very little vegetables and fruit.⁠⁵ So the people most likely to run short first are those who rarely eat vegetables or fruit.

Vitamin C and colds

A Cochrane review brought the studies together. In 29 comparisons with 11,306 participants, people from the general population who took at least 200 mg a day did not get fewer colds. In 5 studies with 598 marathon runners, skiers and soldiers under heavy physical stress, taking vitamin C regularly halved the chance of a cold. With regular use, a cold lasted about 8 per cent shorter in adults and 14 per cent shorter in children. People who only started taking vitamin C once the cold had already begun saw no consistent effect.⁠³

Put simply: for most people, a daily tablet does not mean fewer colds, although a cold may clear up a little faster. The pharmacists’ website sums it up: an effect on colds has not been shown.⁠⁵

Vitamin C, the heart and living longer

A large review of prospective studies followed people for years and compared how much vitamin C they got from food. Every extra 100 mg a day from food went together with about a tenth less risk of coronary heart disease, of cardiovascular disease as a whole and of death from any cause, and with a slightly lower risk of stroke. People with more vitamin C in their blood also had clearly lower risks.⁠⁶

These are links seen in large groups of people. They do not prove that a supplement causes the lower risk.⁠⁶ The link was measured for vitamin C from food, and in the Netherlands vegetables and fruit are its biggest sources.⁠² What else changes in the body as the years go by is covered in healthy ageing: what changes over the years.

Vitamin C and diabetes

A review of 28 randomised trials involving 1,574 people with type 2 diabetes looked at vitamin C supplements. Systolic blood pressure, the upper number, fell by about 6 points, and the researchers had moderate confidence in that result. HbA1c, your long-term blood sugar value, and diastolic blood pressure, the lower number, also fell slightly, but the evidence for both was very weak, and most of the trials were short and small. The authors conclude that vitamin C supplements cannot currently be recommended as a therapy for type 2 diabetes until larger, longer, high-quality trials confirm the findings.⁠⁷

So the result for blood pressure is interesting, but the researchers themselves say it is too early to count on vitamin C for diabetes.

Every day, too much, and what not to combine

Most people get enough vitamins by eating healthily and spending enough time outdoors. Thuisarts names a few vitamins that some people need extra: vitamin D, vitamin B12 and folic acid. Vitamin C is not on that list. Getting too many vitamins can be dangerous.⁠⁸

In normal amounts, vitamin C has almost no unwanted effects. Above 1,500 mg a day, nausea or diarrhoea can occur.⁠⁵ The Voedingscentrum puts gut complaints above 2 grams a day and notes that no official upper limit has been set.⁠¹

A Swedish study followed 23,355 men aged 45 to 79 with no previous kidney stones for 11 years, and 436 of them developed a first kidney stone. Men who took vitamin C supplements had about twice the risk of men who took no supplements, and at 7 or more tablets a week the risk was slightly higher still. Taking a multivitamin showed no link with kidney stones.⁠⁴ For you, this means a daily high-dose tablet is less harmless than the tablet looks.

Extra caution is needed in three situations. Combining a lot of vitamin C with deferasirox, a medicine that binds iron, can damage the heart. People with G6PD deficiency should avoid high doses. People prone to kidney stones run a higher risk with high doses.⁠⁵

When to see your GP

A kidney stone stuck between the kidney and the bladder causes very severe pain in your side or belly. Usually the stone passes out with your urine by itself within a few hours to a few days. Contact your GP if painkillers do not help enough, if you get a fever during or after such an attack of pain, or if it hurts to pee.⁠⁹ If a doctor advises a higher dose than the one on the pack, follow the doctor’s advice.⁠⁸

In summary

Vitamin C protects cells, helps form connective tissue, helps the body absorb iron and helps wounds close. Most adults in the Netherlands already get more than the recommended 75 mg from food. For most people, a daily tablet does not mean fewer colds. More vitamin C from food goes together with a lower risk for the heart, and that link does not prove that tablets work. For type 2 diabetes the evidence is still too thin. High doses carry their own risks, such as kidney stones, and some medicines and conditions do not go well with them.