Vitamin C: what it does and how much you actually need

Vitamin C keeps your immune system, skin and blood vessels working properly, and it’s a job your body can’t do on its own, so you need a little every day from food. Its main roles are supporting your immune system, helping you make collagen (important for skin, gums, blood vessels and connective tissue), improving how well you absorb iron from plant foods, and acting as an antioxidant that protects your cells. The good news: a varied diet with some fruit and veg covers it easily, and for most people a supplement isn’t needed.

What vitamin C does in your body

Vitamin C (also called ascorbic acid) is water-soluble and plays a part in dozens of processes. Four stand out:

• Immune support: it helps your immune system work normally. Your white blood cells rely on it to do their job.
• Collagen and skin: your body needs vitamin C to make collagen, the “cement” of your skin, gums, blood vessels, cartilage and bones. It also helps wounds heal.
• Iron absorption: it improves how much iron you take up from plant sources like beans, lentils and leafy greens, which is handy if you eat little or no meat.
• Antioxidant: it protects your cells from damage by free radicals and helps recycle vitamin E.

Because vitamin C is water-soluble, your body doesn’t store it the way it stores fat-soluble vitamins. Any excess is mostly passed out in your urine, which is exactly why a steady daily supply from food matters.

How much vitamin C do you need a day?

For adults in the UK, the NHS puts the daily requirement at around 40 mg. Some other bodies set it a bit higher, but either way it’s an amount you get from ordinary food without trying: a single orange or half a red pepper already sails past it.

A few situations where your needs are higher:

• Smoking: smokers use up vitamin C faster and need more than non-smokers.
• Pregnancy and breastfeeding: the requirement is slightly higher.

Athletes are often told they need “far more”. In practice, a varied diet with enough fruit and veg covers most active people just fine. A mega-dose gives no measurable performance benefit.

How to spot a vitamin C shortfall

A severe deficiency is called scurvy, and in the UK it’s rare. It only develops after weeks to months on almost no vitamin C at all. Signs include bleeding, inflamed gums, poor wound healing, easy bruising, tiredness and joint pain. This really belongs to long-term, serious undernutrition rather than a normal diet.

Far more relevant for most people is a mild shortfall. You see it more often in people who eat little fruit and veg, in smokers, or in those who drink a lot of alcohol. A mild shortfall usually gives vague symptoms like tiring more easily or feeling run down, but those can have plenty of other causes too. Want certainty? Speak to your GP; a blood test can give you a clear answer.

Which foods are high in vitamin C?

Vitamin C lives mainly in fruit and vegetables. Good sources include:

• Citrus fruit: oranges, satsumas, lemons, grapefruit.
• Peppers: red peppers especially are a top source, with more vitamin C than an orange.
• Kiwi: small but rich in it.
• Broccoli, Brussels sprouts and cauliflower.
• Strawberries, blackcurrants and other berries.
• Potatoes: not huge per 100 g, but since we eat a fair amount of them they still add up.

One thing to know: vitamin C is sensitive to heat and water. Boiling for a long time loses some of it. Steam your veg briefly, or eat more of it raw, and you keep more of the goodness. Two portions of fruit and enough veg a day already put you comfortably above the recommended amount.

When is a vitamin C supplement worth it?

For most people who eat fruit and veg every day, a supplement isn’t needed. You get enough from food, and the excess is passed out anyway. A supplement can be worth it if:

• you consistently eat very little fruit and veg;
• you smoke and your diet is on the thin side;
• you’re going through a spell with little variety in your food (after illness, say).

In those cases a modest supplement works fine as a safety net. There’s no need to reach for the highest-dosed tub on the shelf; a dose around your daily requirement up to a few hundred milligrams is plenty. On price, plain vitamin C is one of the cheapest supplements going, so you never need to pay a premium to cover a gap. Not sure whether a supplement suits you? Have a look at our guide to the best vitamin and mineral supplements for a wider view.

Dose and upper limit: how much is too much?

Vitamin C is safe across a wide range. Even so, there’s a ceiling. The NHS advises that taking less than 1,000 mg a day from supplements is unlikely to cause harm for adults. Go well above that and the problems build up, mostly in your gut.

What happens if you take too much? Because vitamin C is water-soluble, you pass most of the excess out. But before it gets that far, a big single dose can bring on gut trouble: bloating, cramps and diarrhoea. Your body also absorbs high doses less and less efficiently. If you’re prone to kidney stones it’s sensible to be cautious with very high doses, so talk to your doctor first.

The practical lesson: more isn’t better. A dose around, or just above, your daily requirement does what it needs to. Mega-doses of thousands of milligrams give no extra health gain and only raise the odds of an upset stomach.

Does vitamin C really help against colds?

This is the most stubborn claim around vitamin C, and the honest answer has some nuance. For the average person, vitamin C doesn’t prevent colds. Whether or not you take extra, you’ll catch roughly the same number.

What does show up in research: in people who take extra vitamin C regularly (daily, not just once they’re already ill), a cold seems to run a little shorter and a bit milder on average. It’s a modest effect, not a miracle cure. Starting to take it the moment you feel a sniffle coming on barely helps.

In short: vitamin C isn’t a shield against colds, but for people who get it in steadily, a cold may run slightly shorter and milder. The real payoff isn’t a pill you grab the second you sneeze; it’s a diet that gives you enough vitamin C all year round.

Forms of vitamin C: ascorbic acid or buffered?

You’ll see different forms on the label. The main ones:

• Ascorbic acid: the most common and best-researched form. Effective and cheap. It’s mildly acidic, which can cause some stomach discomfort in sensitive people on an empty stomach.
• Buffered vitamin C (sodium or calcium ascorbate, for example): a less acidic form that some people find easier on the stomach. In practice the effect on your vitamin C level is comparable to plain ascorbic acid.
• Ester-C and forms with bioflavonoids: sold at a higher price with claims about better absorption. For most people the added value over plain ascorbic acid is small.

For most people, plain ascorbic acid is fine. If you have a sensitive stomach, a buffered form can be more comfortable. You don’t need to pick the priciest version to get the effect.

When is the best time to take vitamin C?

The timing matters less than many people think. A few practical points:

• With a meal: taking it during or after food lowers the chance of stomach discomfort, especially with ascorbic acid.
• With iron-rich meals: if you want to improve iron absorption from plant food, take your vitamin C alongside that meal (a glass of orange juice with your beans or lentils, for instance).
• Split through the day: if you take a higher dose, it’s absorbed better split into two smaller amounts than in one big one.

Don’t overcomplicate it. The main thing is getting enough in every day; the exact moment is a side note.