Vitamin C Explained: The Everyday Nutrient Most of Us Think About Only in Winter

Vitamin C has a reputation problem. For most people it lives in a mental box labelled "take when you feel a cold coming on" — a nutrient you reach for reactively, in October, in effervescent tablet form, and then forget about until the following autumn.

That framing undersells it considerably. Vitamin C is involved in processes that run continuously in the body, from the structure of your skin to how efficiently you absorb iron from your dinner. And unlike some nutrients, your body has no meaningful way to stockpile it — which makes what you do every day far more relevant than what you do during a sniffle.

Here's a plain-English look at what this nutrient actually does, how much you need, and what to consider if you're thinking about supplementing.

Why humans need it at all

Most animals make their own vitamin C. Dogs, cats, cows and rats all synthesise it internally from glucose and never need to think about dietary sources. Humans, along with guinea pigs, bats and other primates, lost that ability somewhere in our evolutionary past through a mutation in a single enzyme.

The consequence is that we have to obtain it from food — and history records what happens when we don't. Scurvy, the disease that killed more sailors on long voyages than storms or combat, is severe vitamin C deficiency. Without the nutrient, the body cannot properly build collagen, and the tissue that holds us together begins to fail: gums bleed, wounds stop healing, old injuries reopen. It was a Royal Navy surgeon, James Lind, who ran one of the first controlled clinical trials in 1747, and found that citrus fruit resolved it.

Scurvy is rare in the UK today, but it hasn't disappeared. Cases still appear among people with very restricted diets, and it remains a useful illustration of how fundamental this nutrient is to basic bodily maintenance.

What it does, in practice

Under UK regulations, only specific health claims about vitamin C are permitted, and they're deliberately precise. The authorised statements include that vitamin C:

• contributes to normal collagen formation for the normal function of skin, bones, cartilage, gums, teeth and blood vessels
• contributes to the normal function of the immune system
• contributes to the protection of cells from oxidative stress
• contributes to normal energy-yielding metabolism
• contributes to the reduction of tiredness and fatigue
• contributes to normal psychological function and the normal functioning of the nervous system
• increases iron absorption

Two of those are worth expanding on, because they're the ones people tend to know least about.

Collagen. Collagen is the most abundant protein in the human body — the scaffolding in skin, tendons, blood vessel walls and the tissue around your joints. Vitamin C is required as a cofactor for the enzymes that stabilise collagen's structure. Without adequate vitamin C, the body can still produce collagen, but not properly formed collagen. This is precisely why scurvy presents the way it does, and it's the mechanism behind vitamin C's persistent presence in skincare discussions.

Iron absorption. This one has real practical value, particularly for anyone eating a plant-based or largely vegetarian diet. Iron from plant sources — beans, lentils, spinach, fortified cereals — is absorbed considerably less efficiently than iron from meat. Vitamin C consumed in the same meal improves that absorption substantially. In practice, that means squeezing lemon over a lentil dish, or having a satsuma alongside a bowl of fortified breakfast cereal, is a genuinely useful habit rather than a nutritional footnote.

And the cold question

It would be odd to write about vitamin C and skip the association everyone already has. So, honestly: the research here is more nuanced than the popular reputation suggests.

The idea took hold largely through the advocacy of Linus Pauling, a Nobel laureate chemist who became convinced of high-dose vitamin C's benefits in the 1970s. Decades of subsequent trials have produced a more measured picture. Broadly, the evidence does not support the notion that taking vitamin C once symptoms have already started changes much, and the strongest signals have been found in people under considerable physical stress — marathon runners, skiers, soldiers on exercises in cold conditions — rather than in the general population.

What the UK regulations permit saying is simply that vitamin C contributes to the normal function of the immune system. That's a statement about maintaining normal function, not about preventing or treating illness — and it's a fair summary of where the evidence sits. A nutrient your immune system requires to work normally is worth having consistently, which is rather different from a remedy you take when you feel rough.

How much do you actually need?

The UK reference nutrient intake for adults is 40mg a day — a figure that surprises people, because it's modest. A single medium orange gets you there. So does half a red pepper, a handful of strawberries, or a decent portion of broccoli.

Nutrition labels on supplements often reference the Nutrient Reference Value of 80mg, which is the EU-derived figure used for labelling purposes. Either way, the amounts involved are easily reached through food for most people eating a reasonably varied diet.

Where supplements at much higher doses are concerned — the 500mg and 1000mg products that fill supplement shelves — it's worth knowing that vitamin C is water-soluble. Absorption efficiency falls as the dose rises, and what the body doesn't use is excreted. UK guidance notes that supplemental doses above about 1000mg a day may cause stomach pain, wind and diarrhoea in some people. More is not straightforwardly better.

If you're choosing a supplement

A few things genuinely differ between products:

Form. Plain ascorbic acid is the standard and is well absorbed. Buffered forms — calcium or sodium ascorbate — are less acidic and are sometimes chosen by people who find plain ascorbic acid uncomfortable on an empty stomach. Liposomal and time-release formats are marketed on absorption grounds; the independent evidence for meaningful real-world advantage is thinner than the marketing suggests.

Dose. For general daily use, doses in the low hundreds of milligrams comfortably exceed requirements. Very high doses are unnecessary for most people.

Additions. Vitamin C is often combined with zinc, rosehip or bioflavonoids. Whether that's useful depends on what else you're taking — worth checking you're not doubling up if you also use a multivitamin.

Certification. Look for products made to recognised manufacturing standards, with clear labelling of the amount per serving rather than per "portion" of several tablets.

The practical takeaway

Vitamin C isn't a winter product. It's involved in collagen formation, iron absorption, energy metabolism and immune function every day of the year, and because the body doesn't store it, consistency matters more than intensity. For most people eating varied food, requirements are met without much thought. For those whose diets are narrower, who eat little fresh produce, or who are working to improve iron intake from plant sources, a modest daily supplement is a reasonable and inexpensive thing to consider.

If you have a health condition, are pregnant, or take prescribed medication, check with your GP or pharmacist before starting any supplement.

Food supplements are not a substitute for a varied and balanced diet or a healthy lifestyle. This article is general information and not medical advice.