Vitamin C: benefits, deficiency and foods rich in it

What vitamin C does

Vitamin C, or ascorbic acid, is a water-soluble vitamin the body cannot make or store in quantity, so it depends on what you eat each day. Its most important function — and the one that tends to surprise people — is that it is required to make collagen, the protein that acts as the "scaffolding" of the whole body: it gives structure to skin, gums, bones, cartilage and the walls of blood vessels. Without vitamin C, that scaffold weakens, which is why a shortfall shows up so quickly in bleeding gums and wounds that will not close. On top of that, vitamin C is an antioxidant that protects cells from oxidative damage, supports normal immune function, is involved in making some neurotransmitters, and enormously boosts the absorption of plant iron. A broad CV for a vitamin almost everyone reduces to "the cold thing".

The symptoms of deficiency

Because the body keeps barely any reserves of vitamin C, a very low intake shows up within weeks or a few months. The classic severe deficiency is scurvy, rare today but not gone:

• Inflamed, tender gums that bleed easily.
• Bruises that appear at the slightest knock (fragile vessels).
• Cuts and wounds that take a long time to close.
• Intense fatigue, weakness and irritability.
• Joint and muscle pain.
• Dry, rough skin; in advanced cases, loss of teeth.

Who is most at risk

On a diet with some fresh fruit and vegetables, reaching deficiency is hard, but there are higher-risk situations. People on very restrictive or monotonous diets (little or no fruit and veg), those with disorders that impair absorption, people with alcohol or substance dependence, and those in isolation or food poverty. Smokers deserve a special mention: tobacco increases the body’s use of vitamin C, so their needs are somewhat higher. Pregnancy and breastfeeding also raise requirements a little. Recognising yourself in one of these groups does not mean you are deficient, but it does mean paying more attention to eating fruit and veg every day.

Where vitamin C is (and how not to destroy it)

The big myth is that vitamin C is "an orange thing". In reality it is widely spread across fresh fruit and vegetables, and some foods far outdo the citrus. Red pepper is one of the champions; kiwi, strawberries, broccoli, Brussels sprouts, papaya and mango are excellent; and citrus, tomato and potato all contribute. The detail almost nobody accounts for is that vitamin C is fragile: it degrades with heat and dissolves into cooking water, so boiling for a long time can pour much of it down the drain. The fix is simple: eat some of your vegetables raw or barely cooked, favour steaming or a quick saute over long boiling, and do not leave cut fruit exposed to air for hours.

Vitamin C and iron: the pairing that really works

Of all vitamin C’s functions, the most practical in daily life is its role as an iron booster. The iron in plants (non-heme iron, found in legumes, spinach, tofu or wholegrains) is absorbed quite poorly on its own. Vitamin C converts it into a form the gut takes up much better, so a single meal can give you several times more usable iron just by combining it well. The trick is as simple as adding a source of vitamin C to iron-rich plant dishes: a pepper in the lentil salad, a tomato with the spinach, a squeeze of lemon over the beans, or an orange for dessert. For anyone on a vegetarian or vegan diet, or prone to anaemia, this small habit is one of the most effective levers there is. We develop it in our guide on iron deficiency.

Vitamin C and colds: what the evidence says

This is the most deeply rooted myth of all, so it is worth being clear and honest. The largest systematic reviews, pooling dozens of studies, agree on two points. First: taking vitamin C regularly does NOT reduce your chances of catching a cold in the general population — it does not prevent colds, however much it is sold that way. Second: in those who already take it daily, colds may last a little less or be somewhat milder, a real but small effect; and starting to take vitamin C once you are already ill has shown no clear benefit. The one notable exception is people under extreme physical stress (marathon runners, skiers, soldiers in the cold), where it does appear to reduce incidence. For the rest of us, vitamin C is not the anti-cold shield of the advertising.

When (and how much) to supplement

For the vast majority of people, the answer is simple: there is no need to supplement. A few portions of fruit and vegetables a day cover vitamin C comfortably, and the body flushes out what it does not use. Supplementing makes sense in specific cases: very restrictive diets with hardly any vegetables, certain absorption problems, or situations assessed by a professional. If at some point you do take a supplement — for example during a spell of a very poor diet — moderate doses close to the daily recommendations are more than enough; there is no advantage in bottles of megadoses. And a bottom-line idea we repeat with every micronutrient: a supplement does not fix a poor diet. Before buying vitamin C, the useful question is how much fruit and veg you are actually eating.

Vitamin C is the perfect example of why looking at your real diet beats trusting a bottle, and this is where Renzy helps without you keeping counts by hand. By photographing your meals you see at a glance how much fresh fruit and veg enters your week — the natural sources of vitamin C — and you spot whether your pattern falls short without noticing. With that data you can do what actually works: add a pepper, a kiwi or some strawberries, and place them next to the legumes or spinach to squeeze out their iron too. Because with vitamin C, as with almost everything, a well-chosen plate beats the jar of capsules.