Vitamin C

Vitamin C (ascorbic acid) is needed to make collagen, the protein that holds skin, blood vessels, gums, bones, and tendons together. It is also an antioxidant, helps the body absorb iron from plant foods, and supports normal immune function. Unlike most animals, humans cannot make vitamin C internally and must get it from food.

The body holds modest stores of vitamin C, perhaps a few weeks of supply. After that, signs of deficiency develop. The full deficiency picture, scurvy, was the disease that killed sailors on long voyages before fresh fruit was carried. It is rare in modern UK life but is reported in people with very narrow diets, in heavy alcohol use, in chronic mental illness, and occasionally in babies fed only on cow's milk.

Vitamin C and iron: non-haem iron, the form in plant foods, fortified cereals, eggs, and pulses, is absorbed inefficiently on its own. Vitamin C in the same meal converts it to a more absorbable form. The practical effect is real: a squeeze of lemon on dhal, peppers in a stir-fry with tofu, or a glass of orange juice with a bowl of fortified cereal can roughly double iron absorbed from that meal. See the Iron entry for the full pairing.

Cooking and storage: vitamin C is degraded by heat, light, and air. Long boiling, then discarding the cooking water, removes a lot of vitamin C from vegetables. Steaming, microwaving, stir-frying, or eating raw retains most of it.

Vitamin C is concentrated in fruit and vegetables. A single portion of a vitamin C-rich food easily exceeds the 40mg adult daily target. Values per 100g come from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only.

The "5 a day" framing exists in part because of vitamin C: hitting five portions of varied fruit and vegetables makes meeting the vitamin C target almost automatic, and tends to bring fibre, folate, potassium, and several other nutrients along with it.

UK Reference Nutrient Intake (RNI) for vitamin C is set by SACN (1991 Dietary Reference Values).

Smokers have higher vitamin C turnover and lower blood levels at the same intake. The UK reference is the same, but stopping smoking is the bigger health move than topping up vitamin C.

Vitamin C deficiency runs along a spectrum from "low intake, no obvious symptoms" to scurvy. Scurvy itself is rare in modern UK life but does still appear in people with very restricted diets, severe alcohol use, severe mental illness, and (rarely) in babies fed only on unfortified cow's milk.

Early signs of low intake:

• Tiredness, low mood, irritability
• Easy bruising
• Slow wound healing
• Dry, splitting hair
• Rough or bumpy skin (often on the back of the upper arms)

Established scurvy adds:

• Swollen, bleeding gums; loose teeth in long-running deficiency
• Joint pain, including in the legs
• Small red or blue spots on the skin around hair follicles (perifollicular haemorrhages)
• Anaemia
• Severe fatigue

Who is at higher risk in the UK

• People with very limited diets (very few fruit or vegetables across weeks or months)
• People dependent on alcohol
• People with anorexia or other severe restrictive eating
• Some older adults living alone with little access to or appetite for fresh produce
• People with malabsorption conditions (coeliac disease, Crohn's, ulcerative colitis)
• People who smoke heavily (turnover is higher)
• Babies fed only on cow's milk without fortified solids or vitamin drops

Treatment of confirmed deficiency is straightforward: vitamin C from food, typically supported by a short course of supplements at higher dose under medical advice, brings most symptoms back within weeks.

Vitamin C from food is not a realistic risk: the body excretes the excess in urine.

NHS supplement guidance: taking large amounts of vitamin C, more than 1,000mg a day, can cause stomach pain, diarrhoea, and flatulence. Symptoms settle on stopping.

Very high doses have been suggested in popular wellness writing as a treatment for colds. The evidence has been reviewed many times. Routine supplementation does not seem to prevent colds in the general population but may shorten their duration slightly. The dose required for any effect (1,000mg or more) brings gut side effects, and the NHS does not recommend routine high-dose use.

People with iron overload conditions (such as hereditary haemochromatosis) should avoid high-dose vitamin C supplements, because vitamin C increases iron absorption.

Most UK adults eating any reasonable mix of fruit and vegetables hit the 40mg vitamin C target without thinking about it. Supplementation is not routinely recommended.

When a supplement may be sensible:

• Confirmed deficiency or scurvy (under medical advice).
• Very limited dietary access to fruit or vegetables, while the underlying situation is being addressed.
• Some absorption conditions, on personalised advice.

Tips for keeping vitamin C in food:

• Eat fruit raw where possible.
• Steam or microwave vegetables instead of long boiling. Or stir-fry briefly.
• If you do boil, the cooking water carries away much of the vitamin C; use it in stock or sauce where you can.
• Chop close to eating rather than hours ahead.

• The iron absorption pairing: Iron. Vitamin C with a non-haem iron meal makes a meaningful difference.
• Vitamin C as a food additive: E300 ascorbic acid is widely used as an antioxidant on UK labels.
• UK official position on fruit and veg in practice: The Eatwell Guide.
• Best food sources: Blackcurrants, Peppers, Oranges, Kiwifruit, Broccoli.

• NHS. Vitamins and minerals: Vitamin C. nhs.uk/conditions/vitamins-and-minerals/vitamin-c. Adult RNI, food sources, supplement guidance, upper level.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report 41 (1991). Source of the age-banded RNIs.
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).
• USDA Agricultural Research Service. FoodData Central, SR Legacy release. fdc.nal.usda.gov.

This page is reference information for UK shoppers. It is not medical advice.