Vitamin C doesn’t prevent colds for most people, and taking it only after a cold starts doesn’t seem to help. A Cochrane review of trials involving more than 11,000 people found that taking vitamin C regularly didn’t reduce how often people in the general population caught colds. It did shorten colds slightly, by about 8% in adults and 14% in children, which works out at roughly half a day for a typical week-long cold. The exception was people under heavy physical stress, such as marathon runners and soldiers in subarctic conditions, whose risk of catching a cold was roughly halved. For most people, getting enough vitamin C from food is what matters.
What the evidence shows
| Question | Answer from the Cochrane review |
|---|---|
| Does regular vitamin C prevent colds? | Not in the general population (risk ratio 0.97) |
| Does it help people under extreme physical stress? | Yes: about half the risk in 598 marathon runners, skiers and soldiers |
| Does regular vitamin C shorten colds? | Slightly: by 8% in adults and 14% in children |
| Does starting vitamin C when a cold begins help? | No consistent effect on how long or how bad colds are |
Why regular vitamin C might shorten colds a little
Vitamin C helps the immune system work normally, and immune cells contain high levels of it. But being well nourished isn’t the same as having extra protection. Once you have enough vitamin C, which most people get from a varied diet, taking more doesn’t give you a stronger defense against cold viruses. The small effect on cold duration may reflect better support for immune cells in people who take it regularly, but it’s too small for most people to notice.
How much vitamin C do you need?
The NHS says adults aged 19 to 64 need 40 mg of vitamin C a day, and that you should be able to get all you need from your diet. In the US, the recommended amounts are 75 mg for women and 90 mg for men, with an extra 35 mg for smokers. These are easy to reach with food:
| Food | Vitamin C |
|---|---|
| ½ medium red pepper (about 60 g) | about 75 mg |
| 1 kiwifruit (about 75 g) | about 70 mg |
| 1 medium orange (about 130 g) | about 70 mg |
| 80 g strawberries (about 7) | about 45 mg |
| 80 g broccoli, cooked | about 50 mg |
Values are calculated from USDA FoodData Central. Our list of vitamin C foods has more, and our guides to kiwi and bell peppers cover two of the best sources.
Is it safe to take high doses?
The NHS says taking large amounts, more than 1,000 mg a day, can cause stomach pain, diarrhea and flatulence, and that taking less than 1,000 mg a day of vitamin C supplements is unlikely to cause harm. High doses may also raise the risk of kidney stones in some people. If you have kidney disease, a history of kidney stones, or haemochromatosis (iron overload), talk to your doctor before taking vitamin C supplements.
What actually helps when you have a cold
Most colds get better on their own within about 1 to 2 weeks. To feel better:
- Rest and keep warm.
- Drink plenty of fluids, such as water, warm drinks and soups.
- Use painkillers such as paracetamol or ibuprofen if needed, following the label.
- Try a warm drink with lemon and honey to soothe a sore throat. Don’t give honey to babies under 1.
- Wash your hands often and catch coughs and sneezes in a tissue to avoid spreading it.
Antibiotics don’t work on colds, because colds are caused by viruses.
When to see a doctor
The NHS advises seeing a doctor if your symptoms last more than 3 weeks, get suddenly worse, you have a high temperature that doesn’t come down, chest pain or difficulty breathing, or you have a long-term condition such as diabetes, heart or lung disease. Get urgent help for breathing difficulties.
Supporting your immune system with diet
No single food or supplement protects you from colds, but a varied diet helps your immune system work normally:
- Plenty of fruit and vegetables for vitamin C, folate and other nutrients. Our guide on how to eat more vegetables has easy ideas.
- Protein foods, such as fish, eggs, beans, lentils and dairy.
- Vitamin D in winter, as many people run low. Our guide to vitamin D sources explains who needs a supplement.
- Zinc from meat, shellfish, dairy, beans and seeds.
- Enough sleep and regular activity.
Common questions
Should children take vitamin C?
The NHS recommends that children aged 6 months to 5 years are given vitamin supplements containing vitamins A, C and D every day, unless they drink more than 500 ml of infant formula a day. That’s to make sure young children get enough, not to prevent colds. Older children can usually get enough vitamin C from fruit and vegetables.
Is vitamin C from food better than supplements?
Food is the best source for most people, because fruit and vegetables also provide fiber and many other nutrients. Supplements are useful if your diet is very limited.
Should I take vitamin C if I exercise hard?
The Cochrane review found a lower cold risk in people doing intense, prolonged exercise in harsh conditions. If you train very hard, regular vitamin C from food, or a modest supplement, may be worth considering. Ask your doctor or a sports dietitian.
Are vitamin C drinks and fizzy tablets worthwhile?
They usually provide far more vitamin C than you need, and some contain sugar or a lot of sodium. Fruit and vegetables are a better source.
Does orange juice help a cold?
It provides vitamin C and fluid, but it’s high in free sugars. Our article on whether orange juice is healthy explains how much is sensible.
This article is general information, not medical advice. Talk to your doctor or a registered dietitian before making big changes to how you eat, especially if you have a health condition, take regular medication, or are pregnant or breastfeeding.
