Vitamin C Benefits: What the Evidence Shows

Quick answer

Vitamin C benefits, in short: Vitamin C (ascorbic acid) is an essential vitamin found in fruit and vegetables. Most people can meet their needs from food. Taking it daily as a supplement did not reduce how many colds people got in the general population, but colds were about 8% shorter in adults and 14% shorter in children [1]. In short trials, vitamin C lowered systolic blood pressure by about 4 mmHg on average [2]. Very high doses mainly cause stomach upset [4][5]. We rate the evidence C: small benefits for some outcomes, none for others, and benefit mostly in particular groups.

What is vitamin C?

Vitamin C is a water-soluble vitamin that works as an antioxidant. Your body also needs it to make collagen, a protein involved in wound healing [4]. It cannot be stored, so you need it in your diet every day [5]. Good sources include citrus fruit, peppers, kiwifruit, broccoli, strawberries and potatoes [4][5]. Supplements usually contain ascorbic acid, and NIH says no form has been shown to be better than the others [4].

Official intake figures

• UK (NHS): adults aged 19 to 64 need 40 mg a day. Taking more than 1,000 mg a day can cause stomach pain, diarrhea and flatulence, and under 1,000 mg a day is unlikely to cause harm [5].
• US (NIH): the recommended amount is 90 mg a day for men and 75 mg for women, and 35 mg more if you smoke. The upper limit for adults is 2,000 mg a day from food, drinks and supplements combined [4].

Vitamin C benefits: what might it help with?

Possible benefit	Rating	In plain words
Length of colds (taken regularly)	Promising	Colds were 8% shorter in adults and 14% in children across trials [1]
Number of colds	Mixed	No change in the general population; fewer colds in people under extreme exercise stress [1]
Taking it after a cold starts	No clear benefit	No consistent effect in the few trials [1]
Blood pressure	Promising	An average 3.8 mmHg drop in systolic pressure in short trials [2]
Effect on gains from exercise training	No clear benefit	Vitamin C and/or E did not blunt training gains in 18 trials [3]

Ratings describe how good the research is, not a promise that it will work for you.

What the research says

• Colds (Cochrane review, 29 trial comparisons, 11,306 people). In general community trials, regular vitamin C did not change the number of people getting a cold (risk ratio 0.97). In 598 marathon runners, skiers and soldiers on subarctic exercises, colds were roughly halved (risk ratio 0.48). Regular use shortened colds by 8% in adults and 14% in children, and in children 1 to 2 g a day shortened colds by 18%. Taking vitamin C once a cold had started showed no consistent effect [1]. PubMed · DOI
• Blood pressure (29 trials). Median dose was 500 mg a day for 8 weeks. Systolic pressure fell by 3.84 mmHg and diastolic by 1.48 mmHg on average. The authors said longer trials with clinical events are needed [2]. PubMed · DOI
• Exercise training. In 9 trials of aerobic training and 9 of resistance training, vitamin C and/or E did not reduce gains in aerobic fitness, endurance, lean mass or strength. The authors called for larger studies [3]. PubMed · DOI
• Cancer and heart disease. NIH says vitamin C supplements, with or without other antioxidants, don’t seem to protect people from getting cancer, and it isn’t clear whether vitamin C from food or supplements protects against cardiovascular disease [4].

The key limits: the cold results are for regular daily use over a period, the blood pressure trials were short and small, and the evidence says nothing about long-term health.

Amounts and how people take it

These are amounts used in studies, not recommendations.

• Colds: the Cochrane review only included trials of at least 200 mg a day, and found a larger effect on cold length in children at 1 to 2 g a day [1].
• Blood pressure: a median of 500 mg a day for 8 weeks [2].
• Food first: both the NHS and NIH say a varied diet can supply what you need [4][5].
• Limits: the NHS says amounts above 1,000 mg a day can cause stomach symptoms [5], and NIH sets an upper limit of 2,000 mg a day for adults [4].

Side effects, interactions and who should check first

Large amounts can cause stomach pain, diarrhea, flatulence and nausea, which should stop when you stop taking it [4][5]. In people with hemochromatosis (a condition where the body stores too much iron), high doses could worsen iron overload [4].

Who should check with a doctor or pharmacist first

Check with a doctor or pharmacist first if you:

• have hemochromatosis or another iron storage condition [4]
• are being treated for cancer. NIH says vitamin C and other antioxidants might interact with chemotherapy and radiation [4]
• take a statin and niacin to control cholesterol. In one study, vitamin C with other antioxidants reduced their heart benefit [4]
• take any other regular medicine, or have a long-term health condition
• are pregnant or breastfeeding, or are giving it to a child. NIH lists lower upper limits for children [4]

Where to buy

Look for the active form and amount (vitamin C as ascorbic acid, in mg per serving), a stated third-party testing certificate you can check, and work out the price per daily dose rather than comparing pack prices.

FAQ

What is vitamin C good for?

Your body needs vitamin C to make collagen, a protein involved in wound healing, and it works as an antioxidant [4]. As a supplement, trials found colds were about 8% shorter in adults and 14% shorter in children with regular use [1], and blood pressure fell by about 4 mmHg in short trials [2]. We rate the evidence C.

Does vitamin C work?

It depends on the goal. Daily vitamin C did not reduce how many colds people got in the general population, though colds were shorter [1]. Systolic blood pressure fell by about 4 mmHg in short trials, and the authors called for longer studies [2]. Vitamin C and/or E did not blunt exercise training gains in 18 trials [3].

How much vitamin C per day?

Official amounts are for overall intake: 40 mg a day for UK adults aged 19 to 64 [5], and 90 mg for men and 75 mg for women in the US [4]. Studies used more: at least 200 mg a day in the cold review [1] and a median of 500 mg a day in the blood pressure trials [2]. These are study and guideline figures, not personal advice.

Who should not take vitamin C?

Check with a doctor or pharmacist first if you have hemochromatosis or another iron storage condition, are being treated for cancer, take a statin with niacin, take any regular medicine, or have a long-term condition [4]. Also check first if you are pregnant or breastfeeding, or giving it to a child, because NIH lists lower upper limits for children [4].

Can you take vitamin C with magnesium?

In the NIH and NHS pages we used for this page, we found no information on taking vitamin C with magnesium, so we can’t say either way. The interactions NIH lists involve chemotherapy and radiation, and a statin-niacin combination [4]. Ask a doctor or pharmacist before combining supplements, especially if you take any medicine.

Related pages

• Vitamin D
• Vitamin K2
• Beetroot
• Longevity supplements for beginners: where this fits in a beginner’s routine
• All supplements A-Z

Talk to your doctor

This page is for general information and is not medical advice. Speak to a doctor or pharmacist before starting any supplement, especially if you are pregnant or breastfeeding, take any medicine, or have a health condition.

References

We cite only studies and official pages we checked against PubMed, the publisher or the agency’s own site. The A to E evidence grades are explained in our editorial policy. See also our medical disclaimer and affiliate disclosure.

1. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013. PubMed · DOI
2. Juraschek SP, Guallar E, Appel LJ, et al. Effects of vitamin C supplementation on blood pressure: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012. PubMed · DOI
3. Clifford T, Jeffries O, Stevenson EJ, et al. The effects of vitamin C and E on exercise-induced physiological adaptations: a systematic review and Meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 2020. PubMed · DOI
4. National Institutes of Health, Office of Dietary Supplements. Vitamin C: Fact Sheet for Consumers. Updated 22 March 2021. NIH ODS
5. NHS. Vitamins and minerals: Vitamin C. Page last reviewed 3 August 2020. NHS