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Vitamin C is a water-soluble vitamin that has a number of biological functions.
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Our proprietary "Star-Rating" system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.
For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.
3 Stars Reliable and relatively consistent scientific data showing a substantial health benefit.
2 Stars Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1 Star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.
This supplement has been used in connection with the following health conditions:
How It Works
How to Use It
The recommended dietary allowance (RDA) for vitamin C in nonsmoking adults is 75 mg per day for women and 90 mg per day for men. For smokers, the RDAs are 110 mg per day for women and 125 mg per day for men. Most clinical vitamin C studies have investigated the effects of a broad range of higher vitamin C intakes (100-1,000 mg per day or more), often not looking for (or finding) the "optimal" intake within that range. In terms of heart disease prevention, as little as 100-200 mg of vitamin C appears to be adequate.1 Although some doctors recommend 500-1,000 mg per day or more, additional research is needed to determine whether these larger amounts are necessary. Some vitamin C experts propose that adequate intake be considered 200 mg per day because of evidence that the cells of the human body do not take up any more vitamin C when larger daily amounts are used.2
Some scientists have recommended that healthy people take multi-gram amounts of vitamin C for the prevention of illness. However, little or no research supports this point of view and it remains controversial. Supplementing more results in an excretion level virtually identical to intake, meaning that consuming more vitamin C does not increase the amount that remains in the body.3 On the basis of extensive analysis of published vitamin C studies, researchers at the Linus Pauling Institute at Oregon State University have called for the RDA to be increased, but only to 120 mg.4 This same report reveals that ". . . 90-100 mg vitamin C per day is required for optimum reduction of chronic disease risk in nonsmoking men and women." Thus, the multiple gram amounts of vitamin C taken by many healthy people may be superfluous.
The studies that ascertained approximately 120-200 mg daily of vitamin C is correct for prevention purposes in healthy people have typically not investigated whether people suffering from various diseases can benefit from larger amounts. In the case of the common cold , a review of published trials found that amounts of 2 grams per day in children appear to be more effective than 1 gram per day in adults, suggesting that large intakes of vitamin C may be more effective than smaller amounts, at least for this condition.5Ascorbyl palmitate, often sold as "vitamin C ester," is formed from ascorbic acid and palmitic acid creating a fat-soluble form of vitamin C that is sometimes used as an antioxidant food additive (E number E304). Oral supplements of ascorbyl palmitate are less effective, as it breaks down into its components before being digested.
Where to Find It
Citrus fruits, broccoli, red peppers, currants, Brussels sprouts, parsley, potatoes, and strawberries are good sources of vitamin C. Rose hips, harvested from rose bushes and sold as a supplement, are particularly high in vitamin C.
Although scurvy (severe vitamin C deficiency) is uncommon in Western societies, many doctors believe that most people consume less than optimal amounts. Fatigue, easy bruising , and bleeding gums are early signs of vitamin C deficiency that occur long before frank scurvy develops. Smokers have low levels of vitamin C and require a higher daily intake to maintain normal vitamin C levels. Women with preeclampsia have been found to have lower blood levels of vitamin C than women without the condition.6 Women who have lower blood levels of vitamin C have an increased risk of gallstones .7
People with kidney failure have an increased risk of vitamin C deficiency.8 However, people with kidney failure should take vitamin C only under the supervision of a doctor.
Best Form to Take
Vitamin C can be taken as ascorbic acid (a weak acid) or in buffered forms (such as sodium ascorbate, calcium ascorbate, or other mineral ascorbates). Buffered forms may be less likely to produce gastrointestinal distress, but they may be more likely to deliver excessive amounts of minerals.9
There is some limited evidence to suggest that vitamin C from natural sources (such as citrus extract) is more bioavailable than synthetic vitamin C, although natural vitamin C is more expensive. Therefore, it may make sense to take synthetic vitamin C and to obtain additional flavonoids and supporting nutrients from eating more fruits and vegetables.10
One trial found that Ester-C, a proprietary vitamin C product, was not more bioavailable than ascorbic acid.11
Fat-soluble forms of vitamin C (such as ascorbyl palmitate) are not to be preferred since vitamin C is naturally a water-soluble compound.12
Interactions with Supplements, Foods, & Other Compounds
Intake of large amounts of vitamin C can deplete the body of copper 13 , 14-an essential nutrient. People should be sure to maintain adequate copper intake at higher intakes of vitamin C. Copper is found in many multivitamin-mineral supplements. Vitamin C increases the absorption of iron and should be avoided by people with iron overload diseases (e.g., hemochromatosis, hemosiderosis). Vitamin C helps recycle the antioxidant , vitamin E .
Interactions with Medicines
Certain medicines interact with this supplement.
Types of interactions: Beneficial Adverse Check
Replenish Depleted Nutrients
Reduce Side Effects
Potential Negative Interaction
The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers' package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.
Caution: People with the following conditions should consult their doctor before supplementing with vitamin C: glucose-6-phosphate dehydrogenase deficiency, iron overload (hemosiderosis or hemochromatosis), history of kidney stones, or kidney failure.
Some people develop diarrhea after as little as a few grams of vitamin C per day, while others are not bothered by ten times this amount. Strong scientific evidence to define and defend an upper tolerable limit for vitamin C is not available. A review of the available research concluded that high intakes (2-4 grams per day) are well-tolerated by healthy people.15
It is widely (and mistakenly) believed that mothers who consume large amounts of vitamin C during pregnancy are at risk of giving birth to an infant with a higher-than-normal requirement for the vitamin. The concern is that the infant could suffer "rebound scurvy," a vitamin C deficiency caused by not having this increased need met. Even some medical textbooks have subscribed to this theory.16 In fact, however, the concept of "rebound scurvy" in infants is supported by extremely weak evidence.17 Since the publication in 1965 of the report upon which this mistaken notion is based, millions of women have consumed high amounts of vitamin C during pregnancy and not a single new case of rebound scurvy has been reported.18
A preliminary study found that people who took 500 mg per day of vitamin C supplements for one year had a greater increase in wall thickness of the carotid arteries (vessels in the neck that supply blood to the brain) than those who did not take vitamin C.19 Thickness of carotid artery walls is an indicator of progression of atherosclerosis . Currently, no evidence supports a cause-and-effect relationship for the outcome reported in this study. The vast preponderance of research suggests either a protective or therapeutic effect of vitamin C for heart disease , or no effect at all.
It has been suggested that people who form calcium oxalate kidney stones should avoid vitamin C supplements, because vitamin C can be converted into oxalate and increase urinary oxalate.20 , 21 Initially, these concerns were questioned because of potential errors in the laboratory measurement of oxalate.22 , 23 However, using newer methodology that rules out this problem, recent evidence shows that as little as 1 gram of vitamin C per day can increase the urinary oxalate levels in some people, even those without a history of kidney stones.24 , 25 In one case, 8 grams per day of vitamin C led to dramatic increases in urinary oxalate excretion and kidney stone crystal formation causing bloody urine.26 People with a history of kidney stones should consult a doctor before taking large amounts (1 gram or more per day) of supplemental vitamin C.
Despite possible therapeutic effects of vitamin C in people with diabetes at lower intakes, one case of increased blood sugar levels was reported after taking 4.5 grams per day.27
1. Balz F. Antioxidant Vitamins and Heart Disease. Presented at the 60th Annual Biology Colloquium, Oregon State University, February 25, 1999.
2. Levine M, Rumsey SC, Daruwala R, et al. Criteria and recommendations for vitamin C intake. JAMA 1999;281:1415-23.
3. Levine M, Conry-Cantilena C, Wang Y, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci 1996;93:3704-9.
4. Carr AC, Frei B. Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Am J Clin Nutr 1999;69:1086-107.
5. Hemilä H. Vitamin C supplementation and common cold symptoms: factors affecting the magnitude of the benefit. Med Hypotheses 1999;52:171-8.
6. Kharb S. Total free radical trapping antioxidant potential in pre-eclampsia. Int J Gynaecol Obstet 2000;69:23-6.
7. Simon JA, Hudes ES. Serum ascorbic acid and gallbladder disease prevalence among US adults. Arch Intern Med 2000;160:931-6.
8. Makoff R. Vitamin replacement therapy in renal failure patients. Miner Electrolyte Metab 1999;25:349-51 [review].
9. Gaby, AR. Nutritional Medicine. Concord, NH: Fritz Perlberg Publishing, 2011.
10. Gaby, AR. Nutritional Medicine. Concord, NH: Fritz Perlberg Publishing, 2011.
11. Gaby, AR. Nutritional Medicine. Concord, NH: Fritz Perlberg Publishing, 2011.
12. Gaby, AR. Nutritional Medicine. Concord, NH: Fritz Perlberg Publishing, 2011.
13. Sandstead HH. Copper bioavailability and requirements. Am J Clin Nutr 1982;35:809-14 [review].
14. Finley EB, Cerklewski FL. Influence of ascorbic acid supplementation on copper status in young adult men. Am J Clin Nutr 1983;37:553-6.
15. Johnston CS. Biomarkers for establishing a tolerable upper intake level for vitamin C. Nutr Rev 1999;57:71-7.
16. Wilson JD. Vitamin deficiency and excess. In Fauci AS, Braunwald E, Isselbacher KJ, et al. (eds). Harrison's Principles of Internal Medicine, 14th ed. New York, McGraw Hill, 1998, 487.
17. Cochrane WA. Overnutrition in prenatal and neonatal life: a problem? Can Med Assoc J 1965;93:893-9.
18. Gaby AR. The myth of rebound scurvy. Townsend Letter for Doctors 2000;June:122.
19. Dwyer J, Nicholson LM, Shircore A, et al. Vitamin C intake and progression of carotid atherosclerosis. The Los Angeles Atherosclerosis Study. American Heart Association Annual Meeting. March 2, 2000 [abstract].
20. Piesse JW. Nutritional factors in calcium containing kidney stones with particular emphasis on vitamin C. Int Clin Nutr Rev 1985;5:110-29 [review].
21. Ringsdorf WM, Cheraskin WM. Medical complications from ascorbic acid: a review and interpretation (part one). J Holistic Med 1984;6:49-63.
22. Hoffer A. Ascorbic acid and kidney stones. Can Med Assoc J 1985;32:320 [letter].
23. Wandzilak TR, D'Andre SD, Davis PA, Williams HE. Effect of high dose vitamin C on urinary oxalate levels. J Urol 1994;151:834-7.
24. Levine M. Vitamin C and optimal health. Presented at the February 25, 1999 60th Annual Biology Colloquium, Oregon State University, Corvallis, Oregon.
25. Levine M, Conry-Cantilena C, Wang Y, et al. Vitamin C pharmacokinetics in healthy volunteers: evidence for a recommended dietary allowance. Proc Natl Acad Sci 1996;93:3704-9.
26. Auer BL, Auer D, Rodgers AL. Relative hyperoxaluria, crystalluria and haematuria after megadose ingestion of vitamin C. Eur J Clin Invest 1998;28:695-700.
27. Branch DR. High-dose vitamin C supplementation increases plasma glucose. Diabetes Care1999;22:1218 [letter].
Last Review: 06-08-2015
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