Vitamin C

Also Known As
Ascorbic acid

Physiology and Clinical Effects
Vitamin C is a water-soluble vitamin that functions as a powerful antioxidant. Acting as an antioxidant, one of vitamin C’s important functions is to protect LDL cholesterol from oxidative damage. (Only when LDL is damaged, does cholesterol appear to lead to heart disease, and vitamin C may be the most important antioxidant protector of LDL.)1

Vitamin C is needed to make collagen, the “glue” that strengthens many parts of the body, such as muscles and blood vessels. Vitamin C also plays important roles in wound healing and as a natural antihistamine. This vitamin also aids in the formation of liver bile and helps to fight viruses and to detoxify alcohol and other substances.

Although vitamin C appears to have only a small effect in preventing the common cold, it reduces the duration and severity of a cold. Large amounts of vitamin C (e.g., 1–8 grams daily) taken at the onset of a cold episode shorten the duration of illness by an average of 23%.2

Recently, researchers have shown that vitamin C improves nitric oxide activity.3 Nitric oxide is needed for the dilation of blood vessels, potentially important in lowering blood pressure and preventing spasm of arteries in the heart that might otherwise lead to heart attacks. Vitamin C has reversed dysfunction of cells lining blood vessels.4 The normalization of the functioning of these cells may be linked to prevention of heart disease.

Evidence indicates that vitamin C levels in the eye decrease with age5 and that supplementing with vitamin C prevents this decrease,6 leading to a lower risk of developing cataracts.7 8 Healthy people have been reported to be more likely to take vitamin C and vitamin E supplements than those with cataracts in some,9 but not all, studies.10

Vitamin C has been reported to reduce activity of the enzyme aldose reductase in people.11 Aldose reductase is the enzyme responsible for accumulation of sorbitol in eyes, nerves, and kidneys of people with diabetes. This accumulation is believed to be responsible for deterioration of these parts of the body associated with diabetes. Therefore, interference with the activity of aldose reductase theoretically helps protect people with diabetes.

There is some speculative evidence that vitamin C might help prevent gallstones;12 however, supportive evidence remains preliminary.

Food Sources
Broccoli, red peppers, currants, Brussels sprouts, parsley, rose hips, acerola berries, citrus fruit, and strawberries are good sources of vitamin C.

Deficiency Risk and Symptoms
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.

Recommended Dosage
Doctors often recommend 500–1,000 mg per day. Most research uses levels that do not exceed 1,000 mg per day. However, even greater levels (up to 10,000 mg per day) are not uncommon. In terms of heart disease prevention, as little as 100–200 mg of vitamin C might be adequate.13

In contrast, current vitamin C researchers believe that 200 mg per day gets close to raising blood levels in healthy people about as high as they will go, and that supplementing more results in an excretion level almost identical to intake, meaning that more vitamin C does not stay in the body.14 This suggests that levels above 200 mg per day may prove to be superfluous for healthy people. The same kinds of studies that have ascertained that 200 mg is approximately correct for healthy people have not yet been done with sick individuals.

Contraindications
Some individuals develop diarrhea after as little as a few thousand milligrams of vitamin C per day, while others are not bothered by ten times this amount. However, high levels of vitamin C can deplete the body of copper15 16—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 probably increases the absorption of iron, although this effect is mild. Vitamin C helps recycle the antioxidant vitamin E.

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
• Kidney failure

It has been suggested that people who form kidney stones should avoid vitamin C supplements, because vitamin C can convert into oxalate and increase urinary oxalate.17 18 Initially, these concerns were questioned because the vitamin C converted to oxalate after urine had left the body.19 20 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.21 22 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.23 Until more is known, people with kidney stones or a history of stone formation should not take large amounts (1 gram per day) of supplemental vitamin C. Significantly lower amounts (100–200 mg per day) appear to be safe.

References:

1. Balz F. Antioxidant vitamins and heart disease. Presented at the 60th Annual Biology Colloquium, Oregon State University, Corvallis, Oregon, February 25, 1999.
2. Hemilδ H. Does vitamin C alleviate the symptoms of the common cold? A review of current evidence. Scand J Infect Dis 1994;26:1–6.
3. Taddei S, Virdis A, Ghaidoni L, et al. Vitamin C improves endotheoium-dependent vasodilation by restoring nitric oxide activity in essential hypertension. Circulation 1998;97:2222–9.
4. Chambers JC, McGregor A, Jean-Marie J, et al. Demonstration of rapid onset vascular endothelial dysfunction after hyperhomocysteinemia. An effect reversible with vitamin C therapy. Circulation 1999;99:1156–60.
5. Taylor A. Cataract: relationship between nutrition and oxidation. J Am Coll Nutr 1993;12:138–46 [review].
6. Taylor A, Jacques PF, Nadler D, et al. Relationship in humans between ascorbic acid consumption and levels of total and reduced ascorbic acid in lens, aqueous humor, and plasma. Curr Eye Res 1991;10:751–9.
7. Jacques PF, Chylack LT Jr. Epidemiologic evidence of a role for the antioxidant vitamins and carotenoids in cataract prevention. Am J Clin Nutr 1991;53:352S–55S.
8. Jacques PF, Chylack LT, McGandy RB, Hartz SC. Antioxidant status in persons with and without senile cataract. Arch Ophthalmol 1988;106:337–40.
9. Robertson JM, Donner AP, Trevithick JR. Vitamin E intake and risk of cataracts in humans. Ann NY Acad Sci 1989;570:372–82.
10. Seddon JM, Christen WG, Manson JE, et al. The use of vitamin supplements and the risk of cataract among US male physicians. Am J Public Health 1994;84:788–92.
11. Vincent TE, Mendiratta S, May JM. Inhibition of aldose reductase in human erythrocytes by vitamin C. Diabetes Res Clin Pract 1999;43:1–8.
12. Simon JA. Ascorbic acid and cholesterol gallstones. Med Hypotheses 1993;40:81–4.
13. Balz F. Antioxidant Vitamins and Heart Disease. Presented at the 60th Annual Biology Colloquium, Oregon State University, February 25, 1999.
14. 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 U S A 1996;93:3704–9.
15. Sandstead HH. Copper bioavailability and requirements. Am J Clin Nutr 1982;35:809–14 [review].
16. Finley EB, Cerklewski FL. Influence of ascorbic acid supplementation on copper status in young adult men. Am J Clin Nutr 1983;37:553–6.
17. Piesse JW. Nutritional factors in calcium containing kidney stones with particular emphasis on vitamin C. Int Clin Nutr Rev 1985;5(3):110–29 [review].
18. Ringsdorf WM, Cheraskin WM. Medical complications from ascorbic acid: a review and interpretation (part one). J Holistic Med 1984;6(1):49–63.
19. Hoffer A. Ascorbic acid and kidney stones. Can Med Assoc J 1985;32:320 [letter].
20. 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.
21. Levine M. Vitamin C and optimal health. Presented at the February 25, 1999 60th Annual Biology Colloquium, Oregon State University, Corvallis, Oregon.
22. 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 U S A 1996;93:3704–9.
23. 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.