Vitamin C

 

Vitamin C Clinical Report Summary

 

Vitamin C is used for increasing the healing rate of wounds, burns, fractures, ulcers, and pressure sores, and is commonly recommended for cancer, the common cold, broken capillaries, and those who easily bruise.  It is also used to prevent and treat scurvy, and increase iron absorption from the gastrointestinal tract.  The current clinical research provides some promising benefits of vitamin C supplementation, particularly in areas of the common cold and cancer.  A randomized, controlled 5-year trial suggests that vitamin C supplementation significantly reduces the frequency of the common cold but had no apparent effect on the duration or severity of the common cold (1).  In another study evaluating the effect of vitamin C on the common cold during winter months, 168 patients were given either vitamin C or a placebo.  Compared with the placebo group, researchers observed the vitamin C group had 26% fewer colds, fewer virally-challenged days (85 vs. 178), and a 42% shorter duration of severe symptoms (2). Additionally, a subset of studies observed that vitamin C supplementation benefited persons living in extreme conditions such as soldiers in sub-artic exercises, skiers, and marathon runners.  Researchers reported results suggested vitamin C supplementation reduced the risk of developing a cold by approximately 50%.  Scientists evaluated epidemiologic evidence of a protective effect of vitamin C intake and cancers, and found that protection for non-hormone-dependent cancers is strong (3, 4). Of the 46 such studies in which a dietary vitamin C index was calculated, 33 found statistically significant protection against cancers, with high intake conferring approximately a twofold protective effect compared with low intake (3). 

 

Vitamin C Overview

 

Vitamin C is an essential water-soluble vitamin required to form collagen in bones, cartilage, muscle, and the capillary and blood vessels.  As an ascorbic acid, vitamin C is arguably the most important water-soluble biological antioxidant because of its ability to scavenge reactive oxygen species and reactive nitrogen species, which cause cellular injury.  Vitamin C also works synergistically with iron to improve absorption and bioavailability of the mineral.  Foods rich in vitamin C include: peppers, citrus fruits and juices, brussel sprouts, cauliflower, cabbage, kale, collards, mustard greens, broccoli, spinach and strawberries (5, 6).  It should be noted that cooking can destroy vitamin C activity.

 

Safe Use of Vitamin C

 

The RDI ranges from 75-120 mg per day, with an additional 35 mg recommended for active smokers.  Dietary supplements typically range from 500-2000 mg.  Higher intakes are considered safe because vitamin C is water soluble and easily excreted, however diarrhea is a common side effect of excess vitamin C intake.  It should be noted that ascorbic acid available in chewable tablets can be harmful to teeth enamel if chewed frequently.

 

Clinical Studies for Vitamin C

 

1. Vitamin C, the Common Cold and Immune Support

 

Effect of vitamin C on common cold: randomized controlled trial. Sasazuki, S., Sasaki, S., Tsubono, Y., Okubo, S., Hayashi, M., Tsugane, S. 

OBJECTIVE: To investigate the relationship between the common cold and vitamin C supplementation. DESIGN: A double-blind, 5-year randomized controlled trial. SETTING: A village in Akita prefecture, one of the regions in Japan with the highest mortality from gastric cancer. SUBJECTS: Participants in annual screening programs for circulatory diseases conducted under the National Health and Welfare Services Law for the Aged, and diagnosed as having atrophic gastritis. Of the 439 eligible subjects, 144 and 161 were assigned to receive 50 or 500 mg of vitamin C, respectively, after protocol amendment. During the supplementation phase, 61 dropped out, and 244 completed the trial. Intervention: Daily vitamin C supplementation of 50 mg (low-dose group) or 500 mg (high-dose group). RESULTS: Total number of common colds (per 1000 person-months) was 21.3 and 17.1 for the low- and high-dose groups, respectively. After adjustment for several factors, the relative risks (95% confidence interval (CI)) of suffering from a common cold three or more times during the survey period was 0.34 (0.12-0.97) for the high-dose group. No apparent reduction was seen for the severity and duration of the common cold. CONCLUSION: A randomized, controlled 5-year trial suggests that vitamin C supplementation significantly reduces the frequency of the common cold but had no apparent effect on the duration or severity of the common cold. However, considering several limitations due to protocol amendment, the findings should be interpreted with caution.

 

Preventing the common cold with a vitamin C supplement: a double-blind, placebo-controlled survey.  Van Straten, M., Josling, P.

One hundred sixty-eight volunteers were randomized to receive a placebo or a vitamin C supplement, two tablets daily, over a 60-day period between November and February. They used a five-point scale to assess their health and recorded any common cold infections and symptoms in a daily diary. Compared with the placebo group, the active-treatment group had significantly fewer colds (37 vs 50, P less than .05), fewer days challenged virally (85 vs 178), and a significantly shorter duration of severe symptoms (1.8 vs 3.1 days, P less than .03). Consequently, volunteers in the active group were less likely to get a cold and recovered faster if infected. Few side effects occurred with the active treatment, and volunteers reported greatly increased satisfaction with the study supplement compared with any previous form of vitamin C. This well-tolerated vitamin C supplement may prevent the common cold and shorten the duration of symptoms. Volunteers were generally impressed by the protection afforded them during the winter months and the general acceptability of the study medication.

 

2. Vitamin C and Cancer Protection

 

Epidemiologic evidence for vitamin C and vitamin E in cancer prevention.  Byers T, Guerrero N.

Antioxidant nutrients have been hypothesized to be protective against cancer. Vitamin C is a major circulating water-soluble antioxidant, and vitamin E is a major lipid-soluble antioxidant. Many case-control and cohort studies have related cancer risk to estimates of nutrient intake derived from food intake reports. Diets high in fruit and vegetables, and hence high in vitamin C, have been found to be associated with lower risk for cancers of the oral cavity, esophagus, stomach, colon, and lung. Diets high in added vegetable oils, and hence high in vitamin E, have been less consistently shown to be associated with cancer protection. This may be because vitamin E offers less protection against cancer or because the estimation of vitamin E intake is less accurate than is the estimation of vitamin C intake. In contrast with the findings from epidemiologic studies based on foods, observational studies of nutrients consumed in supplements and recent experimental trials provide little support for a strong protective role for vitamins C or E against cancer. If vitamins C or E are indeed protective against cancer, that protection may derive from their consumption in complex mixtures with other nutrients and with other bioactive compounds as found in the matrix provided by whole foods.

 

Vitamin C References

 

1. Sasazuki, S., Sasaki, S., Tsubono, Y., Okubo, S., Hayashi, M., Tsugane, S.  Effect of vitamin C on common cold: randomized controlled trial. Eur J Clin Nutr. 2006 Jan;60(1):9-17.
2. Van Straten, M., Josling, P. Preventing the common cold with a vitamin C supplement: a double-blind, placebo-controlled survey. Adv Ther. 2002 May-Jun;19(3):151-159.
3. Block, G. Vitamin C and cancer prevention: the epidemiologic evidence. Am J Clin Nutr. 1993 Apr;57(4):598-599.
4. Byers T, Guerrero N. Epidemiologic evidence for vitamin C and vitamin E in cancer prevention. Am J Clin Nutr 1995;62:1385S-92S.
5. Pennington, J.A.T. Bowes & Church's Food Values of Portions Commonly Used. 1994. J.B. Lippincott Company, Philadelphia.
6. "Vitamin C." PDR Health.com. Accessed: Sept. 27, 2000. < http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/vit_0264.shtml>.