Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble vitamin. Unlike most mammals, humans do not have the ability to make their own vitamin C. Therefore, we must obtain vitamin C through our diet.

Vitamin C is also a highly effective antioxidant. Even in small amounts vitamin C can protect indispensable molecules in the body, such as proteins, lipids (fats), carbohydrates, and nucleic acids (DNA and RNA) from damage by free radicals and reactive oxygen species that can be generated during normal metabolism as well as through exposure to toxins and pollutants (e.g. smoking). Vitamin C may also be able to regenerate other antioxidants such as vitamin E

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Deficiency

Scurvy

Severe vitamin C deficiency has been known for many centuries as the potentially fatal disease,

scurvy

. By the late 1700's the British navy was aware that scurvy could be cured by eating oranges or lemons, even though vitamin C would not be isolated until the early 1930's. Symptoms of scurvy include bleeding and bruising easily, hair and tooth loss, joint pain and swelling. Such symptoms appear to be related to the weakening of blood vessels, connective tissue, and bone, which contain collagen.

The Recommended Dietary Allowance (RDA)

 Disease Prevention

Coronary Heart Disease

Until recently, the results of most prospective studies indicated that low or deficient intakes of vitamin C were associated with an increased risk of cardiovascular diseases and that modest dietary intakes of about 100 mg/day were sufficient for maximum reduction of cardiovascular disease risk among nonsmoking men and women. In addition, several studies had failed to find significant reductions in the risk of coronary heart disease (CHD) among vitamin C supplement users in well-nourished populations. One notable exception was the First National Health and Nutrition Examination Study (NHANES I) Epidemiologic Follow-up Study. This study found that the risk of death from cardiovascular diseases was 42% lower in men and 25% lower in women who consumed more than 50 mg/day of dietary vitamin C and who regularly took vitamin C supplements, corresponding to a total vitamin C intake of about 300 mg/day . Results from the Nurses’ Health Study, based on the follow-up of more than 85,000 women over 16 years, also suggest that higher vitamin C intakes may be cardioprotective. In this study, vitamin C intakes of more than 359 mg/day from diet plus supplements or supplement use itself were associated with a 27-28% reduction in CHD risk.

Stroke

With respect to vitamin C and cerebrovascular disease, a prospective study that followed more than 2,000 residents of a rural Japanese community for 20 years found that the risk of stroke in those with the highest serum levels of vitamin C was 29% lower than in those with the lowest serum levels of vitamin C . Additionally, the risk of stroke in those who consumed vegetables 6-7 days of the week was 54% lower than in those who consumed vegetables 0-2 days of the week.

Cancer A large number of studies have shown that increased consumption of fresh fruits and vegetables is associated with a reduced risk for most types of cancer. Such studies are the basis for dietary guidelines endorsed by the U.S. Department of Agriculture and the National Cancer Institute, which recommend at least 5 servings of fruits and vegetables per day. A number of case-control studies have investigated the role of vitamin C in cancer prevention.  Most have shown that higher intakes of vitamin C are associated with decreased incidence of cancers of the mouth, throat and vocal chords, esophagus, stomach, colon-rectum, and lung.

Disease Treatment

Cardiovascular Disease

Vasodilation

The ability of blood vessels to relax or dilate is compromised in individuals with atherosclerosis.  The damage to the heart muscle caused by a heart attack and damage to the brain caused by a stroke is related, in part, to the inability of blood vessels to dilate enough to allow blood flow to the affected areas.  The pain of angina pectoris is also related to insufficient dilation of the coronary arteries.  Treatment with vitamin C has consistently resulted in improved dilation of blood vessels in individuals with atherosclerosis as well as those with angina pectoris, congestive heart failure, high cholesterol, and high blood pressure.  Improved blood vessel dilation has been demonstrated at a dose of 500 mg of vitamin C daily

Hypertension Individuals with high blood pressure (hypertension) are at increased risk of developing cardiovascular diseases.  Several studies have demonstrated a blood pressure lowering effect of vitamin C supplementation. One recent study of individuals with high blood pressure found that a daily supplement of 500 mg of vitamin C resulted in an average drop in systolic blood pressure of 9% after 4 weeks.

Diabetes Mellitus Cardiovascular diseases (heart disease and stroke) are the leading cause of death in individuals with diabetes. Evidence that diabetes is a condition of increased oxidative stress led to the hypothesis that higher intakes of antioxidant nutrients could help decrease cardiovascular disease risk in diabetic individuals. In support of this hypothesis, a 16-year study of 85,000 women, 2% of whom were diabetic, found that vitamin C supplement use (400 mg/day or more) was associated with significant reductions in the risk of fatal and nonfatal coronary heart disease in the entire cohort as well as those with diabetes. In contrast, a 15-year study of postmenopausal women found that diabetic women who reported taking at least 300 mg/day of vitamin C from supplements when the study began were at significantly higher risk of death from coronary heart disease and stroke than those who did not take vitamin C supplements

Common cold The work of Linus Pauling stimulated public interest in the use of large doses (greater than 1 g/day) of vitamin C to prevent the common cold. In the past 30 years, numerous placebo-controlled trials have examined the effect of vitamin C supplementation on the prevention and treatment of colds. A meta-analysis of 30 placebo-controlled prevention trials found that vitamin C supplementation in doses up to 2 g/day did not decrease the incidence of colds.

However, in a subgroup of marathon runners, skiers and soldiers training in the Arctic, doses ranging from 250 mg/day to 1 g/day decreased the incidence of colds by 50%. Overall, the preventive use of vitamin C supplementation reduced the duration of colds by about 8% in adults and 14% in children. Most of the prevention trials used a dose of 1 g/day.

Supplements

Vitamin C (L-ascorbic acid) is available in many forms, but there is little scientific evidence that any one form is better absorbed or more effective than another.

Natural vs. synthetic vitamin C

Natural and synthetic L-ascorbic acid are chemically identical and there are no known differences in their biological activities or bioavailability .

Mineral ascorbates

Mineral salts of ascorbic acid are buffered and therefore, less acidic than ascorbic acid. Some people find them less irritating to the gastrointestinal tract than ascorbic acid. Sodium ascorbate and calcium ascorbate are the most common forms, although a number of other mineral ascorbates are available. Sodium ascorbate generally provides 131 mg of sodium per 1,000 mg of ascorbic acid, and pure calcium ascorbate provides 114 mg of calcium per 1,000 mg of ascorbic acid.

Vitamin C with bioflavonoids

Bioflavonoids are a class of water-soluble plant pigments that are often found in vitamin C-rich fruits and vegetables, especially citrus fruits. Although many bioflavonoids are thought to function as antioxidants, there is little evidence that the bioflavonoids in most commercial preparations increase the bioavailability or efficacy of vitamin C.

Ascorbate and vitamin C metabolites

One such supplement (Ester-C^®) contains mainly calcium ascorbate, but also contains small amounts of the vitamin C metabolites dehydroascorbate (oxidized ascorbic acid), calcium threonate, and trace levels of xylonate and lyxonate. Although the metabolites are supposed to increase the bioavailability of vitamin C, the only published study in humans found no difference between Ester-C^® and commercially available ascorbic acid tablets with respect to the absorption and urinary excretion of vitamin C. Ester-C^® should not be confused with ascorbyl palmitate, which is also marketed as "vitamin C ester" (see below).