Vitamin C is also known as ascorbic acid. It is a water-soluble vitamin that is necessary for normal growth and development. It is required for the growth and repair of tissues in all parts of your body. It is necessary to form collagen, an important protein used to make skin, scar tissue, tendons, ligaments, and blood vessels. Vitamin C is essential for the healing of wounds, and for the repair and maintenance of cartilage, bones, and teeth.
Vitamin C is one of many antioxidants. Vitamin E and beta-carotene are two other well-known antioxidants. Antioxidants are nutrients that block some of the damage caused by free radicals, which are by-products that result when our bodies transform food into energy. The build up of these by-products over time is largely responsible for the aging process and can contribute to the development of various health conditions such as cancer, heart disease, and a host of inflammatory conditions like arthritis. Antioxidants also help reduce the damage to the body caused by toxic chemicals and pollutants such as cigarette smoke.
Vitamin C deficiency can lead to dry and splitting hair; gingivitis (inflammation of the gums) and bleeding gums; rough, dry, scaly skin; decreased wound-healing rate, easy bruising; nosebleeds; weakened enamel of the teeth; swollen and painful joints; anemia; decreased ability to ward off infection; and, possibly, weight gain because of slowed metabolic rate and energy expenditure. A severe form of vitamin C deficiency is known as scurvy, which mainly affects older, malnourished adults.
The body does not manufacture vitamin C on its own, nor does it store it. It is therefore important to include plenty of vitamin C-containing foods in your daily diet.
All fruits and vegetables contain some amount of vitamin C. Foods that tend to be the highest sources of vitamin C include green peppers, citrus fruits and juices, strawberries, tomatoes, broccoli, turnip greens and other leafy greens, sweet and white potatoes, and cantaloupe.
Other excellent sources include papaya, mango, watermelon, brussels sprouts, cauliflower, cabbage, winter squash, red peppers, raspberries, blueberries, cranberries, and pineapples.
Vitamin C is water soluble and is regularly excreted by the body. Therefore, toxicity is very rare. Amounts greater than 2,000 mg/day, however, are not recommended because such high doses can lead to stomach upset and diarrhea.
Vitamin C is required for the synthesis of collagen, an important structural component of blood vessels, tendons, ligaments, and bone. Vitamin C also plays an important role in the synthesis of the neurotransmitter, norepinephrine. Neurotransmitters are critical to brain function and are known to affect mood. In addition, vitamin C is required for the synthesis of carnitine, a small molecule that is essential for the transport of fat to cellular organelles called mitochondria, for conversion to energy. Recent research also suggests that vitamin C is involved in the metabolism of cholesterol to bile acids, which may have implications for blood cholesterol levels and the incidence of gallstones.
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.
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.
Recent 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. However, in those women who did not take vitamin C supplements, dietary vitamin C intake was not significantly associated with CHD risk. This finding is inconsistent with data from numerous other prospective cohort studies that found inverse associations between dietary vitamin C intake or vitamin C plasma levels and CHD risk. Data from the National Institutes of Health (NIH) indicated that plasma and circulating cells in healthy, young subjects became fully saturated with vitamin C at a dose of 400 mg/day. The results of the NHANES I Epidemiologic Follow-up Study and the Nurses' Health Study suggest that maximum reduction of cardiovascular disease risk may require vitamin C intakes high enough to saturate plasma and circulating cells, and thus the vitamin C body pool.
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. In this population, serum levels of vitamin C were highly correlated with fruit and vegetable intakes. Therefore, as in many studies of vitamin C intake and cardiovascular disease risk, it is difficult to separate the effects of vitamin C on stroke risk from the effects of other components of fruits and vegetables, emphasizing the benefits of a diet rich in fruits and vegetables.
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. Because the possibility of bias is greater in case-control studies, prospective studies are generally given more weight in the evaluation of the effect of nutrient intake on disease. In general, prospective studies in which the lowest intake group consumed more than 86 mg of vitamin C daily have not found differences in cancer risk, while studies finding significant cancer risk reductions found them in people consuming at least 80 to 110 mg of vitamin C daily.
A prospective study of 870 men over a period of 25 years found that those who consumed more than 83 mg of vitamin C daily had a striking 64% reduction in lung cancer compared with those who consumed less than 63 mg per day. Although most large prospective studies found no association between breast cancer and vitamin C intake, two recent studies found dietary vitamin C intake to be inversely associated with breast cancer risk in certain subgroups. In the Nurses' Health Study, premenopausal women with a family history of breast cancer who consumed an average of 205 mg/day of vitamin C from foods had a 63% lower risk of breast cancer than those who consumed an average of 70 mg/day. In the Swedish Mammography Cohort, women who were overweight and consumed an average of 110 mg/day of vitamin C had a 39% lower risk of breast cancer compared to overweight women who consumed an average of 31 mg/day. A number of observational studies have found increased dietary vitamin C intake to be associated with decreased risk of stomach cancer, and laboratory experiments indicate that vitamin C inhibits the formation of carcinogenic compounds in the stomach. Infection with the bacteria, helicobacter pylori (H. pylori) is known to increase the risk of stomach cancer and also appears to lower the vitamin C content of stomach secretions. Although two intervention studies did not find a decrease in the occurrence of stomach cancer with vitamin C supplementation, more recent research suggests that vitamin C supplementation may be a useful addition to standard H. pylori eradication therapy in reducing the risk of gastric cancer.
Studies in the 1970's and 1980's conducted by Linus Pauling and colleagues suggested that very large doses of vitamin C (10 grams/day intravenously for 10 days followed by at least 10 grams/day orally indefinitely) were helpful in increasing the survival time and improving the quality of life of terminal cancer patients. However, two randomized placebo-controlled studies conducted at the Mayo clinic found no differences in outcome between terminal cancer patients receiving 10 grams of vitamin C/day orally or placebo. There were significant methodological differences between the Mayo Clinic and Pauling's studies, and recently, two researchers from the NIH suggested that the route of administration (intravenous versus oral) may have been the key to the discrepant results. Intravenous (IV) administration can result in much higher blood levels of vitamin C than oral administration, and levels that are toxic to certain types of cancer cells in culture can be achieved with intravenous but not oral administration of vitamin C. Thus, it appears reasonable to reevaluate the use of high-dose vitamin C as cancer therapy.
Currently, there are no results from controlled clinical trials indicating that vitamin C would adversely affect the survival of cancer patients. However, vitamin C should not be used in place of therapy that has been demonstrated effective in the treatment of a particular type of cancer, for example, chemotherapy or radiation therapy. If an individual with cancer chooses to take vitamin supplements, it is important that the clinician coordinating his or her treatment is aware of the type and dose of each supplement. While research is underway to determine whether combinations of antioxidant vitamins might be beneficial as an adjunct to conventional cancer therapy, definitive conclusions are not yet possible.
In a presentation at a meeting of the American Cancer Society, a scientist suggested that supplemental vitamin C might enhance the growth of cancer cells or protect them from cell-killing free radicals produced by radiation and some forms of chemotherapy. An article published in the Spring/Summer 2000 issue of the Linus Pauling Institute newsletter, Is vitamin C harmful for cancer patients?, provides additional insight on this topic.
Cataracts are a leading cause of visual impairment throughout the world. In the U.S., cataract-related expenditure is estimated to exceed 3 billion dollars annually. Cataracts occur more frequently and become more severe as people age. Decreased vitamin C levels in the lens of the eye have been associated with increased severity of cataracts in humans. Some, but not all, studies have observed increased dietary vitamin C intake and increased blood levels of vitamin C to be associated with decreased risk of cataracts. Those studies that have found a relationship suggest that vitamin C intake may have to be higher than 300 mg/day for a number of years before a protective effect can be detected. Recently, a 7-year controlled intervention trial of a daily antioxidant supplement containing 500 mg of vitamin C, 400 IU of vitamin E, and 15 mg of beta-carotene in 4,629 men and women found no difference between the antioxidant combination and a placebo on the development and progression of age-related cataracts. Therefore, the relationship between vitamin C intake and the development of cataracts requires further clarification before specific recommendations can be made.
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. Vitamin C supplement use was not associated with a significant increase in cardiovascular disease mortality in the cohort as a whole. Although a number of observational studies have found that higher dietary intakes of vitamin C are associated with lower cardiovascular disease risk, randomized controlled trials have not found antioxidant supplementation that included vitamin C to reduce the risk of cardiovascular disease in diabetic or other high-risk individuals.
It is possible that genetic differences may influence the effect of vitamin C supplementation on cardiovascular disease. When the results of one randomized controlled trial were reanalyzed based on haptoglobin genotype, antioxidant therapy (1000 mg/d vitamin C + 800 IU/d vitamin E) was associated with improvement of coronary atherosclerosis in diabetic women with two copies of the haptoglobin 1 gene but worsening of coronary atherosclerosis in those with two copies of the haptoglobin 2 gene. The significance of these findings is not entirely clear, but they suggest that there may be a subpopulation of people with diabetes who will benefit from antioxidant therapy while others may not benefit or could actually be harmed. Since randomized controlled trials have not found that supplementation with vitamin C is beneficial in preventing or treating heart disease in individuals with diabetes, individuals with diabetes should avoid consuming more than 250 mg/day from vitamin C supplements until more research is available. Since vitamin C intake from foods was not associated with increased mortality from cardiovascular disease, there is no reason to limit the intake of vitamin C-rich fruits and vegetables.
The work of Linus Pauling stimulated public interest in the use of large doses (greater than 1 gram/day) of vitamin C to prevent infection with the viruses responsible for the common cold. Reviews of the research conducted on this issue over the past 20 years conclude that, in general, large doses of vitamin C do not have a significant effect on the incidence of the common cold. However, a few studies have indicated that certain susceptible groups (e.g., individuals with low dietary intake and marathoners) may be less susceptible to the common cold when taking supplemental vitamin C. Additionally, large doses of vitamin C have been found to decrease the duration and severity of colds, an effect that may be related to the antihistamine effects found to occur with large doses (2 grams) of vitamin C.
Information from several studies, involving only small numbers of people, suggest that vitamin C (3 glasses of orange juice per day or up to 2000 mg per day as a supplement) may help decrease total and LDL cholesterol and triglycerides, as well as increase HDL levels (the good kind of cholesterol). Studies evaluating larger groups of people would be helpful in determining how accurate these preliminary research results are and to whom this potential benefit applies.
Free radicals, the damaging by-products of metabolism mentioned earlier, are associated with higher blood pressure in studies of animals and people. Population based studies (which involve observing large groups of people over time) suggest that people who eat foods rich in antioxidants, including vitamin C, are less prone to high blood pressure than people without these nutritious foods in their diet. For this reason, many clinicians recommend foods rich in vitamin C, particularly if you are at risk for high blood pressure. In fact, the diet most frequently recommended for treatment and prevention of hypertension, known as the DASH (Dietary Approaches to Stop Hypertension) diet advocates lots of fruits and vegetables, which are loaded with antioxidants.
1. Boothby LA, and Doering PL. Vitamin C and Vitamin E for Alzheimer's Disease. Ann Pharmacother. 2005 Dec;39(12):2073-9. Epub 2005 Oct 14.
Objective: To evaluate the literature on supplemental vitamin C and vitamin E therapy in the prevention and treatment of Alzheimer's disease (AD).
Data Sources: Literature retrieval was accessed through MEDLINE (1966-March 2005) using the key words antioxidants, vitamin C, vitamin E, Alzheimer's disease, and dementia. International Pharmaceutical Abstracts (1970-March 2005), Current Contents (1996-March 2005), Cochrane Database of Systematic Reviews (1994-March 2005), and Ebsco's Academic Search Elite (1975-March 2005) were searched with the same key words.
Study Selection and Data Extraction: Articles related to the objective that were identified through PubMed were included. DATA SYNTHESIS: Oral supplementation of vitamin C (ascorbic acid) and vitamin E (d-alfa-tocopherol acetate) alone and in combination have been shown to decrease oxidative DNA damage in animal studies in vivo, in vitro, and in situ. Recent results of a prospective observational study (n = 4740) suggest that the combined use of vitamin E 400 IU daily and vitamin C 500 mg daily for at least 3 years was associated with the reduction of AD prevalence (OR 0.22; 95% CI 0.05 to 0.60) and incidence (HR 0.36; 95% CI 0.09 to 0.99). Contradicting this is a previous prospective observational study (n = 980) evaluating the relationship between 4 years of vitamin C and E intake and the incidence of AD, which detected no difference in the incidence of AD during the 4-year follow-up. Recent meta-analysis results suggest that doses of vitamin E >/=400 IU daily for more than one year are associated with increased all-cause mortality. Mega-trial results suggest that vitamin E doses >/=400 IU daily for 6.9 years in patients with preexisting vascular disease or diabetes mellitus increase the incidence of heart failure, with no other outcome benefits noted.
Conclusions: In the absence of prospective, randomized, controlled clinical trials documenting benefits that outweigh recently documented morbidity and mortality risks, vitamin E supplements should not be recommended for primary or secondary prevention of AD. Although the risks of taking high doses of vitamin C are lower than those with vitamin E, the lack of consistent efficacy data for vitamin C in preventing or treating AD should discourage its routine use for this purpose.
2. Douglas RM, Chalker EB, Treacy B. Vitamin C for Preventing and Treating the Common Cold. Cochrane Database Syst Rev. 2000;(2):CD000980.
The role of oral ascorbic acid (vitamin C) in the prevention and treatment of colds remains controversial despite many controlled trials. There have also been a number of efforts to synthesize and/or overview the results of these trials, and controversy over what these overviews tell us. The objective of this review was to answer the following two questions: (1) Does regular high dosage supplementation with vitamin C reduce the incidence of colds? (2) Does taking vitamin C in high doses at the onset of a cold have a therapeutic effect? Randomised and non-randomised trials of vitamin C taken to prevent or treat the common cold.
Two reviewers independently extracted data and assessed trial quality. Thirty trials were included. The quality of the included trials was variable. Vitamin C in doses as high as one gram daily for several winter months, had no consistent beneficial effect on incidence of the common cold. For both preventive and therapeutic trials, there was a consistently beneficial but generally modest therapeutic effect on duration of cold symptoms. This effect was variable, ranging from -0.07% to a 39% reduction in symptom days.
The weighted difference across all of the studies revealed a reduction of a little less than half a symptom day per cold episode, representing an 8% to 9% reduction in symptom days. There was no clear indication of the relative benefits of different regimes or vitamin C doses. However in trials that tested vitamin C after cold symptoms occurred, there was some evidence that a large dose produced greater benefits than lower doses. Long term daily supplementation with vitamin C in large doses daily does not appear to prevent colds. There appears to be a modest benefit in reducing duration of cold symptoms from ingestion of relatively high doses of vitamin C. The relation of dose to therapeutic benefit needs further exploration.
3. Yilmaz C, Erdemli E, Selek H, Kinik H, Arikan M, Erdemli B. The Contribution of Vitamin C to Healing of Experimental Fractures. Arch Orthop Trauma Surg. 2001 Jul;121(7):426-8.
The benefits of various minerals and vitamins on fracture healing have been demonstrated in animal models. Vitamin C is an essential substance in fracture healing but has not been studied previously on an experimental basis. Sixteen rats were grouped randomly into control and vitamin C-supplemented groups. The right tibias of all rats were fractured by digital manipulation. One group received single high dose of vitamin C intramuscularly. On the 5th, 10th, 15th, and 20th days, two rats from each group were killed and the tibias examined under light microscopy. It was seen that the vitamin C-supplemented group went through the stages of fracture healing faster compared with the control group.
4. Naidu KA. Vitamin C in Human Health and Disease is Still a Mystery? An Overview. Nutr J. 2003 Aug 21;2:7.
Ascorbic acid is one of the important water soluble vitamins. It is essential for collagen, carnitine and neurotransmitters biosynthesis. Most plants and animals synthesize ascorbic acid for their own requirement. However, apes and humans can not synthesize ascorbic acid due to lack of an enzyme gulonolactone oxidase. Hence, ascorbic acid has to be supplemented mainly through fruits, vegetables and tablets. The current US recommended daily allowance (RDA) for ascorbic acid ranges between 100-120 mg/per day for adults. Many health benefits have been attributed to ascorbic acid such as antioxidant, anti-atherogenic, anti-carcinogenic, immunomodulator and prevents cold etc. However, lately the health benefits of ascorbic acid has been the subject of debate and controversies.
Danger of mega doses of ascorbic acid? Does ascorbic acid act as a antioxidant or pro-oxidant? Does ascorbic acid cause cancer or may interfere with cancer therapy? However, the Panel on dietary antioxidants and related compounds stated that the in vivo data do not clearly show a relationship between excess ascorbic acid intake and kidney stone formation, pro-oxidant effects, excess iron absorption. A number of clinical and epidemiological studies on anti-carcinogenic effects of ascorbic acid in humans did not show any conclusive beneficial effects on various types of cancer except gastric cancer. Recently, a few derivatives of ascorbic acid were tested on cancer cells, among them ascorbic acid esters showed promising anticancer activity compared to ascorbic acid. Ascorbyl stearate was found to inhibit proliferation of human cancer cells by interfering with cell cycle progression, induced apoptosis by modulation of signal transduction pathways. However, more mechanistic and human in vivo studies are needed to understand and elucidate the molecular mechanism underlying the anti-carcinogenic property of ascorbic acid. Thus, though ascorbic acid was discovered in 17th century, the exact role of this vitamin/nutraceutical in human biology and health is still a mystery in view of many beneficial claims and controversies.
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