VITAMIN C
Vitamin C is a water-soluble vitamin that is chemically unstable and highly sensitive to oxygen, light, heat, and air. Because of this instability, its potency can be reduced during food storage, processing, and cooking.
One of vitamin C’s primary roles is the maintenance of collagen, which is essential for healthy skin, connective tissue, blood vessels, and wound healing. Vitamin C is important for the healing of wounds and burns and plays a role in the formation of red blood cells. It supports immune function, helps the body respond to infections, and has antihistamine activity. Vitamin C also participates in amino acid metabolism, particularly phenylalanine and tyrosine, and helps convert inactive folic acid into its active form, folinic acid. In addition, vitamin C protects other vitamins from oxidation.
Vitamin C is absorbed through the mucous membranes of the mouth, stomach, and upper portion of the small intestine. Absorption efficiency decreases as the dose increases, which is why smaller doses taken throughout the day are often better absorbed than a single large dose.
Certain conditions increase the body’s need for vitamin C. These include physical or emotional stress, smoking, high fever, prolonged antibiotic use, exposure to chemical fumes or pesticides, aspirin and other pain relievers, steroid medications, and oral contraceptives. Copper acts as a functional antagonist to vitamin C.
Vitamin C is generally considered safe, even at relatively high doses. However, some individuals may experience side effects such as loose stools, intestinal gas, mild skin rashes, or a burning sensation during urination. Large doses may pose a risk for individuals prone to kidney stones, and rare genetic conditions can predispose certain people to stone formation when high doses are consumed.
The disease associated with severe vitamin C deficiency is scurvy. Early symptoms include fatigue, weakness, irritability, weight loss, and vague muscle and joint pain. As deficiency progresses, connective tissue becomes fragile. Splinter hemorrhages may appear near the ends of the fingernails, wounds heal poorly, old scars may break down, and spontaneous bleeding can occur. Teeth may loosen, particularly around existing dental roots. Advanced deficiency can lead to secondary infection, gangrene, and widespread hemorrhage.
Additional signs of scurvy may include conjunctival hemorrhage, nerve compression from internal bleeding, swelling of the lower extremities, reduced urine output, impaired blood vessel reactivity, and arthritis-like symptoms. Bleeding gums, while commonly associated with scurvy, are not its most distinctive feature. A hyperkeratotic hair follicle surrounded by redness or hemorrhage is considered nearly diagnostic.
Vitamin C has been shown in laboratory research to stimulate interferon production and exhibit antiviral activity against a variety of viruses. It has been used to counteract gastrointestinal bleeding associated with aspirin or alcohol use and to inhibit the formation of carcinogenic nitrosamines from dietary nitrates and nitrites. Some research suggests a supportive role in recovery following heart attacks.
Epidemiological research published in the early 1990s [see below] reported an association between higher vitamin C intake and reduced cancer risk, particularly for non–hormone-dependent cancers. A majority of studies reviewed at that time found protective effects associated with dietary vitamin C and fruit consumption.
At a national symposium on vitamin C held in 1990 [see below], researchers concluded that vitamin C has broad biological effects, many related to its chemical properties rather than its classical vitamin function. Vitamin C was identified as a powerful free-radical scavenger, capable of protecting immune cell function and inhibiting chemically induced cellular transformation. Animal studies demonstrated delayed tumor development and radioprotective effects. Vitamin C was also shown to stimulate alkaline phosphatase activity, which is important for bone mineralization.
Vitamin C works in close partnership with other antioxidants. It helps regenerate oxidized vitamin E back to its active form and is itself regenerated through glutathione, a process that requires selenium. Adequate vitamin C supports red blood cell glutathione levels and overall antioxidant defense.
Large observational studies have associated higher vitamin C intake with reduced cardiovascular disease risk and lower overall mortality. Vitamin C has also been linked to reduced risk of cataract formation, possibly due to its presence in the lens of the eye alongside antioxidant enzymes such as glutathione peroxidase, catalase, and superoxide dismutase.
Research from national nutrition surveys has shown a positive relationship between dietary vitamin C intake and pulmonary function, measured by forced expiratory volume (FEV₁). This association was observed in both smokers and non-smokers and appeared particularly beneficial for individuals with asthma or chronic bronchitis. These effects are thought to be related to vitamin C’s antioxidant and immune-supporting properties, including reduced airway responsiveness and protection against exercise-induced bronchospasm [see below].
AMERICAN JOURNAL OF CLINICAL NUTRITION, 1991;53: 2701-282s “Vitamin C and Cancer Prevention: The Epidemiological Evidence:, The protective effect of vitamin C for nonhormone dependent cancers is strong. 33 out of 46 studies evaluating dietary vitamin C have shown significant protection. 21 of 29 studies found fruit intake to be protective as well.
According to the symposium held by the National Cancer Institutes of Health in 1990: Vitamin C has multiple complex biological effects, probably more widespread than any other nutrient. Some of the effects relate to vitamin C’s chemical properties and not from its role as a vitamin. Vitamin C’s interaction with enzymes is important. Studies were reported on its effect as a free radical scavenger. Vitamin C was the most effective of all free radical scavengers tested. Vitamin C deficiency was shown to reduce leukocyte morphology and reduce its chemotactic response. Vitamin C has been shown to suppress chemically induced transformation of cancer cells. It has also been shown that ascorbate prevents oncogenic transformation of cells infected with certain viruses such as the mouse sarcoma virus. The development of mammary tumors in animal models has been delayed in ascorbate treated animals. The radioprotective effects of ascorbic acid were also shown in animal models. Ascorbate stimulates alkaline phosphatase activity which is necessary for mineralization.
Archives Family Medicine September 1994, 3:809-820 “The Merging Role of Vitamins as Antioxidants” Oxidation may be involved in atherosclerosis by altering LDL to where it may effect the endothelium and start the athersclerotic process. LDL can carry molecules of vitamin E, beta-carotene and CoQ10 which may conteract or delay lipid peroxidation. High level vitamin E supplementation decreases LDL susceptibility to oxidation in vitro. Vitamin C helps regenerate oxidized vitamin E back to its reduced or antioxidant state. Vitamin C is regenerated via glutathione, using selenium as a cofactor. Vitamin C supplementation can help maintain red blood cell glutathione. In a cohort study of 11,000 people there was a significant reduction in cardiovascular disease and total death in individuals who had higher intakes of vitamin C. In an 8 year follow-up of the 80,000 women in the Nurses Health Study the top 5th of the cohort with the resp to vitamin E intake averaging 200 IU/day had a relative risk of major coronary artery disease of .66. There is an association between supplementary ascorbic acid and vitamin E intake over the previous 5 years and the decreased risk for senile cataracts of 2 1/2 times; with regards to cataract formation, glutathione and vitamin C are present in the lens of the eye as the antioxidant enzymes glutathione peroxidase, catalase and superoxide dismutase. Individuals consuming more than 300mg/d of C or 400 IU of E have about 1/3 the risk of developing cataracts. Vitamin C has also been associated with the decreased risk of many gastrointestinal cancers.
American Journal of Clinical Nutrition 1994; 59; 110-4″Relationship Between Dietary Vitamin C Intake and Pulmonary function in the First National Health and Nutrition Examination Survey” This study evaluated vitamin C intake and pulmonary function utilizing expiratory volume in 1 second (FEV1) in 2,526 adults between 1971 and 1974. After adjusting for variables, dietary vitamin C intake was positively and significantly associated with the level of FEV1. The authors conclude that vitamin C has a protective effect on pulmonary function. This beneficial effect was not restricted to just smokers. Vitamin C intake appears to have more benefit in asthmatic and bronchitis patients. The beneficial effect may be due to vitamin C’s antioxidant capabilities. It appears to improve immune function, decrease the responsiveness of airways and protect against exercise induced bronchospasm in asthmatic subjects who are taking vitamin C.
