Vitamin C is a water-soluble vitamin that promotes wound healing and healthy blood vessels, joints, gums and connective tissue. Vitamin C helps in the synthesis of COLLAGEN, a structural protein that provides strength to bones and tissues. Most animals make ample vitamin C; exceptions include guinea pigs, humans and other primates, and certain bats.
Vitamin C occurs in high levels in endocrine (hormonesecreting) glands. It is needed by the ADRENAL GLANDS to make hormones: EPINEPHRINE (adrenaline), a stress hormone, plus the steroids regulating BLOOD SUGAR and the hormones regulating blood minerals, and assists in the activation of other hormones. Vitamin C also occurs in high levels in the brain, and it plays a role in nerve transmission through the production of SEROTONIN and norepinephrine, brain chemicals called NEUROTRANSMITTERS. Neurotransmitters are chemicals synthesized by nerve cells to conduct impulses between cells. Vitamin C is involved in the metabolism of folic acid.
Vitamin C serves as a powerful antioxidant and helps to prevent oxidative damage in the body. It can block many types of highly reactive chemical species called FREE RADICALS, including superoxide and hydroxyl radicals in blood and body fluids, as well as regenerating VITAMIN E, the free radical scavenger of cell membranes and lipids. As a versatile antioxidant, vitamin C offers protection against airborne pollutants and supports drug detoxification by the liver. Dietary vitamin C can increase the absorption of heme iron (the form in meat) two- to fourfold. Vitamin C suppresses the formation of NITROSOAMINES and quinones, known to cause cancer (carcinogens). On the other hand, it is possible that vitamin C can p3?330F”2cipate in the BHA-induced tissue growth in the stomach of rats, thus enhancing carcinogenesis. However, a higher consumption of vitamin C contributes to higher plasma levels of other antioxidants, including vitamin E.
Possible Role of Vitamin C in Disease
The functions of vitamin C in the body and the amounts required for optimal health remain one of the most controversial areas in nutrition. The following topics have been the focus of recent research.
Scurvy: This full-blown vitamin C deficiency disease is characterized by swollen joints, poor wound healing, muscle wasting, bleeding gums and susceptibility to infection. In scurvy, defective COLLAGEN is formed, leading to diseased connective tissue. (Sounds a lot like Primary Fibromyalgia Syndrome). Vitamin C is required to synthesize collagen building blocks, hydroxylysine and hydroxyproline, for normal collagen formation. Scurvy has largely been eradicated from industrialized nations, though it continues to affect certain populations: the elderly, alcoholics and chronically ill people. When large amounts of vitamin C are consumed, the body adapts by accelerating excretion and metabolism. When consumption suddenly drops, a person may experience a short-term vitamin C deficiency until the body readapts (“rebound scurvy”). Infants born to mothers who have taken large amounts of vitamin C may experience rebound scurvy after birth unless they are supplemented.
Infection and colds: Whether vitamin C can cure the common cold has remained a controversial issue since Dr. Linus Pauling first suggested it in 1970. The research that has been conducted since that time has yielded mixed results, possibly reflecting flaws in experiment design. There is general agreement that vitamin C can decrease the duration and severity of colds. The vitamin can affect the outcome by blocking viruses, as well as by helping the IMMUNE SYSTEM. White cells that devour bacteria and abnormal cells require vitamin C for normal functioning; vitamin C levels decline in these cells during infection and exposure to drugs, medications, alcohol and cigarette smoking.
Cancer: A variety of population studies suggest that a low vitamin C intake correlates with a higher rate of CANCER and that vitamin C has a protective effect for cancer of the oral cavity, larynx, esophagus and stomach. Data supporting a beneficial relationship between vitamin C and bladder, cervix, endometrium and breast cancer are not as convincing, though suggestive. Vitamin C supplementation reduces the rate of precancerous changes in the stomach. It protects against cervical dysplasia, a predisposing condition to cervical cancer, and it inhibits human leukemia cells in culture. Vitamin C can block the formation of cancer-causing agents like NITROSOAMINES, and it is a powerful blocker of free radicals, which can be carcinogenic. Whether vitamin C does more than prevent certain cancers, and whether it can extend the lives of terminally ill cancer patients, remains controversial. More research is needed to resolve these issues.
Cardiovascular disease: A popular hypothesis for the origin of atherosclerosis (cholesterol clogged arteries) states that the oxidation of LDL promotes the disease process. SEE: LINUS PAULING’S UNIFIED THEORY ON ATHEROSCLEROSIS. Vitamin C may help prevent oxidative damage to LDL (LOWDENSITY LIPOPROTEINS), lipid-transport particles implicated in clogging arteries. Vitamin C can increase HDL, the beneficial form of cholesterol, and it may lower total cholesterol values. However, epidemiological studies did not detect a correlation between vitamin C intake and the risk of cardiovascular disease, and there as yet have not been randomized clinical studies of vitamin C in reducing cardiovascular risk. Population studies have found an increased risk of elevated blood pressure with low vitamin C intake or low vitamin C plasma levels; however, studies of treatment of hypertension with vitamin C have not been conclusive. Mortality from all causes of death was strongly inversely related to vitamin C intake, but other studies of vitamin C in preventing cardiovascular disease have yielded negative results. Additional research is justified.
Aging: Free radical damage is implicated in aging, which can be viewed as the result of accumulated damaged protein and DNA and of damaged repair mechanisms. Population studies suggest that the consumption of ample fruits and vegetables, including those that are rich sources of vitamin C, decrease the risks of degenerative diseases associated with aging. Of the multitude of beneficial substances in these foods with antioxidant activity, vitamin C appears likely to play a central role.
Allergies: Vitamin C can help reduce asthma in certain asthmatics, and it may reduce the severity of allergy symptoms by alleviating stuffy sinuses, achy joints and puffy eyes. Vitamin C helps detoxify HISTAMINE, which promotes these inflammation symptoms.
Cataracts: Free radicals probably promote cataracts and macular degeneration with aging. Thus animals fed vitamin E-deficient diets develop macular degeneration and people with low-levels of antioxidants in their blood have a higher risk of cataracts. Adequate vitamin C, carotenoids and vitamin E consumption are related to a decreased risk of cataracts associated with aging. Several studies have suggested that antioxidant supplements, including vitamin C, decrease the risk of cataract formation. Vitamin C supplementation may halt or retard cataract development.
Other conditions: A variety of studies suggest that supplements of vitamin C can: decrease the risk Of PERIODONTAL DISEASE, help diabetics maintain healthy gums; help overcome infertility in male smokers; and ease muscle soreness in athletes.
Sources
Fresh vegetables and fresh food are the best sources of vita-min C, including CITRUS FRUIT, CANTALOUPE, green PEPPERS, BROCCOLI, PAPAYA, berries and green leafy vegetables. Grains lack vitamin C. Vitamin C is the most unstable vitamin: In food it is destroyed by heat and by exposure to air and cooking and processing of foods leads to extensive destruction. Microwave cooking minimizes losses. Destruction in fruit and vegetables is faster at room temperature than in the refrigerator, and is fastest if the vegetable is chopped or peeled. Ascorbic acid powder is stable indefinitely if kept dry.
Requirements
Currently, the RECOMMENDED DIETARY ALLOWANCE (RDA) for vitamin C is 60 mg for non-smokers and 100 mg for smokers. Many nutritional scientists believe this is too little for optimal health, though fewer advocate consuming as much as 2 to 10 g daily. Nonetheless there is substantial agreement that from 200 to 1,000 mg daily can provide insurance for a diet com-promised by processed food. The level actually needed to sat-urate tissues has recently been studied. Data published in 1996 indicate that RDA for adults should be 200 mg. Steady state plasma and tissue concentrations of vitamin C were measured at varying doses in healthy volunteers, after first being depleted with a vitamin C-deficient diet. Bioavailability was maximal at 200 mg of vitamin C per day; higher levels of vitamin C did not appreciably change tissue saturation. Vitamin C needs are highly individualistic and exposure to pollutants, drugs, medications, smoking, infections, recovery from injury or surgery, high stress levels and heavy drinking often increases the need for vitamin C above the usual intake. The elderly or people who rely on medications like aspirin, barbiturates, L-dopa, phenacetin and cortisone need more vitamin C.
Safety
Vitamin C may have a dark side. Vitamin C increases iron uptake and hypothetically this could lead to iron accumulation in those with an inherited tendency to store iron. That is, unless the Iron is water-soluble. (See Iron in the Mineral Section). Iron and vitamin C spontaneously form free radicals (prooxidant effect). Excessive vitamin C supplementation together with excessive iron storage may be detrimental. However, under usual physiologic conditions, the amount of free iron would likely be very small; it would be stored in the iron binding protein FERRITIN. With injury or inflammation some iron could be released and could react with hydrogen peroxide to produce damaging free radicals. In susceptible people large amounts of vitamin C could promote the appearance of oxalate in the urine, thus increasing the risk of kidney stones. Supplementing with magnesium and extra vitamin B6 can diminish this risk.
Side effects of excessive vitamin C supplements include diarrhea and cramps, and over time this could promote MALABSORPTION. If diarrhea and upset stomach occurs cut back on the dose. Chewable vitamin C can erode tooth enamel, and taking aspirin with vitamin C can aggravate gastric bleeding caused by aspirin. Extremely high intakes of vitamin C may increase the need for COPPER, and may increase the risk of GOUT in individuals who are genetically susceptible to those conditions. If you are prone to gout or kidney stones, or if you are pregnant, do not supplement with vitamin C without first consulting your physician.
NOTE: WE USE MIXED ASCORBATES IN OUR OFFICE. THIS A “BUFFERED” FORM OF VITAMIN C AND REDUCES MOST BOWEL INTOLERANCES.
Vitamin C interferes with the effectiveness of amphetamines, blood thinning drugs, and tricyclic antidepressants like Elavil, and it can alter lab tests like urinary glucose and occult blood for bowel cancer. NOTE: Inform your physician if you are taking vitamin C or any other supplements before having diagnostic laboratory tests. Taper off gradually when you stop supplementation of 500 mg or more to avoid possible short-term scurvy-like symptoms and temporary lowered resistance to infections.
J Am Coll Nutr 1998 Aug; 17(4): 366-370
Vitamin C status of an outpatient population
Johnston CS, Thompson LL
Department of Family Resources and Human Development, Arizona State University, Tempe 85287-2502, USA.
OBJECTIVE: To determine the prevalence of vitamin C deficiency (plasma vitamin C).
Concentrations less than 11.4 mumol/L) and vitamin C depletion (plasma vitamin C concentrations from 11.4 to less than 28.4 mumol/L) in an outpatient population. SUBJECTS AND METHODS: A consecutive sample of patients presenting at a health maintenance organization laboratory for outpatient procedures was utilized. Plasma vitamin C concentrations were determined in 350 females and 144 males aged 6 to 92 years (mean +/- SD: 46.7 +/- 18.7 years). RESULTS: The mean plasma vitamin C concentration for all subjects was 32.4 +/- 13.6 mumol/L. Mean plasma vitamin C did not vary by sex, race, or fasted state. Diabetics had a significantly lower mean plasma vitamin C concentration (25.6 +/- 10.8 mumol/L) compared to patients presenting for general check-up/gynecological exams (33.5 +/- 14.8 mumol/L) or pregnancy exams (32.4 +/- 9.7 mumol/L). Six percent of subjects had plasma vitamin C concentrations indicative of vitamin C deficiency (n = 31), and 30.4% of the sample were vitamin C depleted (n = 150). The prevalence of vitamin C deficiency or vitamin C depletion did not differ by race or visit category. CONCLUSIONS: Surprisingly high rates of vitamin C deficiency and vitamin C depletion were evident among generally healthy, middle class patients visiting a health care facility for routine health exams, gynecological exams, and pregnancy exams.
What happens to surplus dietary vitamin C?
Even in animals that make Vitamin C (ascorbic acid), most cell types consume ascorbic acid. This research focused on the metabolism of ascorbic acid in cells that cannot synthesize ascorbic acid and employ either the pentose phosphate pathway and glycolysis (glucose oxidation with energy production), for example human erythrocytes, or the gluconeogenic (glucose formation), as in liver cells. The addition of ascorbic acid or its oxidation product, dehydroascorbate, to erythrocytes stimulated production of lactate via the pentose phosphate pathway. On the other hand, human liver cells converted both ascorbic acid and dehydroascorbic acid to glucose.
Comment: Vitamin C is oxidized to dehydroascorbate when the former functions as a reducing agent. Certain cells such as lymphocytes regenerate vitamin C by reducing dehydroascorbate. Extra vitamin C not assimilated by tissues is excreted in the urine. What about the rest of ingested vitamin C? These studies demonstrate that peripheral cells very efficiently break down vitamin C for energy and for reducing equivalents that can regenerate reduced glutathione, among others. The byproduct of this process is lactate. When released into the bloodstream, lactate travels to the liver to be converted to glucose and used to maintain blood sugar levels. Animals that synthesize ascorbic acid from scratch employ gluconolactone oxidase, the key enzyme for vitamin C synthesis. This enzyme is located in the liver, which can therefore convert glucose into vitamin C, thus completing an “inter-organ” vitamin C cycle in these animals.
Braun L et al. Ascorbate as a substrate for glycolysis or gluconeogenesis: evidence for an inter-organ ascorbate cycle. Free Radic Biol Med 1997; 23:804-808.
Vitamin C Inhibits Ulcer-Causing Bacteria
High doses of vitamin C inhibit the bacteria that causes ulcers, Helicobacter pylori growth in culture. Vitamin C’s inhibitory effects seem to be specific to H. pylori and a close cousin, Campylobacter jejuni, but vitamin C had no effect on various gram-negative bacteria. Epidemiologic evidence and clinical experiments suggest that vitamin C may exert protective effects against the development of gastric cancer. It is estimated that 40% of the US population consumes vitamin supplements, which may account for the lower incidence of gastric cancer in the US compared with Japan, where gastric cancer is the most common cancer. H. pylori is also far less prevalent in the US compared with Japan.
Cancer 1997;80:1897-1903.
Vitamins C and E Protect Against Sunburn
Taking a combination of vitamins C and E may help protect against sunburn. The study looked at 2 grams a day of vitamin C together with 1000 international units (IU) a day of vitamin E. This study shows for the first time that systemic administration of vitamins C and E reduces the sunburn reaction in humans. There is evidence of the ineffectiveness of either vitamin C or E taken alone in protecting against UV radiation. The shielding effect seems to depend on the combined intake of both vitamins.
Journal of the American Academy of Dermatology, 1998;38:45-48.
THE ROLE OF VITAMIN C IN TUMOR THERAPY (HUMAN)
Fukumi Morishige, M.D., Dr. Med. Sci., Ph.D. Takahide Nakamura, M.D., Dr. Med. Sci. Naoko Nakamura, M.D. Noritsugu Morishige, M.D.
Fukuoka Nakamura Memorial Hospital, Fukuoka, Japan
About thirty years ago, I started administering large doses of vitamin C to post-operative patients. Its primary aim was to improve the healing of surgical wounds. During that time, I recognized that vitamin C supplemented patients very rarely suffered from post-operative and post-transfused hepatitis. This finding is from observations made on many post-operative patients especially in Kyushu district.
During the 1975 International Congress on Microbiology held in Tokyo, we presented a report of our clinical observations for the period from 1967 to 1973. The observations indicated that, the use of large doses of vitamin C remarkably reduced the occurrence of postoperative hepatitis.
Ann Nutr Metab 1997;41(5):269-282
No contribution of ascorbic acid to renal calcium oxalate stones.
Gerster H
Vitamin Research Department, F. Hoffmann-La Roche Ltd., Basel, Switzerland.
Even though a certain part of oxalate in the urine derives from metabolized ascorbic acid (AA), the intake of high doses of vitamin C does not increase the risk of calcium oxalate kidney stones due to physiological regulatory factor: gastrointestinal absorption as well as renal tubular reabsorption of AA are saturable processes, and the metabolic transformation of AA to oxalate is limited as well. Older assays for urinary oxalate favored in vitro conversion of AA to oxalate during storage and processing of the samples. Recurrent stone formers and patients with renal failure who have a defect in AA or oxalate metabolism should restrict daily vitamin C intakes to approximately 100 mg. But in the large-scale Harvard Prospective Health Professional Follow-Up Study, those groups in the highest quintile of vitamin C intake (> 1,500 mg/day) had a lower risk of kidney stones than the groups in the lowest quintiles.