Vitamin C, or Ascorbic Acid is a water-soluble micronutrient. Perhaps this vitamin is best known for when it was discovered as the heroic cure for Scurvy. It plays a critical role in collagen synthesis which is a one of the body's main proteins. Due to this vital role it plays in manufacturing stabilized collagen, it is very important for wound repair, healthy gums, and for prevention of easy bruising. Vitamin C is also vital for immune function, the synthesis of some nerve transmitting substances and hormones, carnitine synthesis, and the absorption and utilization of other nutrients. Vitamin C is also an important antioxidant.
The following foods have the highest concentration of vitamin C. For a more expansive list on food sources of specific nutrients visit Health Canada's Dietary Reference Intakes for Vitamins or USDA's National Nutrient Database
Other food sources include:
It is important to eat fruits and vegetables after they have been freshly cut as exposure to air overtime actually destroys the vitamin C and thus decreasing the vitamin C content.
- Asthma and other allergies: There is evidence to suggest that low vitamin C is an independent risk factor for asthma. Vitamin C plays an important role as an antioxidant particularly in the lungs and airways. Asthmatics require more vitamin C than individuals in the general population and supplementation has shown to improve the condition. Vitamin C also acts as an antihistamine, thus helping with other allergies as well. It is recommended, however, that supplementation of vitamin C must occur overtime to see an antihistamine effect.
- Atherosclerosis, elevated Cholesterol levels, and High Blood Pressure: High dietary intake of vitamin C significantly reduces risk of death from stroke and heart attack. Vitamin C works as an antioxidant to prevent oxidation of LDL cholesterol and regenerates vitamin E (another potent antioxidant); strengthens the collagen in the arteries, lowers total cholesterol and blood pressure, raises HDL (good cholesterol), and inhibits platelet aggregation.
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- Cancer Prevention: Vitamin C's role as an antioxidant also contributes to its function as a cancer preventive agent. It has shown preventive capabilities towards cancers of the lung, colon, breast, cervix, esophagus, oral cavity, and pancreas. Increasing dietary intake of foods with vitamin C is important as they also contain other cancer-preventive compounds.
- Cancer Treatment: According to studies, it appears that vitamin C plays a more effective role in preventing rather than treating cancer but evidence is not conclusive. With that said, many have been able to show the benefit of high-dose vitamin C during cancer treatment for its immune enhancing and antioxidant effects.
- Cataracts: Antioxidant-rich nutrients play a role in both preventing and treating cataracts. In some cases it has even shown to improve vision. The lens of the eye requires large amounts of vitamin C; serum levels must be very high in order to allow for concentration of the vitamin in the tissues with highest demand (liver, spleen, and lens of the eye).
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- Common Cold: Vitamin C has been shown to reduce the symptoms of the common cold as well as the duration.
- Parkinson's Disease: Vitamin C and other antioxidant nutrients are effective in slowing down the progression of the disease for patients not yet on medications. High doses are required in order to achieve antioxidant activity in the brain (oxidative damage in a Parkinson's patient is thought to have been caused by a neurotoxin affecting the basal ganglia and leading to the disease). Drug treatment is ultimately delayed in those receiving nutrient therapy.
- Skin Ulcers and Wound Healing: Vitamin C has been shown to both prevent and treat bedsores.
- Pregnancy-Related Concerns:
- Preeclampsia: The triad of symptoms seen in preeclampsia are: high blood pressure, fluid retention, and protein-loss in the urine, and can be detrimental to the fetus. Low antioxidant levels may be a predisposing factor in preeclampsia.
- Prevention of Premature Rupture of Fetal Membranes (PROM): PROM can have negative consequences for a fetus. Low levels of vitamin C can be a risk factor. This could be due to reduced collagen content in the amniotic sac and therefore decreasing its integrity.
- Prevention against side effects of vaccinations: Histamine levels increase post-vaccination and contribute to many of vaccines side effects. Preventive doses of vitamin C taken before vaccination may act to clear blood levels of histamine which occur after vaccination.
- Other Uses: anti-aging, stress reduction, constipation, thrombocytopenia purpura
Scurvy is likely the best known nutrient deficiency which is cause by a vitamin C deficiency. Symptoms include:
- bleeding gums
- poor wound healing
- extensive bruising
- increased susceptibility to infection
Vitamin C at high doses is tolerated in most people. Side effects for some may include:
These effects are dose dependent and can be reversed by taking a lower dose that is more tolerable. Dosing to bowel tolerance is a common method used to achieve a therapeutic dose for an individual.
Common Deficiency Test:
- Serum Vitamin C
- Ascorbic acid is the best option for most individuals. It is the cheapest form and most widely used. Buffered forms can be easier on people's stomachs; vitamin C is buffered with sodium, magnesium, calcium, or potassium. Sodium ascorbate may be a problem for individuals with sodium sensitivity.
- For individuals sensitive to corn, there are corn-free products available derived from the sago palm.
- Ester-C is another form available. Claims are made that it is better absorbed, however, studies have not found this to be true. It is also more expensive than regular vitamin C.
- Bioflavonoids taken at the same or equal amount as vitamin C enhances absorption.
- Vitamin C can be found in crystals, powders, capsules, tablets, and time-released tablets.
- The recommended dosages varies based on age and health status. To determine what your specific requirements are talk to your naturopathic doctor or other trained medical professional.
- Infant: 30mg (under 6 months); 35mg (6-12 months)
- Child: 40mg (1-3 years); 45mg (4-10 years); 50mg (11-14 years)
- Adult: 60mg (15+ years)
- Pregnancy: 70mg
- Lactation: 95mg
- Children: There was one small study involving two infants done in 1965 which suggested that infants can experience "rebound scurvy" if their mothers were taking mega doses of vitamin C during gestation. So called "rebound scurvy" was said to occur as a result of abrupt cessation of the mega dose of the vitamin at birth. This evidence has not been supported since. The risk is considered very low. 
- Adults: no reported concerns.
- Seniors: no reported concerns.
- Pregnancy: Pregnant women should avoid doses of 500mg or greater without close medical supervision.
- Breastfeeding: no reported concerns.
- Glucose-6-phosphate dehydrogenase deficiency
- Individuals with a history of hemosiderosis, hemochromatosis, other forms of iron overload
- Individuals with a history of recurrent nephrolithiasis especially oxalate stone-formers - should avoid daily doses of 1000mg or more without medical supervision
- Mega doses (>4g/day) in individuals with history of renal failure without medical supervision
- Doses of greater than 1000mg is generally contraindicated during chemotherapy and radiation in which free-radical formation is intentional
- Precautions and Warnings:
- Renal impairment or on chronic hemodialysis - doses should not exceed 100-200mg/daily
- Sickle cell anemia, sideroblastic anemia, thalassemmia - caution and close supervision
- Individuals preparing for major surgery (especially with increased risk of hemorrhage) - should not exceed 400mg daily in the week before procedure except under medical supervision
- Sensitivities to corn and corn products - some commercial brands of vitamin C are derived from corn and persons may react; use ascorbates derived from sago palm
- Long term use of high doses of vitamin C may induce copper deficiency.
- Drug Interactions include:
- Supportive or Beneficial:
- Acetaminophen - Not fully understood or adequately researched, but supervised co-administration of vitamin C with acetaminophen may enable reduced drug dosages and help protect against hepatotoxicity.
- Acetylsalicylic Acid (Aspirin) and Salsalte - Drug can increase urinary excretion of vitamin C, lower leukocyte ascorbic acid levels, and decrease its metabolic availability. Compromised nutritional status can increase adverse effects of drug. Vitamin C may reduce gastric mucosal damage and gastric toxicity induced by ASA-generated free radicals. Co-administration of vitamin C and other antioxidants may also potentiate aspirin's antiaggregative effect.
- Antihypertensive Medications - Enhanced levels of the vitamin may play a protective role against reactive oxygen species associated with essential hypertension and endothelial dysfunction and may benefit blood pressure management.
- Cimetidine and Related Histamine (H2) Antagonists - Vitamin C can prevent a cimetidine-induced decrease in CYP450 activity and may normalize serum hydrocortisone concentrations.
- Corticosteroids, oral - Co-administration of Ascorbic Acid with glucocorticoids may enhance their therapeutic activity and reduce adverse effects of extended use, including vitamin C depletion.
- Cyclosporine - Co-administration of vitamin C and possibly other antioxidants with cyclosporine may reduce adverse effects without decreasing therapeutic efficacy. However, drug dose needs to be monitored closely and possibly reduced because vitamin C could enhance bioavailability and decrease the clearance and steady-state volume of drug's distribution.
- Desferoxamine and Related Chelating Agents - IV vitamin C may increase iron excretion by deferoxamine. Close supervision and monitoring are warranted, particularly in individuals with cardiac disease.
- Disulfiram - Co-administration can enhance therapeutic efficacy by reducing adverse effects and supporting drug compliance. Proper training required.
- Erythropoiesis-stimulating Agents - IV Ascorbic Acid reduces anemia in iron-overloaded, EPO-hyporesponsive hemodialysis patients and facilitates elimination of iron from stores without reducing functional iron levels.
- Furosemide and Related Loop Diuretics - Co-administration appears to significantly increase bioavailability of furosemide and enhance its diuretic and natriuretic effects. It also helps to prevent depletion.
- Levodopa, Carbidopa, and Related Antiparkinsonian Medications - Administration of vitamin C (and vitamin E may slow the disease progression in Parkinson's patients. Co-administration of moderate-dose Ascorbic Acid (and vitamin B6 and CoQ10) with levodopa-carbidopa may be beneficial but needs to be gradually introduced, closely supervised, and regularly monitored. High-dose vitamin C is contraindicated in certain patients who may experience an exacerbation of dyskinesia.
- Methotrexate - Consider co-administration of vitamin C in moderate to high dose to alleviate nausea associated with drug use. Use of antioxidants during chemotherapy is generally contraindicated outside context of medical care by trained and experience clinicians.
- Nitroglycerin and Related Nitrates - Co-administration may prevent or reduce development of tolerance, at least in part, by mitigating free-radical formation.
- Tetracycline Antibiotics - Concomitant intake can enhance bioavailability and elevate blood levels of tetracycline. It may also protect against adverse effect of drugs. Concomitant use also addresses a drug-induced deficiency.
- Addresses Drug-Induced Deficiency:
- Oral Contraceptives - Monitor for adverse effects of oral contraceptives especially in women with compromised nutritional status. Consider co-administration of vitamins C, B12, B6, as well as folate and magnesium in women demonstrating or at risk of adverse effects of exogenous estrogens. Although most evidence indicates that vitamin C supplementation is unlikely to interfere with the intended activity of oral contraceptives, it is always prudent to be watchful for an indications that vitamin supplementation might be impairing drug activity.
- Chemotherapy and Radiotherapy - Unsupervised co-administration of high-dose vitamin C is generally contraindicated. Co-orinated care using high doses of IV Ascorbic Acid may be beneficial with experienced clinicians.
- Indinavir and Related Protease Inhibitors - Concomitant high-dose ascorbic acid can reduce steady-state plasma concentrations of indinavir. If nutrients indicated, monitor drug levels.
- HMG-CoA Reductase Inhibitors (Statins) - Concomitant vitamin C may improve some lipid parameters (particularly LDL and triglycerides), promote glutathione, protect and regenerate vitamin E, and inhibit lipid peroxidation, all of which may contribute to reducing cardiovascular risk. However, the interaction between statins and antioxidants is controversial, and evidence suggests potential impairment of HDL-ogenic effects of niacin by antioxidants. Avoid combinations in some cases.
- Lansoprazole-amoxicillin-metronidazole (LAM) Triple Therapy - LAM triple therapy enhances gastric vitamin C levels and recovery from gastritis, but eradication of H. pylori is not enhanced and may be impaired by simultaneous administration of vitamin C (and vitamin E).
- Propranolol and Related Beta-1-Adrenoceptor Antagonists (Beta-Adrenergic Blocking Agents) - Vitamin C may decrease the absorption and first-pass metabolism of propranolol, but this interaction appears to be of minimal clinical significance. Separate oral intake if vitamin C is indicated.
- Nutrient Interactionsinclude: 
- Alpha Lipoic Acid - Demonstrate synergistic activities against free radicals. Antioxidants pose less risk of become pro-oxidants when administered together.
- Bioflavonoids - Synergistic activity is also demonstrated with vitamin C and bioflavonoids. Bioflavonoids also increase the bioavailability of vitamin C; vitamin C protect flavonoids from oxidation.
- Copper - Concomitant vitamin C may cause copper depletion but evidence is inconclusive and clinical significance has not been established.
- Folic Acid - Vitamin C appears to play an important role in folic acid activation.
- Glutathione - Hepatic glutathione plays an essential role in regeneration of vitamin C. Co-administration allows for synergistic enhancement of both agents.
- Grape Seed Extract - Authors of one study suggest using caution for hypertensive individuals taking supplements containing combinations for vitamin C and polyphenols (compound found in grape seed extract). Further research is needed to confirm and determine the clinical significance.
- Iron - Vitamin C enhances absorption of non-heme iron in the GI tract and increasing its bioavailability by 2-3 fold. Risk of adverse reaction may be seen in individuals with genetic hematochromatosis or other issues of iron-overload.
- Lutein - Vitamin C administered simultaneously facilitated increased lutein absorption.
- Selenium - Vitamin C appears to play an important role in selenium homeostasis. It is suggested that selenium be ingested 1 hour before or 20 minutes after taking vitamin C as vitamin C at doses greater than 1g may reduce absorption.
- Vitamin B6 - Urinary excretion of B6 may be increased in individuals with vitamin C deficiency. In individuals with risk of renal oxalate calculi due to high-dose vitamin C, Vitamin B6 has been shown to normalize the oxalate production and excretion.
- Vitamin B12 - Some suggest that vitamin C in high-doses damages or diminishes B12 effectiveness. Separate intake.
- Vitamin E - Vitamin E and C are part of an important antioxidant network whereby vitamin C aids to regenerate vitamin E and restore its antioxidant capability.
- Vitamin K - One study found that co-administration of vitamin K3 and ascorbate provided relief of nausea and vomiting of pregnancy. Vitamin K2 with IV ascorbate has been show recent promise as an oxidative therapy for cancer.
- Medlineplus 
- Hoffer Abram, Prousky Jonathan (2006) Naturopathic Nutrition, A Guide to Nutrient-Rich Food & Nutritional Supplements for Optimum Health, CCNM Press
- Murray Michael T (2005) Encyclopedia of Nutritional Supplements, The Essential Guide for Improving Your Health Naturally, Prima Publishing
- Bralley J Alexander and Lord Richard S (2005) Laboratory Evaluations in Molecular Medicine, Nutrients, Toxicants, and Cell Regulators Institute for Advances in Molecular Medince, GA
- Stargrove Mitchell Bebell, Treasure Jonathan, McKee Dwight L (2008) Herb, Nutrient, and Drug Interactions, Clinical Implications and Therapeutic Strategies. Mosby