- Sodium ascorbate
For Patients & Caregivers
Vitamin C is important for maintaining general health, but vitamin C supplementation may not help lower the risk of cancer.
Vitamin C is a known antioxidant that protects the body against oxidative stress. This means that it reacts with and neutralizes free radicals in the body that can cause cellular and DNA damage. It is also important for the production of many essential molecules in the body, including proteins. Vitamin C plays an important role in the formation of collagen, which is the main structural protein in the skin. Therefore, vitamin C helps promote wound healing. Since the body cannot synthesize vitamin C, it must be gained from outside sources. In addition, scientists think that vitamin C might help reduce inflammation. However, vitamin C can make many chemotherapy drugs less effective. Patients should speak with their doctor before using vitamin C.
- To prevent and treat the common cold and upper respiratory infections
Numerous clinical trials have shown that high-dose vitamin C (around 3 grams per day) does not prevent the common cold and other upper respiratory infections, but that it can slightly reduce the duration and severity of symptoms.
- To prevent cancer
Some studies suggest vitamin C from dietary sources can reduce risk of certain cancers. However, most large-scale trials did not find vitamin C and other antioxidants useful in preventing cancers.
- To treat cancer
High doses of oral and injectable vitamin C have been used as alternative cancer treatment. Clinical studies concluded oral vitamin C is not effective, probably due to limited absorption. High-dose of intravenous vitamin C is currently under investigation as a cancer treatment.
- To treat heart disease
High dietary intake and blood levels of vitamin C have been associated with lower risk of heart disease, but a long-term study did not find benefit when taking vitamin C supplements.
- To treat cataracts
Long-term clinical trials show that antioxidant intake has no effect on development of cataracts or age-related visual loss.
- To improve wound healing
Clinical trials indicate that intravenous vitamin C benefits severely burned patients. Other clinical trials show conflicting results regarding the use of vitamin C for pressure sores or other wounds. Deficiencies in vitamin C are known to impair wound healing.
- You suffer from recurrent kidney stones: Increased kidney stone formation can occur and lead to acute kidney failure damage.
- You have kidney impairment or are on chronic hemodialysis.
- You have hemochromatosis: Vitamin C increases iron absorption, transport, and storage in the body.
- You have known G6PDH (glucose-6-dehydrogenase) deficiency: Rupture of red blood cells may occur at high doses of Vitamin C.
- You are a cancer patient undergoing radiation therapy or chemotherapy: These therapies use free radicals to kill cancer cells. Vitamin C or other antioxidants may neutralize these free radicals and lessen their effect.
- You are taking bortezomib: Vitamin C may reduce the effect of this drug.
Recent laboratory experiments and animals studies suggest that cancer cells preferentially uptake vitamin C. This raises the possibility that high-dose vitamin C may be detrimental to cancer patients undergoing radiation or chemotherapy.
It is controversial whether antioxidants like vitamin C can lessen or negate the effects of chemotherapy and radiation therapy. Because these therapies work by creating free radicals that kill cancer cells, some physicians have suggested that high levels of antioxidants can neutralize these free radicals and thereby protect cancer cells from these therapies. So what protects healthy cells may protect cancer cells as well. This question is still not fully understood and patients who are interested in taking more than the RDA of any antioxidant should consult with their doctor.
For Healthcare Professionals
Vitamin C, also known as ascorbic acid, is a water-soluble vitamin that is found in many fresh fruits and vegetables. It is essential for a variety of physiologic functions that include formation of collagen, catecholamines, and carnitine and peptide synthesis (1) . It is not synthesized in the human body, and deficiency can cause scurvy. Oral vitamin C is consumed as an antioxidant supplement for immune protection against cold and flu, for wound healing, cardiovascular health, and cancer prevention. High-dose of intravenous vitamin C has also been used as an alternative cancer treatment.
The purported effects of vitamin C have been examined in many clinical and epidemiologic studies. Regular intake of vitamin C supplements may reduce the duration and severity of common cold. However, the effect is minimal except in people exposed to acute severe physical stress (2). Vitamin C is believed to promote cardiovascular health but findings are inconsistent. Previous studies suggest that intake of dietary vitamin C, not supplements, may reduce the risk of coronary heart diseases (3). However, two large scale randomized trials did not find any benefits (4) (5). Furthermore, supplementation with vitamins C and E increased risk of mortality and nonfatal myocardial infarction in patients with coronary artery disease (6). Data on vitamin C’s effect in reducing blood pressure are also conflicting (7) (8).
Vitamin C supplementation may reduce blood glucose and lipids in type 2 diabetes patients (9). It also decreases urinary infection rates in pregnant women (10); lowers the incidence of organ failure and shortens ICU stay after surgery (11); and protects against Alzheimer’s disease (12) (13). Vitamin C can help eradicate H. pylori infection when added to standard medication regimen (14). However, antioxidants including vitamin C do not prevent or slow the progression of age-related cataract (15) or macular degeneration (16).Vitamin C may also reduce endurance training efficiency (17).
The role of vitamin C in cancer prevention is unclear. Studies indicate that vitamin C reduces oxidative stress (18). High plasma level of vitamin C is associated with lower gastrointestinal cancer incidence probably due to its protective effects against dietary carcinogenic nitroso compounds (19). Intake of vitamins A, C, or E reduced risk of cervical cancer (20), but they do not prevent gastrointestinal (21), prostate (22), lung cancers (23) and other cancer incidence or affect cancer mortality (24). Further, vitamin C supplementation is associated with increased risk of liver cancer, although this effect is not observed with vitamin C from dietary sources (25).
High-dose vitamin C has been long been used as an alternative cancer treatment (26) based on the hypothesis that the formation of new collagen resists malignant infiltration (27). Early reports using parenteral plus oral ascorbic acid showed promising results (28). But subsequent randomized, placebo-controlled trials in advanced cancer patients using 10g per day of oral vitamin C did not demonstrate any significant benefits (29) (30). This lack of effect is explained by the finding of pharmacokinetic study that ascorbic acid can only reach a limited plasma concentration through oral administration (31). A higher pharmacologic concentration, achieved only via intravenous injection, had selective cytotoxic effects on cancer cell lines (32) (33). Ascorbic acid is postulated to act as a carrier of hydrogen peroxide to the extracelluar fluid (32) where it generates free radicals against tumor cells (33). High-dose IV ascorbic acid up to 1.5g /kg/day appears to be well-tolerated (34), may improve the quality of life of terminal cancer patients (35), and reduce chemotherapy-associated toxicity in patients with ovarian cancer (67). This led to a renewed interest in studying high-dose IV vitamin C as an anticancer treatment (34) (36). However, it should be regarded as an investigational drug and used only in a clinical trial setting.
Interestingly, there is contradicting evidence against the use of vitamin C supplements during chemotherapy. In vitro and animal studies found that cancer cells preferentially uptake vitamin C (37) and render some chemotherapy drugs less effective (38). Also, a major concern surrounding use of antioxidants, such as vitamin C, is that they can interfere with the actions of chemotherapy and radiation therapy that rely on the production of reactive oxygen species for their cytotoxic activities (39). However, a clinical study showed that ascorbic acid does not reduce the therapeutic effects of paclitaxel and carboplatin (40). Another study found an increase in chemo-associated adverse effects with inadequate intake of vitamin C in children with acute lymphoblastic leukemia (41).
Adverse effects from vitamin C are rare but there are reports of gastrointestinal upset, kidney stone formation (42) , and hemolytic anemia in patients with G6PDH deficiency (43) (44) Patients with history of oxalate kidney stones, renal insufficiency, hematochromatosis, or those undergoing chemotherapy should consult their physicians before taking vitamin C supplements.
Ascorbic acid is essential for the formation and polymerization of collagen; therefore deficiency results in scurvy and poor wound healing (1). Vitamin C also inhibits hyaluronidase leading to the hypothesis that it can prevent cancer metastasis by strengthening the buildup and preventing the breakdown of collagen (45).
Ascorbic acid acts as an antioxidant to protect against oxidative damage from free radicals (46). It inactivates nitric oxide and improves endothelium-dependent vasodilation (47), and acts via different mechanisms depending on its plasma concentration. Plasma concentrations <0.1mM is achieved through oral intake of dietary or supplemental forms. At pharmacologic plasma concentrations of 0.3 - 20mM via intravenous injection, ascorbic acid is oxidized to an ascorbate radical which acts as prodrug for hydrogen peroxide formation within interstitial fluids (33). This induces DNA damage and adenosine triphosphate (ATP) depletion, and triggers ataxia telangiectasia mutated (ATM)/adenosine monophosphate–activated protein kinase (AMPK) and inhibition of mammalian target of rapamycin mTOR in ovarian cancer cells (67).
Ascorbate decreases colon cancer cell proliferation by downregulating specificity proteins (Sp) (48). It depletes ATP and induces autophagy and cell death in prostate cancer cells (49). Preferential oxidative cytotoxic effects on cancer cells may be due to the presence of intracellular iron (50), copper (51), an increase in p53 activity (52), and overexpression of sodium-dependent vitamin C transporter 2 (SVCT-2) (53).
Dehydroascorbic acid, the oxidized form of vitamin C, may have cytoprotective effects by preserving mitochondrial membrane potential (38).
Common: Nausea, diarrhea and stomach cramps
Reported (oral): In patients with a history of kidney stones, increased oxalate kidney stone formation occurs with possible nephrolithiasis, acute renal failure, or renal insufficiency (42) (58) (59).
Reported (oral): In patients with G6PDH deficiency, hemolytic anemia may occur at high doses (43) (44).
Reported (oral): Severe cyanide poisoning following ingestion of 3 grams of amygdalin with concurrent use of 4800 mg of vitamin C per day (60).
Reported (oral): Excessive use of chewable tablets may break down tooth enamel, increasing the risk of dental caries (61).
Iron: Ascorbic acid increases iron absorption and modulates transport and storage in the body. Significant in patients with hematochromatosis (61).
Chemotherapy drugs: Vitamin C can reduce the effectiveness of many antineoplastic agents, including vincristine, doxorubicin, methotrexate, cisplatin, and imatinib (38).
Bortezomib: Ascorbic acid intake reduces the activity of bortezomib (62). In a clinical trial using these agents together, the interaction is minimized by administrating bortezomib in the morning and ascorbic acid in the evening (63).
Glutathione: Glutathione, as an antioxidant, reduces the prooxidant cytotoxic effects of ascorbic acid (64).
Beta-blockers: Ascorbic acid can enhance the cardioprotective effects of beta-blockers in post-bypass patients (65).