The only specific therapeutic use of Vitamin C is the prevention and treatment of scurvy.
Vitamin C and skin injuries
Vitamin C supplementation is also used to treat ulcers, burns and injuries, because of its ability to stimulate collagen formation.
Vitamin C in cancer treatment
High doses of vitamin C are used as adjuvant treatment for cancer because of research findings which indicate that it could possibly slow the growth and proliferation of cancer cells in prostate, pancreatic, liver and ovarian cancers, among others.
While conclusive evidence is lacking, vitamin C in high doses also appears to improve the quality of life in cancer patients. It not only reduces the severity of symptoms such as vomiting, nausea, tiredness, pain and anorexia, but also elevates the mood and produces an overall improvement in physical health.
It is important to realize that cancer cell response to vitamin C is variable, possibly due to genotypic variations which determine the presence or absence of enzymes such as catalase, which confer resistance to the cytotoxic effects of vitamin C.
Vitamin C may be administered intravenously or orally. Intravenous administration leads to higher serum levels than when it is given by mouth, since it bypasses intestinal absorption barriers.
Vitamin C in prophylaxis of chronic disease
Vitamin C supplementation is also useful in preventing chronic disease, according to some studies.
Vitamin C and cardiovascular disease
Supplementation with vitamin C was associated with a reduction in cardiovascular risk, including heart attacks. In one study which used a precise measurement of biologically available vitamin C, every increase in plasma vitamin C concentration by 20 μmol/L was associated with a 9% reduction in heart failure risk.
Overall mortality from all causes, cardiovascular disease and cancer (the latter only in men) shows a strong inverse association with plasma vitamin C concentrations, such that for each 20 μmol/L increase in plasma concentration, there was a 20% decrease in risk.
Other research showed some evidence of significant reduction in cholesterol levels, but no effect on cardio-protective HDL. Overall results seem to indicate that 400 mg or more of vitamin C are required each day to achieve the greatest lowering of cardiovascular risk.
Vitamin C supplementation with 500 mg/day appears to have benefit in the treatment of conditions such as hypercholesterolemia, diabetes mellitus, hypertension, coronary heart disease, angina pectoris, and congestive cardiac failure. Treatment with vitamin C, consistently improves the blood flow to vital organs by vasodilation. This level of supplementation for 8 weeks reduced blood pressure modestly in hypertensive and normotensive patients. Similarly, plasma vitamin C measurements indicate an inverse association between the blood pressure and vitamin C concentration.
Vitamin C and stroke
Some evidence exists that higher vitamin C levels are linked to approximately 30% reduction in the risk of stroke. This has been confirmed by other studies, with the proviso that the beneficial effects may be due to the health-boosting effects of a diet rich in fruits and vegetables, which is often the primary source of vitamin C. In fact, vitamin C levels may serve as a good biomarker for lifestyle factors that reduce the risk of cerebrovascular events.
Vitamin C and cancer prevention
While research has not shown convincing evidence of a link between vitamin C and overall cancer incidence, the risk of breast cancer was 63% lower in overweight women who had an intake of 110 mg/day of vitamin C as compared to controls. This remains to be confirmed.
Stomach cancer risk may also be reduced by higher vitamin C concentrations, perhaps by reducing carcinogenic N-nitrosoamine production. Again, vitamin C is capable of inactivating the enzyme urease, which is important in the survival of Helicobacter pylori and colonization of the gastric mucosa.
Since this is a known risk factor for gastric cancer, vitamin C prophylaxis may be effective in preventing this conditions. However, it also reduces gastric acidity, and so may be considered especially in those patients without achlorhydria.
Vitamin C and immunity
Vitamin C stimulates several immune functions, such as cellular motility and phagocytosis, resistance to oxidative damage, and interferon release. Whether this leads to superior immune function as a whole is a topic that is still under study.
When used to prevent the common cold, vitamin C is found to cut the incidence in half when administered to those undergoing great physical strain, an effect which was not observed under ordinary circumstances.
Regular ongoing vitamin C supplementation does reduce the duration of colds by about 14% in children, but only 8% in adults. It has no known clinical effect when started after a cold has begun. Vitamin C is sometimes used as adjunctive treatment in infections, such as tuberculosis, at a dose of 500 mg a day, which keeps the level near blood saturation point.
Vitamin C and other medical conditions
The incidence of gout showed a consistent inverse association with vitamin C supplementation.
Colon cancer risk may be modestly reduced with dietary vitamin C and supplementation, as also the risk of non-Hodgkin’s lymphoma.
Other disease conditions which are inversely related to dietary (not supplemental) vitamin C levels include Alzheimer’s disease and cataracts of the ocular lenses related to aging processes.
Vitamin C administration appears to reduce the exercise-induced reduction in FEV1 that is characteristic of exercise-induced asthma.
Vitamin C supplementation may reduce blood lead levels and thus prevent lead toxicity, via unknown mechanisms.