Evidence

These uses have been tested in humans or animals.  Safety and effectiveness have not always been proven.  Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Key to grades

A
Strong scientific evidence for this use
B
Good scientific evidence for this use
C
Unclear scientific evidence for this use
D
Fair scientific evidence against this use (it may not work)
F
Strong scientific evidence against this use (it likely does not work)

Grading rationale

Evidence gradeCondition to which grade level applies
A

Vitamin C deficiency (scurvy)

Scurvy is caused by a lack of vitamin C in the diet. Although scurvy is uncommon, it may occur in malnourished individuals, those that need more vitamin C (such as pregnant or breastfeeding women), or infants. If vitamin C is unavailable, orange juice can be used for scurvy in infants. Symptoms should begin to improve in 1-2 days, and end completely within seven days. Treatment should be under strict medical supervision.
B

Common cold prevention (extreme environments)

Vitamin C reduced the risk of developing colds, by roughly 50% in people under physical stress or in extreme conditions, such as soldiers in the subarctic, skiers, and marathon runners. This area merits more research and may be of particular interest to elite athletes or military personnel.
B

Iron absorption enhancement

Based on scientific research, vitamin C appears to improve absorption of iron or iron supplements taken by mouth. Further research is needed to reach a firm conclusion.
B

Urinary tract infection

Vitamin C may decrease the risk of developing urinary tract infections during pregnancy and in the elderly. Further research is needed to confirm this finding.
C

Age-related macular degeneration (AMD)

There is a lack of evidence showing beneficial effects of vitamin C alone in the treatment of AMD, an eye disorder which causes loss of vision. Further research is needed in this area.
C

Alzheimer's disease

There is limited research on the effects of vitamin C alone on the progression of Alzheimer's disease. Further research is needed before a conclusion can be made.
C

Anemia

Research has shown that vitamin C may improve the absorption of dietary iron. Limited research has shown that vitamin C may improve outcomes of anemia, a disorder where there is a short supply red blood cells. Additional research is needed before a conclusion can be made.
C

Antioxidant

Limited research showed that vitamin C lacked a clear anti-oxidant effect. Further information is required to form conclusions.
C

Arthritis (osteoarthritis, rheumatoid arthritis)

Vitamin C may slow disease progression in individuals with osteoarthritis. However, high-quality research is needed to conclude if vitamin C is beneficial for both osteoarthritis and rheumatoid arthritis.
C

Asthma

It has been suggested that low levels of vitamin C may increase the risk of developing asthma. Research on the use of vitamin C in asthma remains inconclusive. More research is needed before a clear conclusion can be drawn.
C

Autism

Ascorbic acid may decrease the severity of symptoms in children with autism, a mental disorder. More trials are needed before a conclusion can be made.
C

Bleeding stomach ulcers caused by aspirin

Early evidence suggests that vitamin C may help with stomach damage caused by aspirin. More research is needed before a clear conclusion can be drawn.
C

Breast cancer prevention

Limited research examined the role of vitamin C in breast cancer. There was a lack of conclusive results. Additional studies are needed.
C

Burns

Early research suggested that vitamin C may have positive effects in people with severe burns. Additional studies are needed before a conclusion can be made.
C

Cancer prevention

Dietary intake of fruits and vegetables high in vitamin C has been associated with a reduced risk of cancer. The role of vitamin C is unclear. Limited research showed that vitamin C supplements lacked a protective effect on certain cancers. Further research is needed to draw conclusions.
C

Cancer treatment

Vitamin C has a long history of being used as a part of cancer therapy. Clear evidence of benefit of using vitamin C is lacking. More well-designed studies are needed before a firm conclusion can be made.
C

Chemotherapy adjunct

Early research showed that vitamin C lacked additional benefit for people with cancer when together with chemotherapy, or drug-therapy for cancer. Additional studies are needed in this area.
C

Chronic venous insufficiency

Due to limitations in research, the role of vitamin C alone is unclear in chronic venous insufficiency, a disease that occurs when insufficient blood is pumped back to the heart. Additional studies are needed.
C

Colon cancer

In limited research, vitamin C lacked an effect on colon cancer occurrence or death from cancer. Additional studies are needed before a conclusion can be made.
C

Common cold treatment

The use of vitamin C for cold symptom treatment has showed mixed results in human research. Further research is needed in this area.
C

Complex regional pain syndrome

Clinical research suggests that vitamin C may be beneficial for complex regional pain syndrome, which involves long-term pain usually in an arm or leg. Further research is needed to draw conclusions.
C

Cystic fibrosis

The role of vitamin C is unclear in people with cystic fibrosis, a disease with mucus build-up in the body. Additional research is needed in this area.
C

Dementia

The role of vitamin C alone in dementia is unclear due to the limited research that is available. Further research is needed.
C

Diabetic eye disease

In limited research, the role of vitamin C for diabetic eye disease and diabetic nerve pain was unclear. Well-designed trials are needed.
C

Endometrial cancer prevention

In human research, the effects of vitamin C supplementation are mixed regarding the prevention of endometrial cancer, a cancer of the uterus lining. Further research is needed before a conclusion can be made.
C

Erythropoietic protoporphyria (EPP)

Erythropoietic protoporphyria (EPP) is a rare inherited blood disorder characterized by extreme skin-sensitivity to sunlight. More research is needed to determine if vitamin C is beneficial for this condition.
C

Exercise recovery

Vitamin C may help prevent damage to fat and muscle caused by exercise and may improve physical ability. More research is needed before a conclusion can be made.
C

Fertility

Limited research showed that vitamin C improved pregnancy rate in women with cysts on their ovaries. Further research is needed to determine the effects of vitamin C supplementation on fertility.
C

Gallbladder disease

Vitamin C supplementation may decrease the risk of gallbladder disease in women. Well-designed trials are needed to draw conclusions.
C

Heart conditions

Early evidence suggests that vitamin C supplementation may reduce the risk of abnormal heart rhythms after surgery. Additional studies are needed.
C

H. pylori infection

Adding vitamin C to standard therapy (omeprazole, amoxicillin, and clarithromycin) for stomach ulcers due to H. pylori may allow the dose of clarithromycin to be lower. Other research showed that vitamin C lacked an effect on H. pylori infection. Further research is needed to confirm this result.
C

High blood pressure

In human research, vitamin C supplementation has been shown to decrease blood pressure. Further research is needed in this area.
C

High cholesterol

According to studies in humans, vitamin C supplementation may be beneficial in people with high cholesterol. More research is needed in this area.
C

HIV (transmission)

Supplementation of mothers with HIV disease with vitamin B, vitamin C, and vitamin E may reduce child mortality and HIV transmission through breast milk. Well-designed studies are needed.
C

Ischemic heart disease

Due to its antioxidant properties, vitamin C has been used in people with ischemic heart disease, a condition where there is insufficient blood supply to the heart. Early data suggests that vitamin C may have a benefit on blood flow in the heart. Further research is needed to confirm this finding.
C

Kidney disease

Limited research suggests that vitamin C may reduce the risk of kidney disease from the dye used in coronary angiography, a procedure to examine blood vessels. Additional trials are needed before a conclusion can be made.
C

Lead toxicity

Consuming vitamin C from dietary sources may lower blood concentrations of lead. Additional studies are needed.
C

Life extension

Research has shown that vitamin C lacked effects on extending life, or preventing mortality. Further research is needed.
C

Liver disease

Administration of vitamin C in individuals with cirrhosis may have some benefit. However, in people with chronic hepatitis C, vitamin C lacked effectiveness. Additional studies are needed before a conclusion can be made.
C

Lung disease

An oxidant-antioxidant balance may play a role in maintaining proper lung function. Limited studies have examined the role of vitamin C alone for lung diseases. Additional research is needed before a conclusion can be made.
C

Metabolic abnormalities

Limited research suggests that daily high-dose vitamin C may aid with alkaptonuria, a metabolic disorder where the urine turns black upon touching air. Also, vitamin C may improve tyrosinemia in infants, a genetic disorder of tyrosine metabolism that results in problem with the liver, kidney, and brain. Well-designed trials are needed in this area before a conclusion can be made.
C

Nitrate tolerance

Vitamin C may prevent nitrate tolerance in people using nitroglycerin under the tongue. Well-designed research is needed in this area before a conclusion can be made.
C

Nutritional support (infants)

Limited research showed a lack of benefits and harmful effects of vitamin C given for the first 28 days of life in premature infants. Additional studies are needed before a conclusion can be made.
C

Parkinson's disease

Research showed that intake of vitamin E, vitamin C, and carotenoids may lack benefit for Parkinson's disease. The effects of vitamin C alone are unclear. More studies are needed.
C

Physical work capacity

Limited research suggests that higher intake of vitamin C may be related to improved physical performance and muscle strength in the elderly. Well-designed trials are needed before a conclusion can be made.
C

Plaque (on teeth)

In early research, less plaque on the teeth and less bleeding of the gums were observed after the use of vitamin C chewing gum. Further research is needed to confirm these results.
C

Pneumonia (prevention)

The role of vitamin C is unclear in the prevention of pneumonia. Further research is needed to draw conclusions.
C

Pregnancy

It is unclear if vitamin C is beneficial when taken during pregnancy. It has been suggested that preterm birth may increase with vitamin C supplementation. However, early research also shows that vitamin C may lessen the chance of early water breaking. Further research is needed. A healthcare practitioner should be consulted before taking any herbs or supplements during pregnancy.
C

Pressure ulcers

Early research shows conflicting results when taking vitamin C for pressure ulcers. Further research is needed.
C

Prostate cancer

Vitamin C has been used in prostate cancer treatment. Early evidence shows that vitamin C lacks an effect on decreasing prostate cancer risk. Further research is needed for conclusions to be drawn.
C

Proteinuria (albuminuria)

Vitamin C with vitamin E may reduce albumin in the urine in people with type 2 diabetes. Further research is needed in this area.
C

Skin aging (wrinkles)

Creams with 3-10% vitamin C may improve the appearance of wrinkled skin. Further research is needed before a conclusion can be made.
C

Skin conditions

A water-based formulation of vitamin C used on the skin may decrease skin irritation after laser treatments for scar and wrinkle removal. Well-designed studies are needed for a conclusion to be drawn.
C

Skin damage caused by the sun

Limited research showed that vitamin C applied to the skin may decrease damage caused by the sun. Further research is needed to confirm this finding.
C

Skin pigmentation disorders

Limited evidence suggests that vitamin C may play a role in perifollicular pigmentation, or increased color near the hair follicle. Additional studies are needed before a conclusion can be made.
C

Stroke prevention

Evidence is mixed for the use of vitamin C for decreasing the risk of stroke. More research is needed in this area.
C

Tetanus

Tetanus is a severe infection that may be prevented by vaccination. Vitamin C may prevent death from tetanus infection. However, more high-quality studies are needed.
C

Type 2 diabetes

The effects of vitamin C in people with diabetes are mixed. Additional studies are needed.
C

Vaginitis (inflammation of the vagina)

Early research shows that vitamin C used in the vagina may help with vaginitis, or infection and inflammation of the vagina. Further research is needed to confirm this finding.
D

Cataracts (eye disease)

Research for using vitamin C for cataracts, a disease where the vision becomes cloudy, produced mixed results. Further research is needed to draw conclusions.
D

Common cold prevention (general)

Extensive research has shown that vitamin C taken by mouth lacked an effect on cold prevention.
D

Heart disease prevention

Foods containing vitamin C have been linked to a lower risk of heart disease. However, research has shown that taking vitamin C supplements lacks an effect on heart disease prevention. Further research is needed.

Uses based on tradition or theory

The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

ADHD, allergic rhinitis, anti-inflammatory, back pain, bedsores, bladder inflammation, blood clots, blood disorders, blood vessel disorders, bloody urine, boils, bone loss, bronchitis, bursitis (joint inflammation), cervical dysplasia (abnormal pap smear), chronic fatigue syndrome (extreme tiredness that continues), clogged arteries, connective tissue disorders, constipation, dental conditions, depression, detoxification (removing toxins), drug withdrawal, endurance, excessive menstrual bleeding, fatigue, flu, fractures, glaucoma (increased eye pressure), gout, gum disease, idiopathic thrombocytopenic purpura (blood clotting disorder), immune disorders, infectious diarrhea, inflammatory skin conditions, jellyfish stings, Lyme disease, melasma (dark skin patches), mental performance, muscle soreness, prostate inflammation, sickle cell disease (abnormal blood cells), stomach ulcer, stress, toxicity, tuberculosis, urine acidification, viral infections, wound healing.

This evidence-based monograph was prepared by The Natural Standard Research Collaboration

www.naturalstandard.com