- Click here for explanation of classification scheme.

• To systematically review the scientific literature on the relationship between antioxidant intake via food or dietary supplements (tablets) and the incidence of diseases potentially associated with oxidative processes in the body
• The following antioxidants were included: Ascorbic acid (vitamin C), tocopherol (vitamin E), beta-carotene, selenium and ubiquinone (Q10)
• The diseases addressed are: Cardiovascular disease, diabetes, the most common forms of cancer, eye diseases, neurological diseases, infectious diseases and rheumatoid arthritis.

• Inclusion was based on pre-determined criteria
• The review included all original studies addressing the relationship between the selected antioxidants and certain human diseases, the relevant literature published from 1989 through 1996 and several publications from 1997.

Not described, since this was a systematic review.

• Systematic review of relevant databases (mainly MEDLINE) and a review of reference lists
• Studies were appraised by three members of the project group. A three-level scale (high, moderate, or poor scientificquality) was used to judge the scientific quality of the various studies.
• The proposed manuscript of the report was reviewed by the project group, the SBU Board of Directors, the SBU Scientific Advisory Committee and two external reviewers, Larsson LG, and Sandstrsm BM.

This review presented an overview of the findings of various studies, but did not describe the data collection used during the studies.

 

• Over 5,000 studies appear in the scientific literature
• Approximately 1,300 were found to be relevant to the hypothesis
• Approximately half of these were reviews of previously published studies in the field
• Approximately 550 (the remaining) studies were thoroughly reviewed
• Only a few studies were found to be of high scientific quality, mainly because the methods used to collect data on dietary habits contained major sources of error.

Cardiovascular Diseases

Blood lipids

• High doses of vitamin C can reduce total cholesterol in people with low plasma levels of vitamin C
• Increased vitamin E has no impact on lipids
• Insufficient data on beta-carotene and selenium to draw any conclusions.

Myocardial infarction

Prospective population-based studies show an inverse relationship with a diet rich in fruits and vegetables and dietary supplements and morbidity and morality. In addition, a relationship exists between low blood levels of  vitamin C, vitamin E and beta-carotene and increased risk for myocardial infarction. Case-control studies have yielded varying and contradictory results. Due to inconsistent results, it is difficult to draw definitive conclusions concerning the role of antioxidants in preventing cardiovascular disease.

Several randomized trials have found no benefit of antioxidant supplements. "Six different interview studies have been conducted and published. The substances given as dietary supplements mainly included beta-carotene and vitamin E. Four of these studies come from the United States, one comes from Finland and one from China. One of the studies from the United States included only persons at high risk for cancer, namely smokers, early smokers and asbestos workers. The Finnish study also addressed smokers. None of these studies, which included a total of 100,000 persons, were able to show a reduction in the risk for myocardial infarction. The Finnish study, which investigated beta-carotene and vitamin E, reported more cases of fatal cerebral hemorrhage in the group receiving vitamin E."

"Some studies of myocardial infarction also reported on stroke cases. Overall, the results do not suggest that antioxidants as a dietary supplement impact on the risk for stroke. An exception is the Finnish study mentioned above, where vitamin E increased the risk for fatal cerebral hemorrhages in smokers."

Blood pressure

Vitamin C lowers blood pressure in healthy subjects. Studies on the effects of vitamin E and selenium on blood pressure yield mixed results. No studies were found in relation to beta-carotene and blood pressure.

Blood clots

There were few studies on antioxidants and clots. A single study found that high doses of antioxidant supplements taken with food reduced clotting tendency.

Diabetes

Lack of scientific evidence supports diabetes prevention by taking antioxidant supplements.

Eye diseases

There is not enough data to support taking antioxidant supplements to prevent cataracts and macular degeneration. However, the risk of developing the serious form of macular degeneration can be reduced by consuming fruits and vegetables that are high in lutein and zeaxanthin.

Neurological Diseases

Parkinson's Disease

There were no studies on antioxidants and the prevention or delayed onset of this disease. One randomized study found no effect from vitamin E supplementation in the early stages of the disease.

Multiple Sclerosis

Analyses of some body fluids and cells suggest that antixoidants may influence this disease. However, studies in this area are of poor quality and are limited and statements cannot be made about antioxidants' preventive benefits.

Alzheimer's Disease

Vitamin E was found in one study to possibly delay progression. Both of the other studies that analyzed antioxidants used weak scientific methods, which allowed for no conclusions.

Infectious Diseases

Scientific evidence is not strong to support the prevention of these diseases by food and supplement sources of antioxidants. Vitamin C in large doses, however, may ease the symptoms of colds but not prevent them.

Rheumatoid Arthritis

There is no evidence to support a preventive role of antioxidants in this disease.

Cancer: Positive Association with Fruits, Vegetables, Antioxidants

Head and neck cancer

There is no evidence to support high intake of beta-carotene, vitamin C or selenium for reduced head and neck cancer. The studies on vitamin E yielded insufficient data to support a relationship. There may be some protective benefits from fruits and vegetables for this type of cancer. In the early stages of this cancer, beta-carotene and vitamin E supplements may have benefits.

Esophageal cancer

Intake of fruits and vegetables, but not dietary supplements, may have protective effects.

Stomach cancer

There is some scientific evidence to support consumption of fruits and vegetables to prevent this disease, but no specific antioxidant was studied.

Colon cancer

There is some scientific evidence to support consumption of fruits and vegetables to prevent this disease, but no specific antioxidant was studied. It is hypothesized that the fiber in the fruits and vegetables may have more of an effect than the antioxidant compounds contained in these foods.

Cancer: No Association with Fruits, Vegetables, Antioxidants

Lung cancer

There is little support for vitamin C and vitamin E in reducing lung cancer. No studies found protective effects for high consumption of fruits and vegetables.

Breast cancer

The role of antioxidants and fruits and vegetables is unclear. The four studies with high scientific quality do not support previous hypotheses that high intake intake of fruits and vegetables is protective.

Gynecological cancer

There is weak evidence for the preventive effects of fruits, vegetables and antioxidants on cancer of the ovaries, uterus and cervix. There may be benefits of beta-carotene against these diseases.

Prostate cancer

Overall, there is limited evidence to support the preventive role of fruits, vegetables and antioxidant supplements with prostate cancer.

"The studies are based on various methods which attempt to determine the association between antioxidants and cardiovascular disease, and have shown that a low intake of beta-carotene, vitamin C, and vitamin E are associated with an increased risk for cardiovascular disease, mainly myocardial infarction. However, several randomized studies show that beta-carotene and vitamin E, as dietary supplements, do not have this effect. To the contrary, negative effects of dietary supplements have been noted. Regarding selenium and cardiovascular disease, the data are insufficient to enable reliable conclusions. The scientific literature does not support the hypothesis that antioxidant supplements to a well-balanced diet prevent cardiovascular disease."

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