Vitamins A, C, and E in Cancer Therapies
Abstract & Commentary
Synopsis: Vitamin E and vitamin C supplements are recommended in modest doses, as they are safe and may help prevent some cancers.
Source: Kaegi E. Can Med Assoc J 1998;158:1483.
Because large doses of supplemental vitamin a have serious toxic effects, retinoids like beta carotene (a provitamin—i.e., transformed in vivo into vitamin A) have been touted as treatment for some cancers. There are laboratory and animal data to suggest the increased production and tumoricidal activity of white blood cells and macrophages with retinoids, especially beta carotene and analogues of vitamin A. Clinical data are contradictory, though recent studies suggest an increased incidence of lung cancer with beta carotene supplementation.
Although epidemiologic data suggest a preventive effect of foods rich in vitamin C against stomach and cervical cancer, either through an antioxidant or nitrosamine blocking action, the therapeutic effects of supplemental vitamin C are less clearly documented. Anecdotal reports and uncontrolled case series suggest improved survival, although two randomized controlled trials of vitamin C therapy with advanced cancer were negative. Safety at up to 1000 mg daily has been repeatedly reported. Proponents believe that megadose, intravenous vitamin C earlier rather than later in illness, has a better chance of having a beneficial clinical effect.
Like vitamin A, vitamin E is fat soluble. It is most commonly ingested in food as d-tocopherol, usually gamma, and as a supplement, most of which is synthetic, or dl-alpha tocopherol. Most clinical trials have been done with dl-alpha tocopherol. Vitamin E’s lipid antioxidant and immunostimulatory effects are thought to be responsible for its anticancer effects. Toxicity with high doses—over 800 IU—can include nausea, diarrhea, and blurred vision. High doses may also interfere with the absorption of anticoagulants, iron, and vitamin B12. Oral leukoplakia, a cancer precursor, may be successfully treated with vitamin E, and invasive prostate cancer risk may be reduced with 50 mg (approximately 100 IU) daily.
Comment by John La Puma, MD
Vitamin E and vitamin C supplements are recommended in modest doses, as they are safe and may help prevent some cancers. Beta carotene supplements may be dangerous and are not recommended. Strong cancer prevention data, especially for gastrointestinal disease, exist for low saturated fat diets that are rich in high fiber, largely unprocessed plant foods. A diet that puts fruits, vegetables, grains, and legumes in the middle of the plate and makes animal foods side dishes is probably the best medicine. Because 250 almonds or hazelnuts are needed for 100 IU of vitamin E daily, however, a supplement is the best way to get this vitamin. (Dr. La Puma is Director, C.H.E.F. Skills Research, Cooking, Healthy Eating, and Fitness [C.H.E.F.]. Alexian Brothers Medical Center, Elk Grove, IL.)