[Medical Tribune 40(6):20, 1999. ©]
While the role of antioxidants in heart disease prevention has received much attention, some researchers now think that giving cancer patients high doses of beta-carotene and vitamins C and E may protect normal cells from the effects of chemotherapy and radiation.
Further, they contend, the antioxidants may bolster standard therapy's growth-inhibitory effects on cancer cells.
No efficacy studies in humans yet back up this claim, but in animal studies and human-cell experiments, antioxidants have shown promise, according to a review of several of these studies in the Journal of the American College of Nutrition (1999;18:13-25). The researchers said more definitive data will come later this year from an ongoing clinical trial of antioxidant treatment for cancer patients.
In the study, Kedar N. Prasad, Ph.D., lead author of the report, and colleagues, found that high doses of multiple antioxidants can not only protect normal cells during cancer treatment, but can also improve the efficacy of treatment.
A mixture of antioxidants in combination with either (3,3-dimethyl-1-triazeno)-imidazole-4-carboxamide (DTIC), cisplatin, tamoxifen or interferon a2b produced greater growth inhibition than any one chemotherapy agent alone, they reported. For example, in one study, cisplatin alone limited malignant cell production to 43 cells in vitro, compared to 18 cells for cisplatin and vitamin E.
The researchers noted that antioxidants promote tumor regression, but only at very high doses that frequently cause apoptosis. Combinations of antioxidants at lower doses, along with healthful diet and lifestyle practices, however, may improve standard cancer therapy, according to Dr. Prasad's team at the Center for Vitamins and Cancer Research at the University of Colorado Health Sciences Center in Denver.
According to Dr. Prasad, antioxidants have garnered concern among oncologists partly because they worry that high doses of antioxidant vitamins might protect not only normal cells, but also cancer cells from free radical damage produced during chemotherapy and radiation.
"But," said Dr. Prasad, "these vitamins are very selective."
Normal cells, he explained, pick up a maximum level of the vitamins and nothing more, guarding them against toxicity. Cancer cells, however, accumulate the vitamin combinations to levels that may be high enough to inhibit the growth cycle of cancer cells, according to Dr. Prasad.
Antioxidants have been studied as disease fighters because they prevent cellular damage inflicted by oxygen free radicals. However, in treating cancer, free radical damage via chemotherapy and radiation is desirable because it inhibits the growth cycle of cancer cells. Antioxidants, then, may be useful in protecting normal cells from this damage.
Another antioxidant researcher, however, thinks the Colorado team is jumping the gun. While the new report is "exciting and provocative," it really only forms the base for further research, said Jeffrey Blumberg, Ph.D., a professor of nutrition at Tufts University in Boston.