Influence of anti-cancer therapy on antioxidant level
Chemotherapy lowers total antioxidant status. However, studies of changes in vitamins C, E, selenium and beta-carotene found no consistent patterns associated with chemotherapy. This may be due to the fact that patients were depleted of antioxidants before initiation of treatment probably because cancer cells metabolize antioxidant vitamins more efficiently than normal cells.
This hypothesis is supported by studies that found that cancer patients had lower levels of antioxidants than controls even before administration of chemotherapy and may suggest that low antioxidant status may be associated with neoplastic activity and supports the assumption that antioxidant supplementation could benefit cancer patients.
Initiation of anticancer therapy may also lower levels of antioxidants by affecting dietary intake.
The observation that TRAP (a measure of total antioxidant capacity) levels consistently decreased while individual antioxidants show no consistent changes suggest that factors other than known antioxidants may contribute to changes in total antioxidant status of the body during chemotherapy.
Clinical trials suggest that individual antioxidants administered in conjunction with conventional therapy may affect serum values for some nutrients but not others. Selenium supplementation appears to have the most consistent effect on selenium levels in patients undergoing chemotherapy.
Observation
Antioxidant supplements may reduce the frequency and severity of toxicity associated with anticancer therapy and make it possible to administer higher and more effective doses of chemotherapy.
A major difficulty in determining the effects of antioxidants in clinical trials is the variability of doses, timing and duration of supplementation applied in these trials. The recommended dietary allowances (RDA) for vitamins and minerals are commonly applied to cancer patients, but these RDA values are intended as guidelines to prevent nutrient deficiencies among healthy individuals and may not be suitable for patients undergoing cancer therapy.
Additional studies investigating the effects of antioxidants on chemotherapy should be incorporated into large-scale phase III clinical trials in relatively homogenous patient populations receiving well-specified conventional treatment protocols.
These studies should control for behavioral factors, such as the use of complementary medicine, patient compliance and carcinogen exposure such as tobacco among lung cancer patients.
Much more work is needed to establish a clear role for the use of dietary supplements as an adjunct to cancer chemotherapy.
Chang Yok Ying
Principal pharmacist
Pharmacy Department
National Cancer Centre Singapore
References:
- Elena J. Ladas et al., Antioxidants and Cancer Therapy: A systematic review JCO2004 vol 22 no.3
- Keith Block ,MD. Study on role of antioxidants in reducing chemotherapy toxicity. A systematic review of randomized controlled trials. ASCO 2007 Abstract no.9130
- Kenneth A. Conklin. Dietary antioxidants during cancer chemotherapy: Impact on chemotherapy effectiveness and development of side effects. Nutrition and cancer, 37(1), 1-18, 2000
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