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Using Dietary & Antioxidant Supplements During Treatment

Background

Surveys investigating the use of dietary supplements (vitamin and mineral supplements) and mega-doses of antioxidants by patients with cancer during treatment, with or without the knowledge of their oncologist, reportedly ranges from 25% to 84%. Many patients are attracted to using dietary and herbal supplements during treatment for many reasons including enhancement of treatment modalities, alleviate treatment-associated side effects, improve or maintain health and nutritional status.

Currently the use of high doses of antioxidants through supplementation during treatment for cancer (e.g., radiation, chemotherapy) is very controversial. Theoretically, antioxidants might serve as beneficial agents that could enhance the effectiveness of chemotherapeutic agents potentially by blocking the generation of reactive oxidant species (ROS) by protecting the DNA of healthy cells from oxidative damage induced by chemotherapy and radiation.

Clinical Studies

Several studies have shown that high-doses of individual antioxidant micronutrients such as vitamins A, C, and E and carotenoids including ß-carotene inhibit the growth and cause differentiation and cell death in cancer cells in the laboratory. These antioxidants also reduce the growth of tumors in animal models and certain human tumors (cervical and oral cancers) without affecting the growth of healthy cells. Others believe that antioxidants may also reduce the toxicity associated with chemotherapy

Patients with cancer have also been found to have lower circulating plasma antioxidant levels before therapy than people without cancer. Whether this is due to the cancer or reduced food intake has not been determined. Conversely, other studies have reported completely opposite findings with some patients having higher antioxidant levels or no significant differences. Furthermore, observational studies report that antioxidant status is depleted during chemotherapy due to the significant degree of oxidative stress caused by the administration of anti-cancer therapies.

Current Recommendations

Unfortunately, the possible benefits of using antioxidant supplements during treatment for cancer have not been adequately studied since to date, no well-designed clinical trials have been completed to determine whether supplementations may be beneficial or harmful. Many of the published recommendations for use and dosage of antioxidant supplementation have been based on unpublished data, in vivo cell cultures, animal studies, or small scale poorly done clinical trials. Clinical studies, conducted in patients with similar types of cancer, are needed to evaluate not only whether supplements may be beneficial or detrimental, but also what doses are optimal, when should these be taken and for how long (i.e., before, during, after treatment), and are individual or combination dosages are needed. Moreover, other outcomes such as quality of life, performance status, nutritional status, tolerance to treatment, as well as impact on recurrence and survival need to be assessed. Therefore, the more commonly prevailing hypothesis today in clinical practice is that antioxidants should not be used during treatment for caner. This is based on the belief that antioxidants may protect cancer cells from oxidative damage. Furthermore, researchers recently reported that patients with unilateral, non-metastatic breast-cancer using mega-doses of ß-carotene, vitamin C, niacin, selenium, coenzyme Q10, and zinc experienced shorter survival and disease-free survival times when compared to matched controls. Other studies have found no changes in antioxidants levels with supplementation during therapy, and no reduction in toxicity related symptoms (i.e., mucositis, alopecia, stomatitis). Studies have also demonstrated that cancer cells readily absorb vitamin and contain higher vitamin C concentrations than the surrounding healthy tissue.

Currently, patients are recommended not to consume doses in excess of the tolerable upper limits of the Dietary Reference Intake (DRI) levels established for many of the vitamins and minerals (see www.nal.usda.gov/fnic). However, there are no DRI levels for plant nutrients such as ß-carotene. Actual intake levels are likely to be greater when individuals consider the amount provided by a multi-vitamin/mineral supplement in conjunction with diet consumed. Since many treatment modalities result in diminished oral intake due to nausea, vomiting, taste changes, diarrhea, mucositis, fatigue, etc., consumption of a general multi-vitamin/mineral supplement daily is recommended. Patients should be encouraged to consume a healthy diet including a variety of colorful, unprocessed foods such as fruits, vegetables, whole grains, legumes and healthy protein sources.

References:

 

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8. Lesperance ML, Olivotto IA, Forde N, et al. 2002. Mega-dose vitamins and minerals in the treatment of non-metastatic breast cancer: an historical cohort study. Breast Cancer Res Treat. 2002;76:137-143.
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