MIAMI BEACH, Fla.—Despite past safety concerns, prostate cancer (PCa) patients who use the antioxidant supplement beta-carotene during radiation therapy do not appear to have an increased risk of dying from the disease 10 years after treatment, according to a study presented at the 53rd Annual Meeting of the American Society for Radiation Oncology.

The safety of supplemental dietary antioxidants during radiation therapy is controversial. Antioxidants could potentially counteract the pro-oxidant effects of radiation therapy and reduce its effectiveness. Beta-carotene is an antioxidant that is converted in the body to vitamin A.

“We are encouraged by our long-term findings, since many patients who receive radiation therapy for prostate cancer also take dietary supplements, and it is important to understand the potential benefits and harms of taking these supplements,” said Danielle Margalit, MD, MPH, a radiation oncologist at the Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Boston.

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The study is part of the Physicians’ Health Study (PHS), a large randomized phase 3 trial of aspirin and beta-carotene that started in 1982. Investigators wanted to find out if the use of the supplemental antioxidant beta-carotene during radiation treatment for PCa increased the risk of death from the malignancy. The investigators performed a prospective study nested within the PHS to investigate if there was an association with an increased risk of PCa death or metastases.

The randomized study involved 383 men who received radiation therapy for PCa and were previously randomized to receive either beta-carotene (192 patients) or placebo (191 patients).

The mean age of the men at diagnosis was 73 years (range: 68-76 years old). The primary endpoint was time from radiation therapy to lethal PCa (either PCa death or bone metastases).

After 10.5 years of follow-up after radiation therapy, investigators observed no significant difference between the groups in the risk of dying from PCa. After adjusting for age at radiation therapy, PSA levels, Gleason score, and clinical stage, the difference remained non-significant.  Overall, the 10-year rate of freedom from lethal prostate cancer was 92% in the beta-carotene group and 89% in the placebo group.

“It is important for physicians and patients to discuss nutrition during radiation therapy,” Dr. Margalit said. “At Dana-Farber Cancer Institute, we generally recommend a multivitamin and emphasize the importance of tobacco cessation, especially during radiation therapy. However, each patient’s situation is unique and specific supplements can also interact with certain chemotherapy agents.”

She and her colleagues are now studying the safety of using the common antioxidant supplements vitamin E and vitamin C during radiation therapy for PCa.