Dietary Supplements' Effect on Radiation for Prostate Cancer

Nick Mulcahy

November 06, 2009

November 6, 2009 (Chicago Illinois) — A small study of men who took antioxidant dietary supplements while undergoing radiation therapy for prostate cancer suggests that the supplements have no negative effect on treatment early on.

At 2 years, all the men in the study, including those randomized to take dietary supplements, had prostate-specific antigen (PSA) values drop as expected and remain below 1 ng/mL. Most of the men (83%) had stage 2 disease.

The phase 2 study data were presented as a poster here at the American Society for Radiation Oncology (ASTRO) 51st Annual Meeting.

Dr. Dhiren K. Shah

Two years is not a long time in terms of prostate cancer, admitted lead author Dhiren K. Shah, MD, from Cancer Care of Western New York and adjunct faculty member at State University of New York (SUNY) Buffalo.

The investigators are funded by the National Cancer Institute to follow the men for 5 years, and hope to undertake a larger, longer study on the subject, added Dr. Shah.

Many prostate cancer patients have been on vitamin supplements or go on them once diagnosed.

"Many prostate cancer patients have been on vitamin supplements or go on them once diagnosed," Dr. Shah told Medscape Oncology. "But we don't know if they are beneficial or harmful," he said. It is a question "without a clear scientific answer," he and his colleagues write in their poster.

Some laboratory evidence indicates that "antioxidants may interfere with radiation cancer-cell killing," Anthony Zietman, MD, the incoming ASTRO president, told Medscape Oncology.

Antioxidants may interfere with radiation cancer-cell killing.

"I check for patients' taking high doses of antioxidants for that reason," he said. "If a patient is on a high dose of vitamin C or E, I will ask them to stop."

However, Dr. Zietman's "first concern" about patients and supplements is that some people take "so many supplements that there is no room for food in their stomach," he said.

Some men may be on hormonal therapy without even knowing it.

He also gets the specifics: "Some men may be on hormonal therapy without even knowing it. So I ask what exactly they are taking."

Dr. Zietman, who is from Harvard Medical School in Boston, Massachusetts, explained that some dietary supplements contain phytoestrogens or even synthetic hormones, and cited the example of PC-SPES, which was banned by the US Food and Drug Administration for containing prescription drugs, including diethylstilbestrol.

Finally, Dr. Zietman talks money. "I try to get a sense of how much money they are spending on them and find out if it's too much," he said.

Beyond these concerns, Dr. Zietman thinks the use of supplements might be a good thing. "I take it as a positive sign — that a man wants to take care of himself. And perhaps there is a physical benefit, or at least a psychological one."

Centrum Silver-Like Formulation

The new trial is the first clinical study of the effects of antioxidants during radiotherapy at "self-care" dosages, according to the authors.

"We are concerned about the high doses of vitamins taken by some patients and about product claims that spur usage," said Dr. Shah about the study's background. As reported by Medscape Oncology, a manufacturer and marketer of a men's multivitamin is being sued over prostate cancer claims.

In the study, 52 men with prostate cancer were enrolled and received external-beam radiation with or without brachytherapy from 5 outpatient radiotherapy facilities.

Participants were randomized into 1 of 3 multivitamin/mineral dose groups (dietary reference intake [DRI], orthomolecular, or placebo) and asked to take capsules from 1 week prior to treatment until 3 months after treatment.

The supplements were specially designed for the study by principal investigator Jean Brown, PhD, from SUNY Buffalo.

The DRI pill is akin to Centrum Silver, a popular multivitamin, said Dr. Shah. The orthomolecular formulation mimicked the DRI pill but had extra amounts of vitamins E and C, selenium, and a number of additional ingredients. The amounts of these various nutrients were based on levels appropriate for males 51 years and older.

There was no difference in PSA response.

At 2 years, "there was no difference in PSA response," said Dr. Shah about the 3 treatment groups.

Half the men adhered to the original supplement protocol (n = 26) and half the men didn't (n = 25), but there was no difference in PSA response between the 2 groups. One man dropped out of the study.

The study also evaluated a number of clinical measures in the men at 3 months, including oxidative stress/damage, immune function, adverse effects, nutritional status, and quality of life. The investigators compared the values to baseline scores.

Nutritional status improved with both the DRI and orthomolecular pills, compared with placebo. There were no significant differences in the severity of adverse effects, depression, fatigue, or quality of life, according to the authors.

Dr. Shah and Dr. Zietman have disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 51st Annual Meeting: Abstract 2269. Presented November 3, 2009.

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