Many women with breast cancer continue to take antioxidant supplements despite worries that the pills may interfere with treatment, a new study shows.

The report, published in the July issue of the medical journal Cancer, is the latest to raise concerns about the large number of cancer patients turning to megadoses of vitamin and mineral supplements in hopes of boosting their health.

Some research suggests that high doses of antioxidants, such as vitamins C and E, beta-carotene and selenium, may interfere with radiation and some types of chemotherapy. Those treatments attack tumor cells by generating free radicals, which vitamin supplements may essentially “clean up,” preventing them from attacking the cancer. Other studies suggest that just like healthy cells, cancer cells thrive in the presence of high doses of antioxidants.

Researchers at the Columbia University Mailman School of Public Health tracked the use of antioxidant supplements among 764 women in the Long Island Breast Cancer Study Project. Among the 663 women who were receiving chemotherapy, hormone treatment or radiation for breast cancer, 60.5 percent said they were taking antioxidants during breast cancer treatment.

Most of the women (70 percent) said they were taking high doses of the supplements, which was defined as a dose larger than that found in a popular multivitamin. The study only looked at the prevalence of antioxidant use among women with breast cancer and didn’t measure whether any of the women experienced negative effects as a result. In addition, the research focused on antioxidants taken in pill form. Most doctors believe high consumption of fruits and vegetables, which contain vitamins and antioxidant compounds, doesn’t pose any additional risk to cancer patients and may be beneficial.

The rate of vitamin use is higher among cancer patients than in the general population. Last year, researchers at the Fred Hutchinson Cancer Research Center in Seattle reviewed 32 studies conducted between 1999 and 2006 and found that 64 percent to 81 percent of cancer survivors in the studies were taking extra vitamins or minerals beyond multivitamins. In the general population, only 50 percent of American adults reported taking dietary supplements.

The American Cancer Society has said vitamins and supplement shouldn’t be used during cancer treatment. A 2005 report in the medical journal CA cites several studies that show the use of vitamins by cancer patients doesn’t help and may even cause harm.