TORONTO, June 8 (MedPage Today) -- A majority of the women in a breast cancer study who were questioned during follow-up said they used antioxidants during treatment, researchers said.
The finding suggests that research is needed into how the use of antioxidants such as vitamin C and beta-carotene affects treatment outcomes, Heather Greenlee, N.D., Ph.D., of Columbia University Mailman School of Public Health in New York, and colleagues, reported online in Cancer.
"Given the common use of antioxidant supplements during breast cancer treatment, often at high doses and in conjunction with other complementary therapies, future research should address the effects of antioxidant supplementation on breast cancer outcomes," they argued.
Their Long Island Breast Cancer Study Project was a case-control endeavor to examine the role of environmental influences on breast cancer among women living in New York's Nassau and Suffolk counties.
Between Aug. 1, 1996 and July 31, 1997, 1,508 women with a first primary in situ or invasive breast cancer were enrolled in the study. Between 2002 and 2004, the researchers conducted follow-up interviews among case participants.
All told, 764 women completed a full interview and gave information on antioxidant use, Dr. Greenlee said.
The interviews asked about four antioxidants -- vitamin C, vitamin E, selenium, and beta-carotene -- as well as daily dose.
Intake of each supplement was categorized as none, low, or high, with high doses defined as more than 60 milligrams of vitamin C, more than 30 IU of vitamin E, more than 20 micrograms of selenium, and more than 5,000 IU of beta-carotene.
The researchers created a nine-point "antioxidant index" to summarize total intake, based on scoring the intake of each antioxidant as zero for never, one for low, and two for high.
The antioxidant index itself was divided into three categories -- none if the total score was zero, low if the score ranged from one through four, and high if it was five or higher.
Analysis found:
- 663 participants (or 86.8%) reported receiving adjuvant treatment for their cancer and of those, 401 (or 60.5%) reported using antioxidants during adjuvant treatment.
- 120 of 310 women (or 38.7%) used antioxidants during chemotherapy, 196 of 464 women (or 42.2%) used them during radiation, and 286 of 462 women (or 61.9%) used them during tamoxifen therapy.
- 278 women (or 69.3%) used high doses (defined as doses higher than those contained in a Centrum multivitamin).
- Tamoxifen use predicted the highest relative risk for high-dose antioxidant use -- 3.66, with a 95% confidence interval from 2.32 to 5.78.
- Higher fruit and vegetable intake at diagnosis was also predictive of high use, with a relative risk of 1.71 with a 95% confidence interval from 1.13 to 2.59.
- Women who had ever used herbal products had a relative risk for high antioxidant use of 3.49, with a 95% confidence interval from 2.26 to 5.38.
- And women who had ever engaged in mind-body practices -- such as spirituality or meditation -- had a relative risk for high antioxidant use of 1.72, with a 95% confidence interval from 1.13 to 2.64.
The researchers noted that the participants from the original study who agreed to take part in the follow-up were younger, more likely to be white, and of higher socioeconomic status than women who did not respond.
"We believe our results are generalizable to similar populations," they said, although study participants "may have been heavier users of antioxidants than breast cancer patients in the general population."
The study was also limited by a relatively low response rate of about 55.4% of the participants who agreed to be contacted again after the end of the original study, they said.
The study was supported by the Lance Armstrong Foundation, the National Cancer Institute, and the National Institutes of Environmental Health and Sciences. The researchers did not report any conflicts.
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