Published: Oct 10, 2013 | Updated: Oct 11, 2013
By Charles Bankhead, Staff Writer, MedPage Today

Full Story:  http://www.medpagetoday.com/HematologyOncology/BreastCancer/42208

Postmenopausal breast cancer patients had a significantly lower risk of dying of the disease if they consumed multivitamins with minerals, an analysis of data from the Women’s Health Initiative (WHI) showed.

Overall, use of multivitamins with minerals was associated with a 30% lower likelihood of breast cancer mortality in women who were already taking the vitamins at diagnosis. A matched analysis yielded a similar reduction in the hazard for fatal breast cancer.

“This large prospective study among U.S. older women showed a consistent association between multivitamin and mineral use and lower breast cancer mortality,” Sylvia Wassertheil-Smoller, PhD, of Albert Einstein College of Medicine in Bronx, N.Y., and co-authors reported online in Breast Cancer Research and Treatment. “Such suggestive evidence of benefit of multivitamin with minerals in the breast cancer setting is intriguing but should be followed up in future investigations.”

Despite widespread use of multivitamins in the U.S., little information has accumulated regarding the relationship between vitamin consumption and breast cancer mortality in women with newly diagnosed breast cancer. An earlier analysis of WHI data showed no association between multivitamin use and the risk of developing breast cancer.

A handful of other observational studies produced inconsistent results regarding associations between vitamin intake and the risk of breast cancer, other diseases, or overall mortality.

Whether multivitamin use affects breast cancer mortality remained unclear. To examine the issue investigators analyzed data for 8,048 women who developed breast cancer during follow-up in the WHI.

WHI comprised 161,608 women ages 50 to 79, enrolled at 40 clinical centers in the U.S. from 1993 to 1998. Multiple observational studies and clinical trials were conducted in the WHI patient population, and participants could be enrolled in overlapping studies. The 8,048 participants included in the analysis comprised women from the observational studies and clinical trials.

Use of dietary supplements and medication were documented at each follow-up visit. At each visit, participants were asked whether they had used vitamins at least once a week during the previous 2 weeks. Wassertheil-Smoller and colleagues did not have information about frequency of vitamin use.

The data showed that 40.4% (3,240) of participants reported vitamin use at baseline, including 2,920 who used multivitamins with minerals (the remaining participants using multivitamins only). During a mean follow-up of 7.1 years from breast cancer diagnosis, 518 WHI participants died of breast cancer.

The primary analysis considered use of multivitamins with minerals at baseline. A secondary analysis considered use of multivitamins with minerals at a follow-up visit closest to the time of breast cancer diagnosis.

Investigators found that 2,239 participants were taking multivitamins with minerals at baseline and at the visit closest to breast cancer diagnosis, a subgroup defined as consistent users. The comparison group consisted of 3,358 participants who were consistent nonusers of multivitamins with minerals.

A comparison of consistent users and nonusers of multivitamins with minerals produced a hazard ratio of 0.70 for breast cancer mortality in favor of the consistent users. The difference translated into a 30% relative risk reduction (HR 0.70, 95% CI 0.55-0.91). The association persisted across multiple adjustments for potential confounders and in a propensity score-matched analysis (HR 0.76, 95% CI 0.60-0.96).

“The current findings of lower breast cancer mortality with multivitamins with minerals use in the largest number to date of breast cancer cases in postmenopausal women suggest possible benefit for multivitamin use in women diagnosed with invasive breast cancer,” the authors said in their discussion of the results.

“However, cautious interpretation is needed, especially for concurrent use during chemotherapy and radiation therapy. We do not have data on treatment of breast cancer in the cases and cannot comment on the potential interactions between multivitamins with minerals uses and breast cancer therapy in this study.”