Many people take multivitamin with mineral supplements ("multivitamins") as part of a strategy to maintain or improve overall health. Such supplements typically include micronutrients at levels that are at least high enough to prevent deficiencies in them. Generally speaking, studies have reported little or no effect of multivitamin use on mortality in the general population. However, a few studies have suggested that taking multivitamins might be beneficial for breast cancer survivors, possibly because breast cancer treatment and cancer itself can lead to the depletion of some important vitamins and minerals. Now a major new prospective U.S. study has reported that postmenopausal breast cancer survivors using multivitamins are less likely to die from breast cancer than non-users.

Multivitamin use is not linked to lower breast cancer risk

Most studies have found no association between multivitamin use and risk of breast cancer. A 2011 meta-analysis of previous studies concluded that multivitamin use was not likely to be associated with a significantly higher or lower risk of breast cancer. On the other hand, a 2010 Swedish prospective study reported that multivitamin use was associated with increased risk of breast cancer.

Essential vitamins and minerals are necessary for cancer prevention, but can sometimes promote cancer at high levels. In other words, supplementation might prevent breast cancer in women who are deficient in a given micronutrient, whereas the same supplement could promote it in women who are not deficient, especially if taken in high doses or a chemical form that is not commonly found in nature. Excessive levels of copper, folic acid, iron, selenium, vitamin A, vitamin C, vitamin E, and zinc all have been linked to increased risk of breast cancer. The relationship between breast cancer and these micronutrients can be quite complex. For example, zinc appears to help prevent the development of breast cancer while possibly facilitating the growth of existing tumors. Therefore, when it comes to taking multivitamins, more is not necessarily better.

Latest research links multivitamins use to lower risk of breast cancer-specific death

The prospective study referenced at the beginning of this news article was designed to investigate whether taking multivitamins with minerals ("multivitamins") influences breast cancer-specific survival in postmenopausal women with invasive breast cancer. The study included 7,728 U.S. women aged 50 to 79 upon enrollment in the Women’s Health Initiative, a large trial conducted using 40 clinical sites. The women were followed for an average of 7.1 years after diagnosis. Use of multivitamins was assessed at the baseline intake interview and subsequently at the visit nearest to the diagnosis of breast cancer. Approximately 38% of the women reported multivitamin use at baseline.

A total of 6.7% (518) of the study participants died from breast cancer during follow up. Breast cancer-specific mortality was found to be 30% lower among multivitamin users compared to non-users, after controlling for multiple variables also known to influence prognosis, including alcohol use, level of physical activity, body weight, education level, race/ethnicity, age at diagnosis, and the presence of smoking, depression, or diabetes. The authors conclude that postmenopausal breast cancer patients using multivitamins had lower risk of breast cancer-specific death than non-users. The authors comment that the findings require confirmation.

Please see our article on multivitamin use and breast cancer for more information.