A study in the American Journal of Clinical Nutrition (ACJN Mar 2010) reported a possible link between women who take multivitamins and breast cancer. The Swedish study looked at data from 35,000 women, ages 49 to 83, who took a multivitamin and were cancer-free at the beginning of a 10 year period. At the end of that 10 year period, the study concluded that older women who took a multivitamin were 19 percent more likely to develop breast cancer compared with women who did not take a vitamin.
But before you go throwing out your vitamins, there are important factors regarding this study that need to be considered. First, the study found only an association between multivitamins and breast cancer, NOT a cause and effect relationship – meaning that it cannot implicate vitamins as a cause of breast cancer. Secondly, the study did not look at the data on an individual basis. For this reason, researchers are not able to determine how one specific woman’s cancer risk might be increased if she takes a multivitamin.
So what do they think is the culprit in vitamins? The study goes on to discuss several different specific supplements such as calcium, vitamins A, E, etc in an attempt to clarify the results. It appears that folic acid ended up as the supplement of most interest. High doses of folic acid either from supplements or from fortified foods may be synthetic. Synthetic folic acid is more bioavailable in the body than folate from natural sources and this is what has been linked to having increased potential for cancer growth.
Those who are familiar with research know that there are just as many studies that were not able to show a link between multivitamins and cancer. Until further notice, you may just want to keep an eye on the amount of your folic acid intake. Many foods in the US have been fortified so you may be getting more than what is in your vitamins.
