Multivitamins and breast cancer link?

The study, reported in the American Journal of Clinical Nutrition, points only to an association between multivitamin use and breast cancer. It does not prove that the supplements directly contribute to the disease. The findings come from a decade-long study of more than 35,000 Swedish women who were between the ages of 49 and 83 and cancer-free at the outset. Over an average of 10 years, 974 women were diagnosed with breast cancer. Researchers found that women who reported multivitamin use at the study's start were 19 percent more likely than non-users to develop breast cancer. Still, the large majority of multivitamin users did not develop breast cancer during the study period. Of 9,017 users, 293 were diagnosed with the disease, as were 681 women among the 26,000-plus who did not use multivitamins. And while the study points to a generally higher risk of breast cancer among multivitamin users as a whole, the risks to any individual woman would likely be small.

Alternatively, a recent study of more than 160,000 older U.S. women found that over eight years, those who took multivitamins were no less likely than non-users to die of heart disease or cancer, with all cancers lumped together in a group.

Bonnie - as observational studies go, this one appears to have been well-done overall. It was a large, prospective cohort of more than 35,000 women who were healthy at baseline and followed for almost 10 years. The finding of an increased risk of breast cancer is puzzling, and in direct conflict with other similarly designed studies such as the well-regarded Nurses Health Study out of Harvard, which showed just the opposite—that multivitamin use was associated with a significant decrease in breast cancer risk. And there are a few other studies that show ‘no effect.' So it is difficult to say what this study means on its own. To their credit, the authors are balanced in their discussion of the findings and are careful not to draw firm conclusions from this one study.

Based upon the wealth of data on multivitamins in research and in my own clinical setting, my opinion has not changed one iota. They are a crucial part of any healthy lifestyle.