Multivitamin use linked to increased risk of breast cancer, study says

Swedish researchers have found a link between multivitamin use and an increased risk of breast cancer in a study of more than 35,000 middle aged and older women. Scientists working on the study are concerned and believe more research is needed.

In 1997, scientists at the Karolinska Institutet in Stockholm, Sweden asked women to complete a health questionnaire, examining closely what they called “breast cancer risk factors.” At the time, all 35,329 women were cancer-free. In the follow up ten years later, 974 of these women were diagnosed with incident breast cancer, 293 of whom were taking multivitamins. According to the study, these findings show a 19 percent increased risk in breast cancer (after taking out lifestyle factors like exercise, weight, diet, smoking and family history).

“Many women use multivitamins in the belief that these supplements will prevent chronic diseases such as cancer and cardiovascular disease,” Susanna Larsson, MD, professor of the Division of Nutritional Epidemiology, said in the report on the findings. “However, whether the use of multivitamins affects the risk of breast cancer is unclear.”

Other studies done in the U.S. contest the Swedish institute’s findings. In a 2009 prospective study done by researchers at Harvard and the Tokyo Women’s Medical University, multivitamin use was not found to be associated with the “overall risk of breast cancer.” Instead, it found taking multivitamins regularly might reduce the risk for women consuming alcohol and decrease the risk of certain types of breast cancer for all women.

Larsson pointed out to Reuters Health other reasons could have led to the increased cancer risk. The study might not have examined certain factors that led to these results, or B vitamin folic acid, which commonly gives different results in health studies, is skewing the findings. As multivitamins contain a variety of nutrients, it is hard to pinpoint which mineral or vitamin is causing these results, according to Larsson.

Currently, 28 percent of Americans take a multivitamin regularly, according to the Council on Responsible Nutrition. The Journal of American Medical Association strongly recommends all Americans supplement with a multivitamin. Sales of the supplement are also rising, showing a consumer attachment to multivitamins, according to a 2008 report by Nutrition Business Journal. NBJ reported sales of multivitamins were worth $4.7 billion in 2008, with 4.3 percent growth expected over three years.

UPDATE: CRN reports the findings from this study are confusing and need further review to understand what this means to consumers and retailers.

Andrew Shao, senior vice president, scientific and regulatory affairs, CRN:
“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. More research is definitely needed to sort out the conflicting data. In the meantime, the message to consumers is still the same: it is better to meet your nutrient needs than not, and a simple, affordable daily multivitamin helps us all to achieve that. This study does not change that.”