Multivitamins & Breast Cancer: Headlines—But Not News
April 30, 2010 We received quite a few emails last week from women who were worried about news stories they heard linking multivitamins to breast cancer risk.
The news stories were generated by a study published in The American Journal of Clinical Nutrition which looked at multivitamin use and breast cancer incidence in 35,000 Swedish women and found that the women who took multivitamins were more likely to develop breast cancer than the women who did not.
As the best news stories pointed out, this study was an epidemiological study. This meant it could show that there was a correlation between multivitamin use and breast cancer risk, but it could not prove cause and effect. But as David Katz, MD, pointed out in his piece on Huffington Post, what very few reporters failed to point out was that this increased in risk was a statistic known as relative risk. As he clearly explained, the study found that the absolute risk of developing breast cancer for women who did not take multivitamins was about 0.26 percent, whereas for the women who did take multivitamins it was 0.32 percent. This does indeed result in a relative risk of 19 percent. But the absolute difference (0.32-0.26) is 0.06 percent. This means that the increased risk—if it is even real—is less than one-tenth of one percent.
And just as I was writing this, I saw a new headline, "Studies Clash On Vitamin Benefits." This article notes that a study done on women in Puerto Rico that was presented this week at the American Association for Cancer Research annual meeting found that women who took multivitamins and calcium supplements were at lower risk of developing breast cancer than women who did not take them.
This article had the best quote of all: "Both studies [the one done in Puerto Rico and the one done in Sweden] should be looked at in the broader context of research on the subject, which has consistently found no association between multivitamins and cancer," said Joanne Dorgan, epidemiologist at Fox Chase Cancer Center in Philadelphia, Pennsylvania."
Thank you, Joanne! If only the media would remember this each time a new study comes out about multivitamins and breast cancer.
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