Bayer is in the hot seat over claims that the antioxidant selenium in its One A Day Men’s Health Formula multivitamins may reduce prostate cancer risks. The Center for Science in the Public Interest sent a notification today to Bayer threatening to sue unless the company runs a new advertising campaign correcting claims it makes on product labels, about the “emerging research” on selenium. One such ad states “Along with your regular doctor checkups, switch to One A Day men’s. A complete multivitamin plus selenium, which emerging research suggests may reduce the risk of prostate cancer.”

In today’s announcement, the CSPI said the claim for One A Day supplements for men violates a consent decree the company signed with the FTC in 2007 in which the company paid a $3.2 million fine related to weight-loss claims made on behalf of One A Day multivitamin WeightSmart. At that time, Bayer also agreed not to make unsubstantiated claims in the future. Then there are the misleading ads for the birth control-pill Yaz that gloss over the serious health risks associated with the drug, and led to the FDA asking Bayer to run corrective advertising.

Last year, the trial results from the National Cancer Institute showed that selenium supplements did not reduce prostate cancer risks—and might actually cause harm in combination with vitamin E. The study also suggested a link between selenium and type 2 diabetes.