A surprising new study on advanced prostate cancer warns that high doses of multivitamins may increase cancer risk by a third. Study says the risk is only in association with aggressive cancer that has spread beyond the prostate. It finds an "increased risk of advanced and fatal prostate cancer among men who used multivitamins more than seven times a week, compared with men who did not use multivitamins. The association was strongest in men with a family history of prostate cancer and men who also took selenium, beta-carotene, or zinc supplements."
One big flaw in the study is lack of focus on which supplements could be the culprit. "Because multivitamin supplements consist of a combination of several vitamins and men using high levels of multivitamins were also more likely to take a variety of individual supplements, we were unable to identify or quantify individual components responsible for the associations that we observed."
Here's the reader's digest version: http://www.msnbc.msn.com/id/18681490/
Full report: Lawson KA, Wright ME, Subar A, Mouw T, Schatzkin A, Leitzmann MF. Multivitamin Use and Risk of Prostate Cancer in the National Institutes of Health -- AARP Diet and Health Study. J Natl Cancer Inst 2007; 99: 754-764