Causation?

According to a new study released today, heavy multivitamin use may be linked to advanced prostate cancer. The study found "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. "

But as the Prostate Cancer Foundation indicates, there has been ongoing debate as to whether these very supplements (selenium, beta-carotene, and zinc) might actually decrease prostate cancer risk. My guess is that the guys in this study that were taking these supplements did so precisely because they perceived (and acted on) an increased risk of prostate cancer not captured by the screen. Thus, the very vitamins and minerals extolled as beneficial come to look like carcinogens.