I've heard from various sources they may be linked to alzheimer's. Wow, cast iron is what I use for most of my cooking. 
examine.com
Are cast iron pans unsafe? - Examine
Too much iron has been linked to a wide variety of conditions, such as Alzheimer’s, heart disease, and colorectal cancer to name just a few.[5][6][7] There’s a couple groups of people who don’t have to worry quite as much about iron overload though: menstruating women and vegetarians/vegans. But for others, especially those who regularly eat red meat, it doesn’t take much to push yourself into excess iron territory.