Perhaps the better question is, why are mental disorders on the rise. Understand that this is not an American anomaly, it is world wide. Side affects of a lot of things perhaps. Air polution, pesticides, herbicides, insecticides, contaminated water. Obesity is on the rise, diabetes is almost epidemic and a host of other diseases. I don't know why, but I do know it is happening, Is it our food supply? Perhaps, but if all these things are happening to our bodies, why do we think it isn't happening to our minds?