Imagine a medicine that reduced the death rate of breast cancer and risk of recurrent breast cancer by 50% lowered the risks of colon cancer and type 2 diabetes by two-thirds, and those of heart disease, hypertension, and Alzheimer’s’ disease by 40%. On top of that, it can be as effective as antidepressants or cognitive behavioral therapy in countering depression. That medicine exists, says Dr. Edward Laskowski of the Mayo Clinic: It’s’ called exercise. But…