For centuries, mental illness and physical disease have been viewed as two distinct categories, each with its own field of study, its own doctors, and its own menu of treatments. New CU Boulder research calls that age-old dichotomy into question, showing that the same chunks of DNA that underly psychiatric disorders like depression, PTSD and ADHD are associated with risk of a host of physical ailments, too. The study of nearly two million people, published in the journal Nature Communications, sheds light on just how often, and why, psychiatric and physical diseases go hand in hand. It could ultimately pave the way for new therapies that address both, the authors said.