Mental health is physical health. A study of 5.9 million people in Denmark found that people diagnosed with a mental illness were more likely to later develop physical diseases, in 76 of the 90 combinations researchers checked. Researchers at Aarhus University used Denmark's national health records for everyone born in the country between 1900 and 2015, and followed them from 2000 to 2016. About 1 in 9 people, nearly 700,000, were diagnosed with a mental disorder. The study was published in the New England Journal of Medicine in 2020. Ten types of mental illness were compared with 9 types of physical disease, such as heart disease, cancer, and lung problems. In 76 of the 90 pairs, people with the mental illness were more likely to develop the physical disease afterward. The typical increase was 37 percent. Eating disorders showed the biggest jump, with about 3.6 times the risk of urinary and reproductive organ problems. Within 15 years of a diagnosis, the risk of a physical disease ranged from under 1 percent for one pairing to 54 percent for heart and blood vessel disease among people with brain-based disorders such as dementia. A few pairs showed lower risk, like schizophrenia and bone and muscle problems. Medication side effects, habits like smoking, fewer doctor visits, and shared biology could all play a part, and the study can't separate them. Across nearly 6 million people, a mental health diagnosis came with higher physical health risk in 76 out of 90 comparisons.