For centuries, mental illness and physical illness have been considered two distinct categories, each with its own field of study, its own doctors, and its own menu of treatments.
A new study from the University of Colorado Boulder challenges this long-standing dichotomy, showing that the same chunks of DNA that underlie mental illnesses such as depression, PTSD, and ADHD are also linked to risk for many physical illnesses.
Research involving approximately 2 million people published in journal nature communicationsreveals how often and why mental and physical illness occur. This could ultimately pave the way for new treatments that address both, the authors said.
The surprising finding here is not that mental and medical illnesses are related, but rather how closely they are related. At the genetic level, we found that there was so much overlap that it wasn’t actually two completely different types of disease. ”
Andrew Grotzinger, senior author, assistant professor of psychology and neuroscience
Diseases occur in pairs
Grotzinger’s previous research has shown that people with one mental illness often have many (41% meet criteria for four or more), possibly due to common genetic factors. Physical disabilities also have groups, with 38% of the world’s population living with two or more chronic conditions.
Only recently have scientists begun to investigate how often physical and mental illnesses coincide. A recent study examining the medical records of the Danish population found that having a mental illness increases the risk of physical illness by 37%, and that some mental illnesses increase the risk of some physical illnesses by nearly 400%. Studies have shown that people with depression are 1.5 times more likely to develop heart disease than people without depression.
“In the clinic, you rarely see someone walk into the room with just one symptom,” said lead author Jeremy Lawrence, a doctoral student in clinical psychology. “If we can better understand the crosstalk between these symptoms, we will be able to better help the patient as a whole.”
To determine how common these body-mind combinations are, Grotzinger and Lawrence analyzed genetic material and health information from 1.9 million people.
Researchers looked at which parts of DNA were associated with 73 physical outcomes across eight medical areas: neurological, respiratory, circulatory, digestive, endocrine/metabolic, genitourinary, musculoskeletal, and cancer. They then did the same for 13 psychiatric disorders across five categories: obsessive-compulsive disorder, psychotic/thoughts, neurodevelopmental disorders, internalizing disorders, and substance abuse.
When comparing physical and mental disorders, genetic risk factors overlapped 42% of the time.
“At the genetic level, we found that the shared risks between psychiatric and non-psychiatric diseases are widespread and substantial,” Lawrence said.
Neurodevelopmental disorders like ADHD were most likely to be associated with physical illness. Genetically, ADHD has more in common with physical illnesses than with other mental illnesses.
Major depression, PTSD, and substance use disorders also had high levels of shared risk with physical illness. In contrast, obsessive-compulsive disorders such as obsessive-compulsive disorder and Tourette syndrome are rarely associated with physical illness and appear to have a protective effect when it comes to gastrointestinal disorders.
Some specific diseases tend to co-occur.
For example, schizophrenia tends to be combined with gastrointestinal problems. Bipolar disorder tends to coexist with genitourinary disorders and sleep disorders. Depression and anxiety tend to co-exist with cardiovascular disease.
Chicken or egg?
Lawrence pointed out that having a mental illness such as depression can lead to behaviors that lead to poor physical health, such as poor eating habits and a sedentary lifestyle. A physical illness, such as a cancer diagnosis, can also increase the risk of mental illness, such as depression. In some cases, common parts of DNA can independently increase the risk of both physical and mental illnesses.
Lawrence envisions a day when treatments will be developed that achieve both physical and mental health goals at the same time.
He cited GLP-1 agonists, originally developed for diabetes, then prescribed for weight loss, and now showing promise for use in substance abuse disorders, as an example of how drugs targeting physical illnesses are making inroads into the mental health field.
Genetics can also be used to predict which groups of diseases on the mental and physical spectrum a person is susceptible to, allowing for early intervention.
Grotzinger said that for now, research shows that addressing mental illness can go a long way toward improving overall health. It could also help break down the silos between psychology and general medicine.
“You can spit into a tube or have someone put a blood pressure cuff on you to diagnose a physical illness, but in many ways we don’t have those tools for mental illness, which is why some people think of mental illness as more esoteric and less specific,” Grotzinger said. “Mental illness is just as real as any other medical illness, and our findings help support that claim.”
sauce:
University of Colorado Boulder
Reference magazines:
Lawrence, J.M.; others. (2026). Genetic responsibility shared across mental and physical disease systems. nature communications. DOI: 10.1038/s41467-026-69218-1. https://www.nature.com/articles/s41467-026-69218-1
