People who are diagnosed with a major mental disorder are at greater risk of being diagnosed with another, according to a new Danish study published in the journal JAMA Psychiatry.

For the first time, researchers looked at the risks of double diagnosis (comorbidity) within ten major groups of mental disorders. Based on register data from 5.9 million people living in Denmark from 2000 to 2016, the study is the most detailed study of comorbidity ever conducted in the field of mental health.

“We knew from previous smaller studies that some types of disorder tended to occur together. But now we can confirm that comorbidity is the rule, not the exception,” says Oleguer Plana-Ripoll, postdoctoral researcher at the National Centre for Register-based Research at Aarhus Business and Social Sciences (BSS) in Denmark and the main author of the study.

“Those who receive a diagnosis of a specific major mental disorder are more likely to receive diagnoses for all other types of mental disorders.”

Due to the study’s size, the researchers were able to measure the absolute risks of people developing more than one mental disorder later in life and also uncover how different types of mental disorders can accumulate across a lifespan.

“This is the first study to provide a comprehensive description of all possible associations between pairs of mental disorders using national registers available for a whole population,” says Plana-Ripoll.

The findings reveal that people who are diagnosed with one mental disorder are not only more likely to be diagnosed with other mental disorders, but also that this risk persists for many years after the first diagnosis.

“We have provided the field with fine-grain details — for example that the risk of developing more than one mental disorder is not constant over time,” says Oleguer Plana-Ripoll.

The researchers also developed an interactive webpage that allows professionals and the general public to look up the risks of double diagnoses according to age, sex and type of mental disorder.

“We want to ‘democratize’ the results so that they are more widely understood by clinicians and people with mental disorders and their caregivers,” says Professor John McGrath, head of the Niels Bohr Professorship research program at Aarhus University.

“We hope that this new information will help the clinicians to monitor the development of mental disorders. This is especially important for people who develop a mental disorder when they are young.”

Source: Aarhus University