Physical illness accumulates early and quickly in people with severe mental illness

People living with schizophrenia-spectrum or bipolar disorder (collectively referred to as severe mental illness) have a life expectancy more than 10 years shorter than that of the general population, largely driven by preventable physical disease as opposed to suicide alone. Research and clinical care have traditionally focused on cardiometabolic disease, but people with severe mental illness carry an elevated burden of chronic disease across most organ systems. Through a systematic review and meta-analysis, we previously estimated around one in four people with severe mental illness have physical multimorbidity (two or more co-occurring chronic physical conditions), roughly 2.4 times the odds of people without severe mental illness. What has been missing is longitudinal evidence on how quickly this disease burden accumulates relative to the general population. Without that picture, it's hard to know when prevention efforts are best targeted.

Measuring physical illness and mental illness

Using linked Queensland Health hospital admission, emergency department and mortality data spanning 2000-2023, we identified 30,189 people with a hospital-recorded diagnosis of severe mental illness and compared them to 148,476 age- and sex-matched hospital comparators without these diagnoses. We grouped chronic physical disease diagnoses into eleven systems: cardiovascular, endocrine, gastrointestinal, genitourinary, haematological, chronic infectious, malignancy, musculoskeletal, neurological, respiratory, and combined ophthalmic and ear-nose-throat group. We used competing-risk survival methods to estimate how quickly people accumulated disease across one, two, three, four, and five or more of these systems over up to 20 years of follow-up, while accounting for this cohort's substantially higher risk of death before physical disease could develop.

What we found

People with severe mental illness had a substantially higher incidence of chronic physical disease than matched comparators, and the relative gap widened with each additional system involved. The relative incidence was close to double for developing a chronic physical disease in at least one system (adjusted hazard ratio 1.85), rising to more than three times that of comparators for physical multimorbidity across five or more systems (adjusted hazard ratio 3.16). In absolute terms, by 20 years there were almost 18 additional cases of physical multimorbidity (at least two systems) per 100 people with severe mental illness, and close to 12 additional cases affecting five or more systems. Ten of the eleven systems examined showed significantly elevated incidence, led by endocrine disease (hazard ratio 3.52); cancer was the only system where incidence did not differ significantly from comparators. The relative gap was largest in people younger than 25, particularly young women, who had more than nine times the rate of developing physical multimorbidity across five or more systems compared with their matched peers (full results are published in The Lancet Psychiatry).

What needs to happen next

These findings show that physical multimorbidity in severe mental illness starts to accumulate well before most chronic disease screening begins; for example, cardiovascular screening is not recommended until 45, or 35 for those with diabetes and 30 for First Nations peoples. Given the widest relative gap was in people younger than 25, we believe assertive prevention and treatment of physical disease need to start at a much younger age.

Australia's mental health and physical health systems remain largely siloed, and most chronic physical disease screening tools were never designed for young people living with severe mental illness. Emerging prediction tools such as the Psychosis Metabolic Risk Calculator, and the structured lifestyle and pharmacological treatment recommendations made in the recent Lancet Psychiatry Physical Health Commission reports offer a starting point. But these holistic care models will only make a difference if they are embedded into health services.

We would like to see dedicated investment in integrated physical health screening from the point of first contact with mental health services, particularly for young people with severe mental illness, alongside support for modifiable risk factors such as smoking and medication-related physical health impacts. Cancer screening in this population also deserves scrutiny, given known underdiagnosis and higher mortality rates, despite the comparatively modest incidence signal in our data. Given that the onset of severe mental illness occurs most commonly during youth, health services and policymakers have a real opportunity to prevent, not just treat, a lifetime of accumulating physical illness.

Conclusion

People in Queensland with schizophrenia-spectrum or bipolar disorder accumulate physical multimorbidity across multiple systems earlier and faster than their peers, with the disparity starkest amongst young people. Closing this gap will require models of care that treat physical and mental health together from the time of first contact with services, rather than decades later once multimorbidity has already developed.

Sean Halstead is a psychiatry registrar and PhD candidate (University of Queensland) based in Brisbane. He is also a Research Ambassador with Equally Well Australia.

Dan Siskind is a psychiatrist and Professor of Psychiatry at the University of Queensland. He works clinically at Metro South Addiction and Mental Health Services in Brisbane.

SH declares no conflicts of interest. DS serves on the Viatris Australian Clozapine Quality Advisory Committee and the Douglas ANZ Clozapine Assurance Committee, and has received speaker and/or consultancy fees from Servier, Otsuka, Viatris, Douglas, Teva, Phebra, and Lundbeck.