New University of Otago research suggests the links between mental health and physical health may be deeper than previously documented.
The international study, headed by Otago behavioural scientist Dr Kate Scott, relies on data from the World Mental Health (WMH) survey.
Dr Scott, in collaboration with Harvard Medical School, looked at 47,000 WMH participants from 17 countries who had been assessed extensively for mental disorders, and were subsequently surveyed on their history of physical conditions.
Previous research had demonstrated links between psychotic disorders, such as schizophrenia, and physical disorders such as obesity and diabetes, Dr Scott said.
Depression had also been linked to heart disease.
But this study radically broadened the scope to include disorders such as depression, anxiety, substance abuse and others.
"What hasn't been clear is whether depression might be related to a much wider range of physical conditions, like lung disease and cancer,'' she said.
"And also whether other mental disorders - a wide range of anxiety disorders; alcohol and drug use disorders - are related to these chronic physical conditions in the same way.''
There were limitations to the study, Dr Scott said.
The data on participants' mental disorders was "very good'', but the data on their physical conditions was less than ideal.
It was based solely on participants reporting "whether or not a doctor had diagnosed them with a condition'', a measure that could leave room for error.
The study also looked at participants at one particular point in time, rather than checking in with them periodically over several years.
That, too, was less than ideal, Dr Scott said.
And the data gathered could not explain why mental and physical health seemed to be linked, although she said there was previous research that had identified three main mechanisms that might explain the connection.
The first was people's behaviour - people with certain mental health disorders might skew towards "worse health-related behaviour'', such as smoking, drinking and a poor diet, Dr Scott said.
The second involved the elevated stress levels associated with suffering from mental health issues - when stress hormones were "chronically elevated, it has negative physical consequences'', she said.
And the third was the healthcare system - doctors might pay less attention to patients' potential physical issues in favour of addressing mental health issues, which they might perceive to be more urgent.
However, that could send a patient's physical health on a downward spiral, Dr Scott said.
Those three mechanisms could indicate a path forward, she said.
Research into tweaking mental health treatment to account for those three mechanisms could go a long way to improving patients' physical health.
The next step was finding a way to do that research on a large scale - and fund it.
"Yes, it'd be very expensive,'' Dr Scott said.
