Comorbidity is the occurrence of more than one condition/disorder at the same time, and is common among those with mental illness. It can involve more than one mental disorder, or one mental disorder and one or more physical conditions. People with multiple disorders are more disabled and consume more health resources than those with only one disorder.

This report provides a snapshot of the prevalence of mental illness in association with common chronic conditions in Australia in 2007. It compares the comorbidity group—comprising 12% of the population aged 16–85—with three other groupings:

  • people with a mental disorder but no physical condition
  • people with a physical condition but no mental disorder
  • people with no mental disorder or physical condition.

The results are all derived from the National Survey of Mental Health and Wellbeing 2007, conducted by the Australian Bureau of Statistics.

Main findings

Around one in nine Australians aged 16–85 had a mental disorder and a physical condition at the same time. These people were more likely to be female, and aged in their early forties.

The most common comorbidity was anxiety disorder combined with a physical condition, affecting around 1.4 million Australian adults. This was consistent for most age and sex groups, with the exception of younger males (aged 16–24) for whom substance use disorder combined with a physical condition was most common comorbidity.

In general, the results show that comorbidity increased with decreasing socioeconomic status (SES). For example, people living in the most disadvantaged areas of Australia were 65% more likely to have comorbidity than those living in the least disadvantaged areas.

Some health risk factors were more prevalent among people who had a mental disorder. For example, groups with a mental disorder had higher proportions of smokers compared with the groups without a mental disorder, and the comorbidity group had the highest proportion of smokers of all the groups.

People with a comorbidity of any mental disorder and physical condition had higher rates of hospitalisation than the three comparison groups. Similarly, the proportion of people consulting a health professional for a mental health disorder was much higher in the comorbidity group and mental disorder only group than the other comparison groups.

The coexistence of mental and physical conditions has an effect on quality of life. For example, on the Kessler Psychological Distress Scale 10, people in the comorbidity group were more than 10 times as likely to report high levels of psychological distress compared with the groups with no mental disorder.

People with comorbidity were around twice as likely as people without comorbidity to have more than 7 out of the past 30 days out of role (derived as the number of days totally unable to function plus half the number of days of reduced functioning).