The relationship between physical ill-health and mental ill-health in adults with intellectual disabilities

Background: People with intellectual disabilities face a much greater burden and earlier onset of physical and mental ill-health than the general adult population. Physical-mental comorbidity has been shown to result in poorer outcomes in the general population, but little is known about this relationship in adults with intellectual disabilities.

Aims: To identify whether physical ill-health is associated with mental ill-health in adults with intellectual disabilities and whether the extent of physical multi-morbidity can predict the likelihood of mental ill-health. To identify any associations between types of physical ill-health and mental ill-health.

Method: A total of 1023 adults with intellectual disabilities underwent comprehensive health assessments. Binary logistic regressions were undertaken to establish any association between the independent variables: total number of physical health conditions, physical conditions by International Classification of Disease-10 chapter and specific physical health conditions; and the dependent variables: problem behaviours, mental disorders of any type. All regressions were adjusted for age, gender, level of intellectual disabilities, living arrangements, neighbourhood deprivation and Down syndrome.

Results: The extent of physical multi-morbidity was not associated with mental ill-health in adults with intellectual disabilities as only 0.8% of the sample had no physical conditions. Endocrine disease increased the risk of problem behaviours [odds ratio (OR): 1.22, 95% confidence interval (CI): 1.02-1.47], respiratory disease reduced the risk of problem behaviours (OR: 0.73, 95% CI: 0.54-0.99) and mental ill-health of any type (OR: 0.73, 95% CI: 0.58-0.92), and musculoskeletal disease reduced the risk of mental ill-health of any type (OR: 0.84, 95% CI: 0.73-0.98). Ischaemic heart disease increased the risk of problem behaviours approximately threefold (OR: 3.29, 95% CI: 1.02-10.60).

Conclusions: The extent of physical multi-morbidity in the population with intellectual disabilities is overwhelming, such that associations are not found with mental ill-health. Mental health interventions and preventative measures are essential for the entire population with intellectual disabilities and should not be focussed on subgroups based on overall health burden.