The Reciprocal Relationship Between Disability and Depression

An important question for both clinical research and practice is whether favorable psychological attributes slow the progression of disability in older people, or conversely, whether adverse psychological attributes speed disability's progress. Cross-sectional research has established associations between affective data and disability in older people,1 and longitudinal analysis has documented both the significant predictive value of initial depression for subsequent physical performance declines and synchrony between depression and disability self-reports in changes over time.2,3 A seminal article by Turner and Noh used path analysis of 4-year panel data to document that increased disability was a significant factor explaining increased symptoms of depression.4 However, without contradicting any reciprocal causal elements in the relationship between disability and depression, the particular importance of depression in regard to functional health has been emphasized repeatedly by Ormel and colleagues3, including Kempen and others5,6 whose data reliably support the conclusion that traditional ADL and IADL functional health self-report data are highly susceptible to the effects of depression. Other research has established that the associations between depression and disability are even stronger than those seemingly inevitable associations between disability and the presence of major chronic medical conditions that cause physical deterioration.7,8 In this issue of the Journal, Oslin et al. report further research on associations between disability and depression in older adults.9 Comparing admission data with 3-month post-discharge data following inpatient hospitalization for treatment of depression, the investigators found substantially decreased depressive symptoms and overall increased instrumental ADL and health-related quality of life. These findings are as expected for patients receiving effective treatment for depression, and they provide an important research context for further examination of within-subject longitudinal relationships between changes in disability and change in depression. The article's inferential data analysis, estimating the magnitudes and reproducibility of these longitudinal relationships, documented significant associations between changes in depression symptoms and changes in ADL, IADL, and in most health-related quality of life data. Thus, regarding the primary research hypothesis of the study, associations between improvement in depression and improvements in disability data were both statistically reliable and, particularly when examined in observer/collateral contact data – usually from spouse or children – also documented clinically significant effect sizes showing parallel changes in relief from both depression and disability. There were similar findings for all eight non-ADL health-related quality of life indicators in relation to depression in the study. All eight improved quality of life findings were unequivocally statistically reliable and clinically substantial. Included here were findings of improvements in health perception, physical health, mental health, role emotional functioning, role physical functioning, pain, social functioning, and energy/fatigue data, all paralleling improvement in depression. Indeed, some of the improvements in health-related quality of life in association with decreased depression were even stronger than the improvements reported for the ADL and IADL data. For example, partial correlation analysis found that changes in depression accounted for a surprisingly large 12% of variance in changes in observer-reported health perception of patients, after controlling for the patient's age, comorbidities, gender, and cognitive ability. Studies of adult populations find that both disability and depression are commonplace in older people. Relationships between processes of aging, disability, and depression are complex, and definitive knowledge about this nexus is both dear and difficult to ascertain. However, in accordance with evidence presented by Oslin and colleagues,9 there can be little room for doubt that appropriate treatment for symptoms of depression in older patients can reverse excess disability and improve health-related quality of life. The reciprocal relationship between depression and disability was aptly described by Bruce and colleagues.10 Regardless of whether declines are first triggered by adverse psychological perturbations or by adverse functional ability challenges, treatment of either frank depression or of subclinical depression symptoms has the potential to relieve or reverse substantially a destructive spiraling decline of disability-depression reciprocity in cause and effect.10, p. 1798 Accordingly, Oslin and colleagues' conclusion that “depression leads to excess disability that is reversible” via treatment for depression is a valid call for attention to psychological symptoms of depression in health care for the prevention or relief of disability in older people.9