The role of frailty in the association between depression and somatic comorbidity: Results from baseline data of an ongoing prospective cohort study

BackgroundDepression and physical frailty in older persons are both associated with somatic diseases, but are hardly examined in concert.ObjectivesTo examine whether depression and physical frailty act independently and/or synergistically in their association with somatic diseases.DesignBaseline data of an ongoing observational cohort study including depressed cases and non-depressed comparison subjects.SettingsNetherlands Study of Depression in Older persons (NESDO).Participants378 depressed older persons confirmed by the Composite International Diagnostic Interview (CIDI), version 2.1, and 132 non-depressed comparison subjects.MethodsMultiple linear regression analyses adjusted for socio-demographic and life-style characteristics were conducted with the number of somatic diseases as the dependent variable and depression and physical frailty as independent variables. Physical frailty was defined as ≥3 of the following characteristics, slowness, low physical activity, weight loss, exhaustion, and weakness.ResultsDepression and physical frailty did not interact in explaining variance in the number of somatic diseases (p = .57). Physical frailty, however, partly mediated the association between depression and somatic diseases, as the strength of this association decreased by over 10% when frailty was added to the model (B = 0.47, p = .003, versus B = 0.41, p = .01). The mediation effect was primarily driven by the frailty criterion exhaustion. Of the remaining frailty components, only slowness was associated with the number of somatic diseases; but this association was fully independent of depression.ConclusionsOur results suggest that depression and physical frailty have common pathways towards somatic diseases, as well as unique pathways. As no high-risk group was identified (no significant interaction), mental health nurses should regularly monitor for physical frailty within their caseload of depressed patients.