title: Coexisting medical comorbidity and depression: multiplicative effects on health outcomes in older adults.
abstract: BACKGROUND
  Depression in the elderly is often associated with coexisting medical illnesses. We investigated the individual and combined impacts of depression and medical illnesses on disability and quality of life among community-living older persons.
  
  
  METHODS
  Cross-sectional and longitudinal analyses of data from 1,844 participants aged 55 and above of the Singapore Longitudinal Aging Study (SLAS-1). Baseline depressive symptoms (Geriatric Depressive Scale, GDS≥5) and chronic medical comorbidity (≥2) from self-reports were related to baseline and 2-year follow up instrumental and basic activities of daily living (IADL-BADL), and quality of life (Medical Outcomes Study 12-item Short Form (SF-12) physical component summary (PCS) and mental component summary (MCS) scores.
  
  
  RESULTS
  The prevalence of depressive symptoms was 11.4%. In main effect analyses of cross-sectional and longitudinal relationships, depression and medical comorbidity were individually associated with higher risk of IADL-BADL disability and lower PCS and MCS scores of quality of life, and only medical comorbidity was associated with increased risk of hospitalization. Significant interactive effects of depression and medical comorbidity were observed in longitudinal relationships with IADL-BADL disability (p = 0.03), PCS (p < 0.01), and MCS (p < 0.01) scores at follow up. The associations of medical comorbidity with increased odds of IADL-BADL disability and decreased SF-12 PCS and MCS scores were at least threefolds stronger among depressed than nondepressed individuals.
  
  
  CONCLUSIONS
  Medical comorbidities and depression exert additive and multiplicative effects on functional disability and quality of life. The adverse impact and potential treatment benefits of coexisting mental and physical conditions should be seriously considered in clinical practice.
authors.affiliation: Gerontology Research Programme and Department of Psychological Medicine, Yong Loo Lin School of Medicine,National University of Singapore,Singapore.
authors.forename: Cyrus Sh
authors.initials: CSh
authors.lastname: Ho
authors.affiliation: Gerontology Research Programme and Department of Psychological Medicine, Yong Loo Lin School of Medicine,National University of Singapore,Singapore.
authors.forename: Liang
authors.initials: L
authors.lastname: Feng
authors.affiliation: Gerontology Research Programme and Department of Psychological Medicine, Yong Loo Lin School of Medicine,National University of Singapore,Singapore.
authors.forename: Johnson
authors.initials: J
authors.lastname: Fam
authors.affiliation: Gerontology Research Programme and Department of Psychological Medicine, Yong Loo Lin School of Medicine,National University of Singapore,Singapore.
authors.forename: Rathi
authors.initials: R
authors.lastname: Mahendran
authors.affiliation: Gerontology Research Programme and Department of Psychological Medicine, Yong Loo Lin School of Medicine,National University of Singapore,Singapore.
authors.forename: Ee Heok
authors.initials: EH
authors.lastname: Kua
authors.affiliation: Gerontology Research Programme and Department of Psychological Medicine, Yong Loo Lin School of Medicine,National University of Singapore,Singapore.
authors.forename: Tze Pin
authors.initials: TP
authors.lastname: Ng
mesh_terms: D000203:Activities of Daily Living / Q000523:psychology; D000368:Aged / Q000523:psychology / Q000706:statistics & numerical data; D002908:Chronic Disease / Q000453:epidemiology / Q000523:psychology; D015897:Comorbidity; D003430:Cross-Sectional Studies; D003863:Depression / Q000453:epidemiology*; D006233:Persons with Disabilities / Q000523:psychology / Q000706:statistics & numerical data; D005260:Female; D006304:Health Status; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015995:Prevalence; D011569:Psychiatric Status Rating Scales; D011788:Quality of Life; D012307:Risk Factors; D012846:Singapore / Q000453:epidemiology