Differential mortality rates in late-life depression and subthreshold depression: 10-year follow-up in the community

Abstract

Background Although the association between depression and excess mortality is well-established, effects of subthreshold depression on mortality are unclear. We compared excess mortality between threshold and subthreshold depression, and investigated risks factors and disease-specific mortality rates according to the depression threshold levels. Methods Cross-sectional and longitudinal analyses of data from 1070 participants aged 55 and above of the Singapore Longitudinal Aging Study (SLAS). Baseline depression levels (Geriatric Mental State Examination, GMS), chronic medical comorbidity, instrumental activities of daily living (IADL) were related to baseline and 10-year follow-up of differential mortality rates according to depression threshold level. Results The prevalence of late-life subthreshold and threshold depression was 9.9% and 5.1%, respectively; 26.3% of respondents died by the 10-year follow-up, with a mortality rate of 28.2 per 1000 person-years. The risk of mortality increased with age, male gender, lower physical activity, multiple medical comorbidities and IADL-disability, but when stratified according to depression status, none of the variables was statistically significant for the subthreshold depression group. Depression, regardless of threshold levels, increased mortality risk by at least 1.6 folds, with small difference between the two. Cardiovascular mortality risk was significantly increased by 2.17 fold ( P =0.024) in threshold but not subthreshold depression. Conclusion Both subthreshold and threshold depression increase the risk of excess mortality, though it is slightly higher when reaches threshold levels. Subthreshold depression should be regarded as part of the depressive illness spectrum and more emphasis on recognition and timely treatment of this disorder should be considered in clinical practice.