The long-term outcome of subthreshold depression in later life.

BACKGROUND: Subthreshold depression (SUBD) in later life is common and important as prodromal state and prominent risk factor in the development of major depressive disorder (MDD). Indicated prevention can reduce the incidence of MDD among people with SUBD substantially, but needs to be targeted to those that are truly at risk of developing MDD.

METHOD: N = 341 eligible participants with SUBD were included from the first (1992/1993), second (1995/1996) and third (1998/1999) cycle from the Longitudinal Aging Study Amsterdam (LASA) by using a two-stage screening design. LASA is an ongoing prospective cohort study in The Netherlands among the older population (55-85 years). At baseline (1992/1993) N = 3107 participants were interviewed and follow-up cycles were conducted every 3 years until 2008/2009, resulting in maximal 17 years of observational period. The proportion of people that developed MDD, remained SUBD, or recovered from SUBD was measured and Cox proportional regression analyses were performed to investigate 29 putative predictors of MDD and recovery from SUBD.

RESULTS: N = 153 (44.9%) recovered from SUBD, N = 138 (40.5%) remained chronically SUBD, and N = 50 (14.7%) developed MDD (incidence rate 15.1/1000 person-years). Women, high neuroticism, more chronic diseases, high body mass index, smoking and less social support predicted conversion to MDD. Men, low neuroticism and absence of pain predicted recovery from SUBD.

CONCLUSIONS: Although older people with SUBD are clearly at risk of developing MDD, the majority did not, even after a long and thorough follow-up. Given the risk factors that were uncovered, targeting and prevention of MDD in those at very high risk is feasible.