Using a life-course approach to better understand depression in older age

This doctoral thesis aimed to explore the prevalence of depression, and to identify risk factors, secular changes, and consequences of depression in late adulthood from a life-course perspective. The four studies in this thesis were based on data from the H-70 study, the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K), and the Kungsholmen Project (KP). The major findings of these studies are summarized below. Study I. This study used five-year follow-up data from the H-70 study to examine whether the association between social factors and depression has changed between the 1970s and 2000s in two birth cohorts of septuagenarians. Feelings of loneliness were related to higher depression risk in both of the cohorts. However, infrequent visits with others than children or neighbors (once per month or less), and the perception of having too little contact with others, were related to an increased risk of depression in 75-year-olds examined in the 1970s, but not in those examined in the 2000s. Study II. This study used SNAC-K data to examine to what extent the prevalence of depression varies when using different depression definitions and sub-samples of the population of adults aged 60−104 years. The prevalence of any depression ranged between 4.2% to 9.3% according to the diagnostic criteria (DSM-IV-TR and ICD-10); 9.2% to 10.6% for the rating scales (MADRS and GDS15); and was 9.1% for self-report. Depression prevalence was lower when excluding those having dementia, as compared to the total population. Moreover, being physically dependent or not having a partner were related to higher depression prevalence across the majority of the depression definitions. Study III. This study used nine-year follow-up data from SNAC-K and KP to explore whether low mood was related to an increased risk of dementia in two birth cohorts of adults above 70 years of age, and whether marital status and living situation modify this relationship. Those having low mood at baseline were at an increased risk of dementia in both cohorts combined (hazard ratio [HR] 1.2, 95% confidence interval [CI] 1.0-1.4), compared to those without low mood. However, the higher risk was detected only in those who did not have a partner (HR 1.5, 95% CI 1.2-1.9), or lived alone (HR 1.5, 95% CI 1.2-1.9), but not among those who had a partner or lived with someone (HR 0.8, 95% CI 0.51.2). Study IV. This study used six-year follow-up data from SNAC-K to explore whether the experience of negative life events across the life span was related to an increased depression risk later in life. The total number of negative life events was associated with an increased risk of any depression. When further examining timing of the events, the experience of negative events (≥90 th percentile) in early(0−18 years, odds ratio [OR] 2.4, 95% CI 1.2-5.0) or late-life (>65 years, OR 2.1, 95% CI 1.1-4.4) were associated with an increased risk of any depression, but not those occurring in early-adulthood (19−40 years, OR 1.4, 95% CI 0.7-2.7) or middle-adulthood (41−65 years, OR 1.3, 95% CI 0.6-3.1). Conclusions. Depression prevalence was similar independent of the depression definitions used, except for ICD-10, showing much lower prevalence. Moreover, the quantity and quality of social contacts with others were related to depression in older adults examined in the 1970s, but not in those examined 30 years later. In addition, marital status and living situation have the possibility to buffer the detrimental effects of low mood on dementia onset. Finally, there are critical time periods in earlylife (0−18 years) and late-life (>65 years), when the experience of negative life events exacerbates depression risk in later life.