Groffen et al. [6] recently conducted an investigation among a sample of 4,809 participants from the Reykjavik Study (aged 66–93 years). Similar to the findings presented by Vink and colleagues [3], education level was related to depression risk: participants with lower education levels were more likely to report depressed mood in late-life than those with a college education (odds ratio [OR] = 1.87, 95 % confidence interval [CI] = 1.35–2.58). Kim and Durden [7] found that having a college degree was associated with lower levels of depressive symptoms in all age groups, including older adults (p < 0.001).

Socioeconomic status (SES) variables have also been recognized as significant predictors: Results from a meta-analysis by Lorant and colleagues [8] showed that lower SES individuals had a greater odds of developing depression than those in the highest SES group (OR = 1.24, p = 0.004); however, the studies involved in this review did not focus on older populations. Kim and Durden [7] observed that the association between income level and depressive symptoms was not consistent across age groups: among individuals aged 65 and older, no difference in the change in depression scores over time was found between the low- and high-income groups. In the Reykjavik Study [6], lack of car ownership in midlife and history of early-life food shortages were associated with incident depressed mood in later life.

While Lyness and colleagues [4] did not find an association between race and depression in a study involving primary care patients, results from another cohort study found both race and ethnicity to be related to subsequent development of depressive symptoms. In the Health and Retirement Study [9] both black women and Hispanic women reported significantly more symptoms of depression than white non-Hispanic women (p < 0.001 for both), and Hispanic men had higher levels of depressive symptoms than white non-Hispanic men (p < 0.05).

Female gender is a well-recognized risk factor for depression across all age groups, and several studies have shown that female gender [1, 2, 10] is specifically related to risk of late-life depression. Being of advanced chronological age [3, 11] has also been related to risk of depression in some, but not all, studies. In one cohort of older primary care patients, women had a significantly higher risk of developing depression during the follow-up period than men [12]; a similar association was observed in a cohort of community residents aged 65 and older [13]. Cole and Dendukuri [10] performed a meta-analysis of studies involving middle-aged and older adult community residents, and determined that female gender was a risk factor for depression in this population (Pooled OR = 1.4, 95 % CI = 1.2–1.8), but not old age. Blazer and colleagues [11] found a significant positive association between older age and depressive symptoms in a sample consisting of community-dwelling older adults; however, when potential confounders such as physical disability, cognitive impairment, and gender were included in the analysis, the relationship between chronological age and depressive symptoms was reversed (p < 0.01). A study by Schoevers and colleagues [14] had similar results: being in a higher age stratum corresponded to a greater 3-year risk of incident depression in a bivariate analysis (OR = 1.30, 95 % CI = 1.06–1.60), but this association was not significant in a multivariate analysis. Thus, these findings suggest that higher incidence of depression observed among the oldest-old may be explained by other relevant factors. By contrast, the association of female gender with increased risk of late-life depression has been observed to be a highly consistent finding.

Living alone has also been evaluated as a possible risk factor for late-life depression [15]. In the meta-analysis by Cole et al. [10], older adults who lived alone had a greater odds of developing depression than those who did not, though the association was not significant (Pooled OR = 1.7, 95 % CI = 0.6–4.7). Marital status was not identified as a risk factor in this analysis, as there was no difference in the odds of incident depression in married vs. unmarried individuals. Green and colleagues [12] did not find living or marital status to be related to depression in a prospective study of adults over age 65. Household status at baseline was predictive of depressive symptoms after 2 years among middle-aged men and women in the Health and Retirement Study [9], however; both single men who lived alone (p < 0.001) and single men who lived with others (p < 0.01) had significantly greater levels of depressive symptoms at a follow-up assessment than married men. Single women living with children reported more depressive symptoms at follow-up than married women (p < 0.01), though no difference in the outcome of interest was observed between married women and those who were single and living alone. Thus, a critical factor to note when considering the literature on living alone and late-life depression risk is that living arrangement and marital status are very strongly correlated. Therefore, research that gives attention to creating clear, mutually distinct categories of living and marital status among older persons (e.g., married, widowed and living with others, widowed and living alone, divorced and living with others, divorced and living alone), and then examines whether such status is independently related to late-life depression risk, will be poised to offer more clarity on these questions (Table 3.3).

Numerous studies have delved into the contributions of social factors in late-life depression risk. In an examination of marital bereavement, Turvey et al. [16] analyzed data among 5,449 participants aged ≥ 70 years from the Asset and Health Dynamics Among the Oldest Old Study. Consistent with the strong effects of recent spousal loss reported by Schoevers et al. [1], recently bereaved participants had nearly nine times the odds of developing syndromal depression as married participants (OR = 8.8, 95 % CI = 5.1–14.9, p < 0.0001), and they also had significantly higher risk of depressive symptoms 2 years after the spousal loss. Holley and colleagues [17] examined contributions of both stress levels and spousal loss to late-life depression risk among 1,532 persons in the Changing Lives of Older Couples study (mean age = 69 years). Both stress and spousal loss were independently associated with onset of late-life depression. Furthermore, the observed relation between stress and depression was stronger in the presence of cardiovascular risk factors (CVRFs); however, no interactions between spousal loss and CVRFs were found.