Measures of life course household income and depressive symptoms in the Alameda County Study, 1965-1999

Lower socioeconomic position is associated with increased risk for depression. However, few studies have compared the strength of associations between recent, long-term, or trajectories of income over time and depressive symptoms. Using logistic regression models, three household income measures were studied in relation to experiencing five or more depressive symptoms in 1999: recent income (1999), average income (1965-1999), and income trajectory patterns (1965-1999). Alameda County Study data from the 2102 (n_men=905, n_women=1195) of the 2123 respondents to the 1999 questionnaire with age, race/ethnicity, marital status, and income data were used in these analyses. Income trajectories were categorized as persistently low-decreasing, persistently low-increasing, moderately low, moderately low-increasing, increasing, and high-parabolic. Controlling for age, race/ethnicity, marital status and gender, membership in the lowest (Odds Ratio (OR) =3.2, 95% Confidence Interval (CI) = 1.9-5.4) and second (OR =1.8, 95% CI=1.0-3.0) quartiles of income in 1999 compared to the highest quartile was associated with greater odds of multiple depressive symptoms. Adults with average income in the lowest (OR =2.6, 95% CI=1.6-4.3) and second (OR=2.0, 95% CI=1.2-3.4) compared to highest quartile and the persistently low-increasing (OR=3.6, 95% CI=1.7-7.8) and moderately low (OR=2.3, 95% CI=1.2-4.5) compared to high-parabolic trajectory had increased odds of depressive symptoms. While associations were present between each income measure and depressive symptoms, effect size was largest for trajectories, followed by current and average income measures respectively. Studies investigating income effects on mental health should be selective and purposeful when determining the income measure for analysis.