Purpose: Many studies have reported associations between diet and depression, but few have used formal diagnoses of mood disorder as the outcome measure. We examined if overall diet quality was associated cross-sectionally or longitudinally with DSM-IV mood disorders among an adult cohort.

Methods: Participants from the Australian Childhood Determinants of Adult Health study were followed up during 2004-06 (n = 1974, age 26-36 years), 2009-11 (n = 1480, 31-41 years), and 2014-19 (n = 1191, 36-49 years). Dietary Guidelines Index (DGI) scores were calculated from food frequency questionnaires at each time-point (higher DGI reflects better diet quality). DSM-IV mood disorders (dysthymia or depression) during the periods between, and 12 months prior to each follow-up were determined using the Composite International Diagnostic Interview. Sex-stratified risk and prevalence ratios (PR) and 95% confidence intervals (CI) were estimated using log-binomial regression. Covariates included age, self-perceived social support index score, marital status, parenting status, education, occupation, physical activity, BMI, and usual sleep duration.

Results: A 10-point higher DGI was cross-sectionally associated with lower prevalence of mood disorders at the third follow-up only (females PR = 0.73, 95% CI = 0.56, 0.95; males PR = 0.72, 95% CI = 0.53, 0.97), but was attenuated after covariate adjustment (females PR = 0.92, 95% CI = 0.73, 1.16; males PR = 0.92, 95% CI = 0.69, 1.22). Adjustment for social support in the final model had attenuated the association for both sexes from 18% reduced prevalence to 8%. DGI scores were not longitudinally associated with mood disorder risk.

Conclusions: Crude cross-sectional associations between diet quality and mood disorders at ages 36-49 years were explained by sociodemographic and lifestyle factors, particularly social support.