Prospective study on the association between diet quality and depression in mid-aged women over 9 years

To examine the longitudinal association between diet quality and depression using prospective data from the Australian Longitudinal Study on Women's Health.

Women born in 1946-1951 (n = 7877) were followed over 9 years starting from 2001. Dietary intake was assessed using the Dietary Questionnaire for Epidemiological Studies (version 2) in 2001 and a shortened form in 2007 and 2010. Diet quality was summarised using the Australian Recommended Food Score. Depression was measured using the 10-item Centre for Epidemiologic Depression Scale and self-reported physician diagnosis. Pooled logistic regression models including time-varying covariates were used to examine associations between diet quality tertiles and depression. Women were also categorised based on changes in diet quality during 2001-2007. Analyses were adjusted for potential confounders.

The highest tertile of diet quality was associated marginally with lower odds of depression (OR 0.94; 95 % CI 0.83, 1.00; P = 0.049) although no significant linear trend was observed across tertiles (OR 1.00; 95 % CI 0.94, 1.10; P = 0.48). Women who maintained a moderate or high score over 6 years had a 6-14 % reduced odds of depression compared with women who maintained a low score (moderate vs low score-OR 0.94; 95 % CI 0.80, 0.99; P = 0.045; high vs low score-OR 0.86; 95 % CI 0.77, 0.96; P = 0.01). Similar results were observed in analyses excluding women with prior history of depression.

Long-term maintenance of good diet quality may be associated with reduced odds of depression. Randomised controlled trials are needed to eliminate the possibility of residual confounding.