Associations of dietary diversity trajectories with depressive symptoms among Chinese older adults: a 10-year longitudinal study

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Background Depression is one of the most prevalent mental health conditions among older adults in China, profoundly impairing quality of life and impeding healthy aging. Dietary diversity, as a comprehensive indicator of overall diet quality, has been associated with various chronic diseases and mental health outcomes. However, the association between longitudinal trajectories of the Dietary Diversity Score (DDS) and depressive symptoms among older adults remains poorly understood. Methods Using four waves of longitudinal data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) spanning 2008 to 2018, a total of 1,538 participants aged ≥65 years were included. Latent Class Growth Analysis (LCGA) was applied to identify distinct long-term DDS trajectories, with CESD-10 depressive scores assessed in 2018 serving as the primary outcome. Three multivariable linear regression models examined the associations between DDS trajectories and depressive scores with stepwise covariate adjustment. Binary logistic regression sensitivity analyses, subgroup analyses, and Restricted Cubic Spline (RCS) analyses were conducted to examine the association between the number of teeth and depressive scores. Results LCGA identified three DDS trajectories: stable (Class 1, n = 946), high-decreasing (Class 2, n = 205), and low-increasing (Class 3, n = 387). In the fully adjusted model, compared with Class 1, Class 2 had lower depressive scores ( B = −0.902, 95% CI: −1.800 to −0.005), whereas Class 3 had higher depressive scores ( B = 0.901, 95% CI: 0.200–1.602). Sensitivity analyses confirmed that Class 3 was associated with a higher risk of depressive symptoms (OR = 1.405, 95% CI: 1.064–1.857). RCS analyses revealed a nonlinear association between the number of teeth and depressive scores ( p < 0.001), with predicted depressive scores showing a pronounced and sustained decline when the number of teeth exceeded 20. Conclusion Long-term maintenance of higher dietary diversity was associated with lower depressive scores among Chinese older adults. A nonlinear dose–response relationship was observed between number of teeth and depressive symptoms. These findings suggest that maintaining greater dietary diversity in early aging, together with good oral health, higher health literacy, and better quality of life, may be associated with better mental health in older adults.