[Association between plasma 25-hydroxyvitamin D level and depressive symptom in older adults aged 65 years and above in 18 longevity areas in China].

The detection rate of depressive symptoms among older adults in 18 longevity areas in China was 6.7%.

• A total of 4,882 participants were included in the analysis.
• 329 out of 4,882 participants screened positive for depressive symptoms (6.7%).
• Mean age of participants was (83.79±11.23) years, with women accounting for 55.1%.
• Depressive symptom was defined as PHQ-9 score ≥10.
• Data were from the 2021 China Healthy Ageing and Biomarkers Cohort Study (cross-sectional).

Higher plasma 25(OH)D level was significantly inversely associated with the risk for depressive symptoms in multivariable logistic regression analysis.

• Participants were stratified into three tertile groups (T1–T3) based on plasma 25(OH)D level.
• Compared with the T1 group, the T3 group had significantly lower risk for depressive symptom (OR=0.678, 95%CI: 0.493–0.928, P=0.016).
• Analysis was adjusted for demographic characteristics, lifestyles, cognitive function, and disease history.
• The association was described as a 'significant inverse association' between plasma 25(OH)D level and depressive symptom.

Higher plasma 25(OH)D level was negatively associated with PHQ-9 score in multiple linear regression analysis.

• T2 group: β=−0.426, 95%CI: −0.701 to −0.151, P=0.002.
• T3 group: β=−0.705, 95%CI: −0.983 to −0.428, P<0.001.
• Both T2 and T3 groups showed statistically significant inverse associations with PHQ-9 score compared to T1.
• The magnitude of the negative association was larger in T3 than T2, suggesting a gradient effect.

Restricted cubic spline models indicated a monotonically decreasing dose-response relationship between plasma 25(OH)D level and risk for depressive symptom.

• The dose-response relationship was monotonically decreasing.
• P for linear trend = 0.010.
• This finding suggests a linear rather than nonlinear relationship between 25(OH)D and depressive symptom risk.
• The restricted cubic spline model was used to flexibly model the continuous relationship between 25(OH)D and depressive symptom risk.

The study used cross-sectional data from the 2021 China Healthy Ageing and Biomarkers Cohort Study conducted in 18 longevity areas in China.

• Information on demographic characteristics, lifestyles, cognitive function, and disease history was collected through face-to-face interviews.
• Fasting venous blood samples were taken to measure plasma 25(OH)D levels.
• Depressive symptom risk was evaluated using the Patient Health Questionnaire-9 (PHQ-9), with score ≥10 indicating a positive result.
• Analytical methods included multivariable logistic regression, multiple linear regression, and restricted cubic spline models.