Sunlight Exposure, Depressive Symptoms, and Cognitive Function Among Older Adults in Nursing Homes: A Cross-Sectional Mediation Analysis

Cognitive impairment and depressive symptoms are common among nursing home residents. The indirect association between sunlight exposure and cognitive function through depressive symptoms in this setting remains unclear.

This cross-sectional study included 244 older adults from six nursing homes in Chengdu, China. Sunlight exposure, depressive symptoms, and cognitive function were assessed using the Chinese version of the Sunlight Exposure Questionnaire, the 15-item Geriatric Depression Scale (GDS-15), and the Montreal Cognitive Assessment-Basic, respectively. GDS-15 total scores were used for correlations and regressions; three item parcels represented depressive symptoms in the structural model. Correlation analysis, multivariable linear regression, and structural equation modeling with 5000 bootstrap resamples were performed.

The mean age was 82.42 years, and 132 participants (54.1%) were women. Mean sunlight exposure, depressive symptom, and cognitive function scores were 1.93 (SD 0.43), 4.07 (SD 3.22), and 20.27 (SD 2.02), respectively. Sunlight exposure correlated negatively with depressive symptoms (r = -0.297) and positively with cognitive function (r = 0.221); depressive symptoms correlated negatively with cognitive function (r = -0.195; all P < 0.01). In the structural equation model, sunlight exposure was associated with fewer depressive symptoms (standardized β = -0.323), and depressive symptoms were associated with lower cognitive function (β = -0.155). The standardized indirect association through depressive symptoms was 0.050 (bias-corrected 95% bootstrap CI: 0.004-0.114; bootstrap P = 0.042), representing 24.0% of the total modeled association. The direct association was 0.158 (bias-corrected 95% bootstrap CI: 0.002-0.308). Model fit was acceptable (χ²/df = 2.091, CFI = 0.957, RMSEA = 0.067).

Greater sunlight exposure was modestly associated with fewer depressive symptoms and better cognitive function. Depressive symptoms represented a partial statistical indirect pathway; the cross-sectional design cannot establish temporal order or causality. Longitudinal studies are needed to clarify these relationships.