Association of Dual Sensory Impairment-Depression Comorbidity Patterns with Fall Risk Among Middle-Aged and Older Adults: A Nationwide Cohort Study

Technical Summary: Association of Dual Sensory Impairment-Depression Comorbidity Patterns with Fall Risk Among Middle-Aged and Older Adults

Problem Statement
Falls represent a leading cause of injury-related mortality globally, with a particularly high burden among older adults in China. While Dual Sensory Impairment (DSI)—the co-occurrence of visual and hearing impairment—and depression are both established, independent risk factors for falls, their synergistic effects when comorbid remain underexplored. Previous research has largely examined these conditions in isolation, failing to quantify the specific risk patterns associated with their coexistence or to elucidate the bidirectional mediating pathways between sensory decline, mental health, and fall risk. This study addresses the gap in understanding how DSI-depression comorbidity patterns influence fall risk trajectories in middle-aged and older Chinese adults.

Methodology
This research utilized a prospective cohort design based on data from the China Health and Retirement Longitudinal Study (CHARLS).

• Participants: The study enrolled 9,833 participants aged 45 years and older. After excluding individuals with missing data on sensory function, depression, or fall history, and those lost to follow-up, the final analytical sample consisted of 9,833 individuals.
• Exposure Definition: Participants were categorized into four distinct groups based on the cross-classification of DSI and depressive symptoms:
  1. Dual low-risk: No DSI and no depression.
  2. DSI only: DSI without depression.
  3. Depression only: Depression without DSI.
  4. DSI-depression comorbidity: Both DSI and depression.
  • DSI Assessment: Defined as the co-occurrence of self-reported visual impairment (difficulty recognizing a friend across the street or reading newspaper print) and hearing impairment.
  • Depression Assessment: Measured using the 10-item Center for Epidemiologic Studies Depression Scale (CESD-10), with a score ≥10 indicating depressive symptoms.
• Outcome: The primary outcome was the occurrence of self-reported falls during a 9-year follow-up period (2013–2020).
• Statistical Analysis:
  • Survival Analysis: Kaplan-Meier curves with log-rank tests were used to compare cumulative fall incidence across groups.
  • Regression Modeling: Cox proportional hazards models were employed to estimate Hazard Ratios (HR) for fall risk. Three models were constructed: an unadjusted model, a model adjusted for demographics (age, sex, marital status, education, residence, BMI), and a fully adjusted model further controlling for lifestyle factors and comorbidities (smoking, alcohol, hypertension, diabetes, dyslipidemia, heart disease, stroke, arthritis).
  • Mediation Analysis: A counterfactual framework using Bootstrap methods (5,000 resamples) was conducted to assess the bidirectional mediating effects of DSI and depression on fall risk.
  • Subgroup Analysis: Stratified analyses were performed to test for effect modification by age, sex, residence, marital status, education, and specific comorbidities.

Key Results

• Incidence: By the end of the follow-up, 3,870 participants (39.36%) experienced at least one fall.
• Cumulative Incidence: Significant differences were observed across the four comorbidity patterns (P < 0.001). The cumulative incidence of falls was highest in the DSI-depression comorbidity group (51.15%), followed by the depression-only group (44.22%), the DSI-only group (38.35%), and the dual low-risk group (32.59%).
• Risk Quantification: In the fully adjusted Cox regression model, compared to the dual low-risk group:
  • The DSI-depression comorbidity group showed a 45% increased risk of falls (HR = 1.45, 95% CI: 1.33–1.58).
  • The depression-only group showed a 27% increased risk (HR = 1.27, 95% CI: 1.15–1.40).
  • The DSI-only group showed a 12% increased risk (HR = 1.12, 95% CI: 1.03–1.22).
• Mediation Effects: The analysis revealed bidirectional partial mediation:
  • Depression partially mediated the association between DSI and fall risk, accounting for 18.33% of the total effect.
  • Conversely, DSI partially mediated the association between depression and fall risk, accounting for 7.26% of the total effect.
  • The authors note that direct effects remained the primary pathway for both associations.
• Robustness: Subgroup analyses confirmed that the increased fall risk associated with DSI-depression comorbidity was consistent across all demographic and clinical strata, with no significant interaction effects detected.

Significance and Claims
The paper claims to be the first nationwide prospective cohort study to systematically investigate the association between DSI-depression comorbidity patterns and fall risk, specifically quantifying the excess risk of the comorbid state compared to single conditions.

• Synergistic Risk: The study demonstrates that the combination of DSI and depression confers a significantly higher fall risk than either condition alone, suggesting a synergistic rather than merely additive effect.
• Bidirectional Pathways: By identifying that DSI and depression mutually mediate each other's association with fall risk, the study provides a more comprehensive pathway map for understanding the tripartite relationship between sensory decline, mental health, and physical safety.
• Public Health Implications: The findings suggest that fall prevention strategies should shift earlier to the middle-aged stage (45+) and target DSI-depression comorbidity as a universal high-risk indicator, rather than limiting interventions to specific subgroups. The authors advocate for comprehensive screening and integrated interventions at primary healthcare levels.
• Limitations: The authors modestly acknowledge that as an observational study, causal relationships cannot be definitively established. They note limitations regarding self-reported data (potential recall and information bias), the inability to distinguish severity levels of sensory impairment, and the exploratory nature of the mediation analysis which relies on cross-sectional exposure-mediator associations rather than strict temporal causal inference.

In conclusion, the study provides epidemiological evidence that DSI-depression comorbidity is a critical, modifiable risk factor for falls, warranting integrated clinical attention to prevent injury-related mortality in aging populations.