Association of the sarcopenia index with incident depressive symptoms and adverse depressive symptom trajectories

The sarcopenia index (SI) is an accessible marker associated with muscle health, with cross-sectional link to depression has been reported. However, longitudinal evidence between baseline SI and future depressive symptoms is limited, without investigations on heterogeneous symptom trajectories. We intended to figure out the correlation of baseline SI and both the incidence of depressive symptoms and membership in distinct depressive symptom trajectories.

Utilizing data from the Health and Retirement Study (2016-2022), our cohort included 6,286 participants free of depressive symptoms at baseline for the incident analysis and 5,699 for the trajectory analysis. Distinct symptom patterns were identified using group-based trajectory modeling (GBTM) across four waves. Associations were determined using Cox proportional hazards regression for incident depressive symptoms and multinomial logistic regression for trajectory membership.

Over the 6-year follow-up, 1,311 participants developed depressive symptoms (incidence rate: 47.73 per 1,000 person-years). Each standard deviation (SD) increase in baseline SI was connected to decreased likelihood of incident depressive symptoms (Hazard Ratio [HR] = 0.91; 95% Confidence Interval [CI]: 0.85-0.98; p = 0.008). When analyzed by quartiles, the highest quartile (Q4) was linked to diminished likelihood of incident depressive symptoms compared to the lowest quartile (Q1; HR = 0.80; 95% CI: 0.66-0.96; p = 0.018). Moreover, this association demonstrated a linear dose-response relationship among all subgroups and remained robust across sensitivity analyses. Furthermore, four distinct trajectories were identified by GBTM, including "Non-depressed" (28.09%), "Low-stable" (40.61%), "Moderate-progressive" (26.04%), and "High-progressive" (5.26%). A higher baseline SI was associated with significantly lower odds of belonging to the "High-progressive" trajectory (Per SD increase: Odds Ratio [OR] = 0.88; 95% CI: 0.80-0.97; p = 0.008). But the association was specific to adverse patterns, showing no association with the "Low-stable" trajectory (p = 0.973).

Consistent association was observed between a higher baseline sarcopenia index and both a lower likelihood of incident depressive symptoms and a lower risk of membership in adverse symptom trajectories in older adults. These findings highlighted the utility of SI on identifying individuals at elevated risk for unfavorable long-term depressive symptom progression among older population.