Allostatic Load, Depressive Symptoms, and Risk of New-Onset Arthritis Among Middle-Aged and Older Adults: A Prospective Study Based on CHARLS

Background: Arthritis is a major cause of pain, functional limitation, and disability among middle-aged and older adults. Although allostatic load (AL) and depressive symptoms have each been linked to adverse health outcomes, prospective evidence on their independent and joint associations with incident arthritis remains limited, particularly in Chinese populations. Methods: This prospective cohort study used data from the China Health and Retirement Longitudinal Study (CHARLS). A total of 8882 participants aged 45 years and older without arthritis at baseline in 2011 were included and followed through 2020. AL was calculated from 11 equally weighted baseline biomarkers (body mass index, systolic and diastolic blood pressure, blood urea nitrogen, total cholesterol, high- and low-density lipoprotein cholesterol, C-reactive protein, glycated hemoglobin, cystatin C, and fasting glucose) using prespecified risk thresholds and categorized as low (0–1), medium (2–3), or high (4–11) burden. Depressive symptoms were measured at baseline using the 10-item Center for Epidemiologic Studies Depression Scale (CESD-10), with a cutoff score of 10. New-onset (incident) arthritis was defined as a newly reported physician diagnosis of “arthritis or rheumatism” during follow-up. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), adjusting for potential confounders. Multiplicative and additive interactions between AL and depressive symptoms were also examined. Results: During follow-up, both higher AL and depressive symptoms were independently associated with an increased risk of new-onset arthritis. In the fully adjusted model, compared with the low-AL group, the HRs for incident arthritis were 1.10 (95% CI: 1.02–1.20) for the medium-AL group and 1.21 (95% CI: 1.04–1.35) for the high-AL group. Participants with depressive symptoms had a significantly higher risk of incident arthritis than those without depressive symptoms (HR = 1.53, 95% CI: 1.41–1.65). No significant multiplicative interaction was observed between AL and depressive symptoms (p for interaction = 0.192). Additive interaction analysis suggested limited evidence of excess joint risk in participants with high AL and depressive symptoms, with an attributable proportion of 0.19 (95% CI: 0.02–0.37). Conclusions: Higher allostatic load and depressive symptoms were independently associated with an elevated risk of new-onset arthritis among middle-aged and older adults. Although no significant multiplicative interaction was identified, their co-occurrence may confer additional risk on an additive scale. These findings highlight the potential relevance of considering both cumulative physiological stress and psychological distress in arthritis risk assessment.