Higher Cardiorespiratory Fitness Cuts Depression Risk in US and UK Elders But Not in China

Depression affects over 279 million people globally and is especially burdensome in aging populations. Cardiorespiratory fitness (CRF)—the body's capacity to take up and utilize oxygen during exercise—is a well-established modifiable risk factor for cardiovascular disease and mortality. Whether CRF also predects incident depression in older adults, and whether that relationship holds across different national and cultural contexts, was previously unclear.

This prospective cohort study pooled data from three harmonized national aging surveys: the Health and Retirement Study (HRS, United States; n=4,195), the English Longitudinal Study of Ageing (ELSA, England; n=5,421), and the China Health and Retirement Longitudinal Study (CHARLS, China; n=4,064). Participants were adults aged 50 and older who were free of depressive symptoms at baseline. Estimated CRF (eCRF) was calculated using validated sex-specific algorithms incorporating age, BMI, waist circumference, resting heart rate, physical activity, and smoking status, and expressed in metabolic equivalents (METs). Participants were categorized into low (quintile 1), moderate (quintiles 2–3), and high (quintiles 4–5) eCRF groups. Depressive symptoms were assessed longitudinally using the CES-D scale (8-item in HRS/ELSA; 10-item in CHARLS), with clinically meaningful thresholds applied. Cox proportional hazards models adjusted for demographic, lifestyle, and clinical covariates were used, supplemented by restricted cubic splines to assess dose-response relationships.

After median follow-ups of 9.78, 12.11, and 5.73 years in HRS, ELSA, and CHARLS respectively, incident depressive symptom rates were 22.79%, 22.15%, and 40.58%. Each 1-SD increase in eCRF was associated with a 9% lower depression risk in HRS (HR=0.91; 95% CI 0.87–0.96) and 8% lower in ELSA (HR=0.92; 95% CI 0.87–0.97). In sharp contrast, the same increase was associated with a 6% higher risk in CHARLS (HR=1.06; 95% CI 1.01–1.16). Comparing high vs. low eCRF groups, the protective effect was pronounced in HRS (HR=0.69) and ELSA (HR=0.62), while CHARLS showed an elevated risk (HR=1.27; 95% CI 1.01–1.61). Subgroup analyses identified effect modification by smoking status in HRS, by gender and diabetes status in ELSA, and by hypertension in CHARLS.

The unexpected finding in China may reflect several cultural and contextual factors. Chinese older adults with higher eCRF may be more physically active in occupational or subsistence contexts (e.g., farm labor) rather than leisure exercise, which differs qualitatively in its psychosocial benefits. Social isolation, loss of traditional roles, economic pressures on rural elderly, and distinct depression manifestation patterns in Chinese culture may all overwhelm any fitness-related benefit. Additionally, the CHARLS cohort had a substantially higher depression incidence (40.58% vs. ~22% in Western cohorts), suggesting a different baseline burden and risk architecture.

Caveats include the non-exercise-based estimation of CRF (though eCRF algorithms are validated), use of different CES-D versions across cohorts, potential residual confounding, and the shorter follow-up in CHARLS. Despite harmonization efforts, unmeasured cultural and socioeconomic differences between cohorts may contribute to the divergent findings. Findings should be interpreted as hypothesis-generating for China-specific mechanisms rather than definitive causal evidence.