Frailty Transforms Care Continuity‐Mortality Relationships Across Age Groups: Evidence From Taiwan and South Korea

BACKGROUND: Healthcare fragmentation typically predicts poor outcomes, yet its relationship with frailty across different age groups remains unexplored. We examined how frailty modifies the association between care patterns and mortality in middle-aged and older adults from two rapidly ageing Asian societies. METHODS: We analysed national insurance data from Taiwan (n = 370 997) and South Korea (n = 392 466) for adults aged ≥ 45 years, categorised as middle-aged (45-64) and older (≥ 65) groups. Frailty was assessed using a validated multimorbidity frailty index. We measured healthcare utilisation, care fragmentation (Usual Provider of Care UPC, Bice-Boxerman Continuity of Care Index COCI, Sequential Continuity Index SECON) and 3-year mortality. Cox proportional hazards models were used to estimate adjusted hazard ratios(aHRs) between healthcare utilisation as well as care fragmentation and risk of mortailty. RESULTS: Frailty prevalence increased with age in both countries (Taiwan: 19.2% middle-aged, 53.8% older adults; South Korea: 24.7%, 63.0%). Healthcare utilisation increased sharply with frailty severity. Among middle-aged adults, severely frail individuals had substantially more outpatient visits than fit individuals (Taiwan: 56.5 ± 31.0 versus 13.2 ± 10.4; South Korea: 67.1 ± 55.1 versus 13.3 ± 11.7). Hospitalisation rates rose dramatically from 6.1% (fit) to 70.9% (severely frail) in middle-aged and 6.8% (fit) to 68.6% (severely frail) in older Taiwanese, with similar increases in South Korea (10.8% to 67.5% in middle-aged and 10.2% to 62.5% in older groups, respectively). Care continuity declined with increasing frailty. In Taiwan, UPC decreased from 0.81 ± 0.18 in fit to 0.69 ± 0.17 in the severely frail among middle-aged adults, with similar declines in COCI and SECON. Declines were less pronounced in South Korea, where severely frail older adults maintained higher continuity (UPC 0.78 ± 0.16) than their Taiwanese counterparts (0.68 ± 0.17). During 3-year follow-up, higher care fragmentation was associated with increased mortality among fit middle-aged adults (aHR 1.69, 95% CI 1.14-2.50) but showed inverse associations among moderately frail individuals (aHR 0.67, 95% CI 0.31-1.42), consistently across both countries and age groups. CONCLUSION: Frailty, not age, fundamentally transforms how care patterns relate to mortality. The fragmentation-mortality paradox across age groups indicates that frailty-specific coordination approaches are needed throughout the adult life course. Healthcare systems must implement standardised frailty service frameworks, develop accessible specialised geriatric services and design integrated care models that optimise the quality, efficiency and sustainability of healthcare systems in rapidly ageing societies.