Demographic transitions and the slow realignment of medical specialization: a 25-year analysis of physician distribution across OECD and partner economies (2000–2024)

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Background Demographic transformation has redefined the global demand for medical specialties, yet evidence on how physician distributions adapt remains limited. This study examined temporal and demographic determinants of specialty composition across Organisation for Economic Co-operation and Development (OECD) and partner countries from 2000 to 2024. Methods We harmonized OECD Health Statistics (2024), United Nations World Population Prospects (2024), and World Bank health indicators to construct a longitudinal dataset for 48 economies. Specialty densities (pediatrics, geriatrics, psychiatry, internal medicine, surgery, obstetrics–gynecology, and primary care) were standardized per 100 000 population. Demographic covariates included the fertility rate, the population aged ≥ 65 years, and the dependency ratio. Fixed-effects and distributed-lag panel regressions assessed the elasticity of specialty supply to demographic change, with robust standard errors clustered by country. Results Global physician density increased from 253 to 338 per 100 000 between 2000 and 2024, but compositional adaptation lagged demographic transition. Pediatrician density declined by 32%, while geriatrics and psychiatry grew by 145% and 71%, respectively. Each 1-unit decrease in total fertility rate was associated with a 0.43% reduction in pediatrician density ( p < 0.001), whereas each 1-point rise in the share of older adults corresponded to a 0.58% increase in geriatric density ( p = 0.002). Distributed-lag analysis indicated 4–6-year delays in fertility-driven adjustments and up to 10 years for aging-related expansion. High-income OECD members displayed greater geriatric elasticity than middle-income partners (0.74 vs 0.38). The pediatric-to-geriatric ratio declined from 7.9 to 2.4 globally. Conclusions Despite overall physician growth, structural inertia constrains the alignment of medical specialization with population aging. Demographic sensitivity varies across income groups and institutional capacities, revealing a persistent mismatch between workforce composition and societal needs. Integrating demographic forecasting into medical education and planning is essential to prevent widening gaps in geriatric, psychiatric, and primary-care services.