Projected burden of cold spell-attributable Parkinson's disease mortality among older adults in China under climate change and population ageing.

Population ageing may amplify cold-related health risks under climate change, particularly for older adults with Parkinson's disease (PD). We developed a climate-ageing projection framework to estimate the burden of cold spell-attributable PD mortality in China by integrating national mortality data, climate projections, and demographic forecasts. We analyzed 59,384 PD deaths among adults aged 60 years and older in China mainland during 2013-2020 using a time-stratified case-crossover design. Cold spells were associated with an increase in mortality, with effects concentrated within lags 0-4; the cumulative odds ratio was 1.109 (95% CI: 1.036, 1.187), with an attributable fraction (AF) of 9.83% (95% CI: 3.48%, 15.75%). AF point estimates were descriptively higher in southern than in northern China. Across the six administrative regions, AF point estimates ranged from -8.81% in Northwest China to 25.87% in Northeast China, with no statistical evidence of cross-region heterogeneity. Projections showed that cold spell-attributable PD mortality remained substantial across all scenarios in the 2030s, despite climate warming. Thereafter, trajectories diverged. Under SSP1-RCP2.6, projected nationwide attributable deaths were 744 (95% CI: -391, 1,659) in the 2030s, 988 (95% CI: -608, 2,277) in the 2050s, and 867 (95% CI: -589, 2,042) in the 2080s, with East and Southwest China contributing the largest shares and being the only regional estimates whose 95% CIs excluded zero. Under SSP2-RCP4.5, the nationwide burden rose modestly in the 2050s and then declined by the 2080s, whereas under SSP5-RCP8.5 it declined more steeply over time. These scenario-specific patterns occurred alongside substantial differences in projected cold spell occurrence, highlighting that future cold-related PD mortality cannot be inferred from mean warming alone. Under the modeled scenarios, climate warming did not necessarily translate into uniformly lower cold-related PD mortality in an ageing society. This persistence may warrant continued attention to cold-related risks in near-term climate-health adaptation for ageing populations.