Heat-related mortality burden of type 1 diabetes, type 2 diabetes, and diabetes complications in mainland China amid global warming: a nationwide, case-crossover study

Background

Rising global temperatures and diabetes pose growing health risks worldwide. Individuals with diabetes are particularly vulnerable to heat, mainly because of impaired thermoregulation. However, the specific heat-related mortality risks associated with diabetes subtypes and complications remain poorly quantified.

Methods

We conducted a nationwide, individual-level, time-stratified case-crossover study encompassing 289 902 diabetes-related deaths across mainland China from 2013 to 2019. Death records for 2013–19 were sourced from the China Cause of Death Reporting System, a nationwide surveillance system. We used conditional logistic regression incorporating a distributed lag non-linear model to estimate temperature–mortality associations at the national level for overall diabetes, primary diabetes subtypes (type 1 and type 2), and specific complications (diabetic coma, diabetic ketoacidosis, diabetic nephropathy, and diabetes with peripheral vascular disease [PVD]). We examined how the associations varied across the temperate continental, temperate monsoon, and subtropical monsoon zones. The future heat-attributable diabetes mortality burden up to 2099 was projected under three shared socioeconomic pathways (SSP126 [low emissions], SSP245 [moderate emissions], and SSP585 [high emissions]). Additionally, we modelled several adaptation scenarios by assuming 10%, 30%, and 50% reductions in the exposure–response coefficients.

Findings

Exposure to extreme high temperatures (97·5th percentile [31·0°C]) compared with the minimum mortality temperature was associated with an increase in overall diabetes mortality (odds ratio [OR] 1·25, 95% CI 1·22–1·29) over a 0–6 day lag period, with the magnitude of risk higher in cooler regions. Heat-related mortality outcomes for diabetes subtypes and complications varied geographically. In warmer zones, individuals with type 2 diabetes were at higher risk of mortality than those with type 1 diabetes (eg, OR 1·21 [95% CI 1·16–1·26] vs 1·14 [1·04–1·26] in the subtropical monsoon zone [warmest region]), whereas the opposite held in cooler zones (1·31 [1·09–1·58] vs 1·65 [1·17–2·33] in the temperate continental zone [coldest region]). By climate zone, the most heat-sensitive complications were diabetic ketoacidosis and nephropathy, in the subtropical zone; PVD and nephropathy, in the temperate monsoon zone; and diabetic coma and PVD, in the temperate continental zone. We projected that by the 2090s, under a high emission scenario (SSP585), the heat-attributable fraction of diabetes deaths would reach 11·16% (empirical 95% CI 6·11–18·01). In the temperate continental zone, we projected a burden of 29·02% (7·53 to 44·58) of diabetes coma deaths attributable to heat, followed by PVD (28·65% [–22·60 to 46·95]) and nephropathy (17·40% [–4.41 to 31·27]). Population ageing and growth were projected to increase the burden of overall heat-attributable diabetes mortality by approximately 1 percentage point, whereas implementation of a 50% adaptation scenario was projected to reduce the burden by about 5 percentage points.

Interpretation

Our study showed regional heterogeneity in the risk of heat-related mortality associated with diabetes subtypes and complications, calling for highly tailored, climate-aware public health responses to safeguard clinically vulnerable diabetic populations in a warming world.