Outdoor extreme heat-related dementia risk and the role of socioeconomic disparities: evidence from 20 years of data on US older adults.

INTRODUCTION

Extreme heat is increasingly recognized as a significant threat to brain health. However, human evidence from large, longitudinal studies remains limited. We examine whether outdoor heat exposure is associated with incident dementia and whether socioeconomic factors moderate this risk.

METHODS

Leveraging data from the 2000 to 2020 Health and Retirement Study (N = 28,512), we assigned census-tract-level 5-year exposure to the number of "Extreme Caution" (90°F to 102°F [32.2°C to 39.3°C]) and "Danger+" (≥103°F [39.4°C]) heat days, adjusting for moves. Fine-Gray subdistribution hazard models estimated dementia risk, treating death as a competing event.

RESULTS

Compared with individuals with a low burden of "Danger+" heat (≤0.2 days/year), those with a moderate burden (0.4 to 1.8 days/year) and a high burden (≥7.2 days/year) had 14% (95% confidence interval [CI] = 1.01 to 1.27) and 23% (95% CI = 1.08 to 1.40) higher risks of dementia onset, respectively. Stronger associations were found among individuals in areas with high socioeconomic disadvantage and low central air conditioning prevalence. No associations were found for "Extreme Caution" heat.

DISCUSSION: Outdoor extreme heat may represent an important environmental risk factor for dementia, particularly among older adults living in areas characterized by structural barriers to mitigating exposure. Our findings suggest that dementia prevention efforts should consider local heat burden and prioritize strategies to reduce cumulative thermal stress. Greater attention should be directed toward identifying populations facing socioeconomic and infrastructural constraints that may benefit most from targeted heat-mitigation resources and support.