Thermoregulatory Stress and the Ageing Mind: Investigating Environmental High Heat Exposure as a Risk Factor for Dementia

Background Extreme heat exposure is a growing public health threat, particularly for older adults. While air pollution is a recognized modifiable risk factor for dementia, the role of sustained high heat exposure remains underexplored. This study investigates the association between cumulative extreme heat exposure and the prevalence of Alzheimer’s disease and related dementias (ADRD) and mild cognitive impairment (MCI) in adults.

Data were drawn from the All of Us Research Program (n = 286 767). High heat exposure was calculated using the CDC’s National Environmental Public Health Tracking Network based on the number of extreme heat days within multi-day events from 2019 to 2023. Exposure was measured using daily maximum temperature and heat index. Diagnoses were identified from electronic health records. Logistic regression models estimated associations between heat exposure and ADRD/MCI, adjusting for demographic, health, behavioral, and socioeconomic variables. Stratified and interaction models assessed differences by age and sex. Findings Every 10 extreme heat days were associated with a 4·0% increase in ADRD/MCI odds using maximum temperature (OR=1·040, 95% CI: 1·026–1·051) and a 6·0% increase using heat index (OR=1·058, 95% CI: 1·044–1·071). Using age-stratified analysis the effect was stronger among adults aged ≥70, with odds increasing by 7·8% versus 3·9% among those <70 using heat index. A significant interaction by age was observed (p<0·001). Odds ratios were slightly higher in females, but sex did not significantly modify the association. Area deprivation accounted for 8·6%–9·6% of the association, while education and social isolation were not significant mediators. Interpretation Cumulative high heat exposure is associated with increased odds of ADRD/MCI, especially among adults aged 70 and older. These findings underscore the need for climate adaptation strategies targeting older and socioeconomically disadvantaged populations. Funding This research was supported by the All of Us Research Program, and funded by the National Institutes of Health. Evidence before this study We searched PubMed and Google Scholar for studies published between January 2005 and April 2025 using combinations of the terms “extreme heat,” “heat exposure,” “heat waves,” “dementia,” “Alzheimer’s disease,” “cognitive impairment,” and “older adults.” While many studies have shown that older adults face increased mortality and morbidity during extreme heat events, few have explored cognitive outcomes. Research specifically linking heat exposure to Alzheimer’s disease and related dementias (ADRD) is scarce. Most existing studies focus on short-term heat events and general health or mortality outcomes, rather than dementia. Although some evidence suggests temporary cognitive effects from heat, robust studies on diagnosed ADRD are lacking. Only one study has assessed the impact of cumulative extreme heat on cognitive function, and it did not examine clinical diagnoses or adjust for comorbid conditions. Added value of this study To our knowledge, this is the first national-level study in the United States to examine the association between cumulative high heat exposure and diagnosed ADRD or mild cognitive impairment (MCI) using detailed individual-level electronic health records. Our study used five years of environmental exposure data (2019–2023) and two distinct metrics—maximum temperature and maximum heat index—linked to a large, diverse cohort from the All of Us Research Program. We adjusted for demographic, clinical, behavioral, and social factors and explored interactions by age and sex. We also assessed mediation of the relationship by area deprivation, education, and social isolation. Our findings reveal that cumulative heat exposure is associated with increased odds of ADRD/MCI and that risk is more pronounced among individuals aged 70 and older. Implications of all the available evidence Cumulative high heat exposure may contribute to neurocognitive risk in later life, particularly among older adults. Our findings suggest that neighborhood-level socioeconomic disadvantage partly explains this association, underscoring the influence of structural and environmental conditions on dementia risk. This research supports the integration of heat-related vulnerability into dementia prevention frameworks and climate adaptation strategies. As climate change intensifies, understanding how environmental stressors such as heat affect cognitive ageing is essential for public health planning and policy. Targeted interventions and protective measures for older adults may help mitigate these long-term cognitive impacts. Competing Interest Statement The authors have declared no competing interest. Funding Statement This study did not receive any funding Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The institutional review board of SUNY Downstate Health Sciences University waived ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability All data produced in the present study are available online through the All of Us Researcher Workbench