Study of 28,512 US adults links days of 39.4 °C or hotter to 23% higher dementia risk
An observational analysis of the Health and Retirement Study found higher dementia incidence among people with more extreme-heat days. The design cannot show that heat causes dementia.
Researchers from the University of Arizona and the University of Southern California analysed Health and Retirement Study data for 2000–2020, covering 28,512 older adults in the United States. They asked whether outdoor heat is associated with incident dementia, according to a paper in Alzheimer s & Dementia. wiley.com
Alzheimer s & Dementiawiley.comOpen source ↗ Each participant was assigned a census-tract-level five-year exposure, adjusted for moves, counting days in two heat categories: "Extreme Caution" (90°F to 102°F, or 32.2°C to 39.3°C) and "Danger+" (≥103°F, or 39.4°C and above). According to the publication's retelling, participants were aged 50 to 89 and were followed for 10.5 years on average. Dementia developed in 3,773 of them (13.2%).
Dementia risk by heat burden
The authors used Fine-Gray subdistribution hazard models and treated death as a competing event. The reference group had a low burden of "Danger+" heat (0.2 days a year or fewer). Compared with it, a moderate burden (0.4 to 1.8 days a year) was associated with a 14% higher risk of dementia onset (95% CI 1.01 to 1.27). A high burden (7.2 days a year or more) was associated with a 23% higher risk (95% CI 1.08 to 1.40). The retelling notes that the relationship was not linear: the intermediate group, with 2 to 7 days a year, showed no significant increase. No association was found for "Extreme Caution" heat.
Socioeconomic factors and limits
The associations were stronger in areas with high socioeconomic disadvantage and low prevalence of central air conditioning. According to the retelling, among the most exposed the excess risk was 36% where air conditioning was scarce and 13% in better-equipped areas. The air-conditioning data date from 2016.
The study is observational and cannot establish that heat causes dementia. Exposure was estimated at neighbourhood level, so conditions inside homes are unknown. Cognitive status came from questionnaires rather than clinical examinations, and dementia subtypes were not distinguished. The authors suggest that prevention efforts consider local heat burden. They also say that populations facing socioeconomic and infrastructural constraints may benefit most from targeted heat-mitigation resources. wiley.com
Alzheimer s & Dementiawiley.comOpen source ↗
