Alzheimer’s & Dementia: Just a Few Days of Extreme Heat a Year May Be Linked to Dementia Risk

During the follow-up period, 3,773 participants, or 13.2% of the study group, developed dementia. The strongest association was observed among people who were regularly exposed to particularly dangerous heat over several years. When the heat index reached 39.4°C — a measure that accounts for both air temperature and humidity — the risk of dementia in the group with the highest exposure was 23% higher than among those with the lowest exposure.

The researchers also found that the association was particularly pronounced in socially disadvantaged neighborhoods. Among people with high heat exposure, the estimated risk of dementia was 40% higher in the most disadvantaged areas and 11% higher in less vulnerable neighborhoods. Access to air conditioning may also have played a role: the association between extreme heat and dementia was stronger in areas where central air conditioning was less common.

The scientists suggest that extreme heat may affect the brain through impaired blood circulation, inflammation and oxidative stress. Dehydration and sleep disturbances may also exacerbate the effects of overheating. However, the biological mechanisms were not directly investigated in this study.

The authors emphasize that the study identifies an association but does not prove that heat itself causes dementia. Temperature exposure was estimated based on participants’ places of residence rather than their individual circumstances, and dementia was identified through cognitive assessments rather than clinical diagnoses.

The findings highlight the need to account for climate-related risks when developing measures to protect older adults’ health, particularly in neighborhoods with poor housing conditions and limited access to cooling.