Demographic, Clinical, and Social Factors Associated with an Increased Risk of Death Among Older Adults Aged 75 Years and Older During Heatwaves in Milan, Between Mid-July and Mid-September 2022

Extreme heat is a major weather-related cause of death and is expected to intensify in European cities. We quantified Milan-specific temperature–mortality relationships, defined impact-based heat thresholds around the minimum mortality temperature (MMT) and identified vulnerable subgroups using individual-level risk factors. We conducted a time-stratified case-crossover study including 2230 natural deaths among Milan residents aged ≥75 years occurring between 15 July and 15 September 2022. The MMT (29 °C) was used as the reference temperature [odds ratio (OR) = 1], and mortality risks were evaluated across high-impact (1.20 < OR ≤ 1.50, ≥35 °C) maximum temperature (Tmax) days. Compared with MMT days, mortality was higher on high-impact days (OR 1.44), with somewhat larger estimates among adults aged ≥85 years (OR 1.63) and men (OR 1.50). Disability (OR 1.51) and socioeconomic deprivation (OR 1.89) were also associated with higher vulnerability, with relatively higher estimates observed in women aged ≥85 years and in men with comorbidities or living alone. Overall, the findings suggest that extreme heat may have had a greater impact on the oldest old and on socially or clinically vulnerable groups, highlighting the possible relevance of targeted heat–health interventions and neighborhood-focused prevention strategies.