Combined and synergistic effects of heat and fine particulate matter on hospitalization among patients with Alzheimer's disease and related dementias.

BACKGROUND

Patients with Alzheimer's disease and related dementias (ADRD) are vulnerable to environmental stressors such as extreme heat and air pollution, yet their combined health effects remain poorly understood.

METHODS

We assessed the joint impact of extreme heat and fine particulate matter exposure (PM2.5) on the risk of all-cause hospitalization among an ADRD cohort of Medicare beneficiaries aged ≥65 years. Using a time-stratified case-crossover design, we analyzed data from beneficiaries with prior ADRD-related hospitalizations across the contiguous US in 2000-2016. Daily heat index and PM2.5 concentrations were linked to residential ZIP codes, and conditional logistic regression models were applied to estimate same-day associations during the warm season (May-September), including interaction terms to explore potential synergistic effects.

RESULTS

We found a linear association between heat and hospitalization, with an odds ratio (OR) of 1.017 (95% confidence interval [CI] = 1.004, 1.031) on extreme heat days (99th percentile) versus median. The PM2.5-hospitalization relationship was nonlinear, with stronger effects at lower concentrations (10 vs. 5 µg/m3 OR = 1.010; 95% CI = 1.005, 1.015). When accounting for changes in PM2.5, the OR on extreme heat days versus the median was 1.016 (95% CI = 1.001, 1.032).

CONCLUSION

These findings underscore the need to consider both environmental stressors when assessing health risks in ADRD populations.