The relationship between air pollution and dementia in mood disorders: The moderating role of sleep patterns-- A prospective study from the UK Biobank.

Purpose: This study aims to quantify dementia risk in mood disorder patients, to examine the association between air pollution and dementia risk, and to assess whether sleep patterns incorporating five specific sleep behaviors modifies this relationship.

Methods: This prospective cohort study enrolled 459,635 individuals from the UK Biobank, 46,256 mood disorder patients at baseline; of those, 1494 developed dementia during follow-up. Air pollution exposure (PM_2.5, PM₁₀, PM_C, NO₂, and NO_X) was estimated using land-use regression models. Sleep patterns were defined according to five sleep domains (sleep chronotype, duration, insomnia, snoring, and daytime sleepiness), with a score ≥ 4 considered healthy. Proportional hazards regression (Cox models) was employed to assess hazard ratios (HRs) for dementia risk. Stratification methodologies were performed to evaluate modification by both individual sleep behaviors and the total sleep pattern score on PM_2.5-dementia associations.

Results: Mood disorders significantly increased dementia risk (HR: 5.69, 95 %CI: 5.36-6.04, P < 0.001). Notably, a significant association with increased dementia risk was observed only for PM_2.5 (HR: 1.67 per 10 μg/m³, 95 % CI: 1.04-2.69, P = 0.034), while PM_C, PM₁₀, NO₂, and NO_X showed no significant associations after comprehensive covariate adjustment. Both five sleep domains and the sleep patterns were found to mitigate the adverse effect of PM_2.5 on dementia risk.

Conclusions: This study reveals that PM_2.5 significantly increases dementia risk in mood disorder patients, while healthy sleep patterns may mitigate this effect. These findings highlight the importance of air pollution control and sleep interventions in dementia prevention to reduce dementia risk in vulnerable populations.