Association between residential greenness and incident delirium: A prospective cohort study in the UK Biobank

Background: Contemporary environmental health investigations have identified green space as an emerging factor with promising prospects for bolstering human well-being. The incidence of delirium increases significantly with age and is fatal. To date, there is no research elucidating the enduring implications of green spaces on the occurrence of delirium. Therefore, we explored the relationship between residential greenness and the incidence of delirium in a large community sample from the UK Biobank. Methods: Enrollment of participants spanned from 2006 to 2010. Assessment of residential greenness involved the land coverage percentage of green space within a buffer range of 300 m and 1000 m. The relationship between residential greenness and delirium was assessed using the Cox proportional hazards model. Further, we investigated the potential mediating effects of physical activity, particulate matter (PM) with diameters <= 2.5 (PM 2.5 ), and nitrogen oxides (NO x ). Results: Of 232,678 participants, 3722 participants were diagnosed with delirium during a 13.4 -year follow-up period. Compared with participants with green space coverage at a 300 m buffer in the lowest quartile (Q1), those in the highest quartile (Q4) had 15 % (Hazard ratio [HR] = 0.85, 95 % confidence interval [CI]: 0.77, 0.94) lower risk of incident delirium. As for the 1000 m buffer, those in Q4 had a 16 % (HR = 0.84, 95 % CI: 0.76, 0.93) lower risk of incident delirium. The relationship between green space in the 300 m buffer and delirium was mediated partially by physical activity (2.07 %) and PM 2.5 (49.90 %). Comparable findings were noted for the green space percentage within the 1000 m buffer. Conclusions: Our results revealed that long-term exposure to residential greenness was related to a lower risk of delirium. Air pollution and physical activity exerted a significant mediating influence in shaping this association.