Associations of ambient air pollution exposure and sleep pattern with brain structures: A prospective study in the UK Biobank

Background: Previous studies have shown associations between exposure to air pollution (AP) and total gray matter volume (GMV) and total white matter volume (WMV). However, no study has explored the impact of sleep conditions (sleep behaviors and sleep patterns) on the associations between AP and brain structures. Methods: This study included over 21,000 participants from the UK Biobank. Neuroimaging data were processed to obtain measures of global brain volume, GMV, and WMV, as well as white matter hyperintensity volume (WMHV). Land use regression model was utilized to estimate the concentrations of AP, including PM2.5, PM2.5-10, PM10, NO2, NOx, and PM2.5absorbance. Sleep behaviors included chronotype, duration, insomnia, snoring, and daytime sleepiness. These behaviors were utilized to calculate a healthy sleep score and then applied to categorize sleep patterns as healthy, intermediate, or poor. The doubly robust method was used to estimate the associations between AP, sleep conditions, and brain structures. Results: This study found that PM2.5, NO2, NOX, and PM2.5absorbance were significantly inversely associated with global brain, GMV and WMV. PM2.5, NO2, and NOX showed significant positive associations with WMHV, with beta (95 %CI) coefficients of 0.016 (0.005, 0.027), 0.016 (0.005, 0.026), and 0.018 (0.006, 0.031), respectively. Sleep patterns were positively associated with global brain and WMV. Sleep duration modified the associations between the three kinds of AP (PM2.5, PM10, PM2.5absorbance) and WMHV (P-interaction<0.05). The associations of PM2.5 and NO2 with the global brain and WMV decreased as sleep patterns improved. Conclusions: AP was associated with adverse effects on brain outcomes, while healthy sleep conditions were linked to favorable brain outcomes. Low-risk sleep behaviors and healthy sleep pattern may mitigate the detrimental associations of AP with brain structures.