Association of Physical Activity with Incidence of Dementia Is Attenuated by Air Pollution

INTRODUCTION: Physical activity (PA) is recognized as one of the key lifestyle behaviors that reduces risk of developing dementia late in life. However, PA also leads to increased respiration, and in areas with high levels of air pollution, PA may increase exposure to pollutants linked with higher risk of developing dementia. Here, we investigate whether air pollution attenuates the association between PA and dementia risk. METHODS: This prospective cohort study included 35,562 adults 60 and older from the UK Biobank. Average acceleration magnitude (ACC(ave)) from wrist-worn accelerometers was used to assess PA levels. Air pollution levels (NO, NO(2), PM(10), PM(2.5), PM(2.5–10), and PM(2.5 absorbance)) were estimated with land use regression methods. Incident all-cause dementia was derived from inpatient hospital records and death registry data. RESULTS: In adjusted models, ACC(ave) was associated with reduced risk of developing dementia (HR [CI]=0.71 [0.60,0.83]), while air pollution variables were not associated with dementia risk. There were significant interactions between ACC(ave) and PM(2.5) (HR(interaction) [CI]=1.33 [1.13,1.57]) and PM(2.5 absorbance) (HR(interaction) [CI]=1.24 [1.07,1.45]) on incident dementia. At the lowest tertiles of pollution, ACC(ave) was associated with reduced risk of incident dementia (HR(PM 2.5) [CI]=0.66 [0.49,0.91], HR(PM 2.5 absorbance) [CI]=0.60 [0.44,0.81]). At the highest tertiles of these pollutants, there was no significant association of ACC(ave) with incident dementia (HR(PM 2.5) [CI]=0.88 [0.68,1.14], HR(PM 2.5 absorbance) [CI]=0.79 [0.60,1.04]). CONCLUSIONS: PA is associated with reduced risk of developing all-cause dementia. However, exposure to even moderate levels of air pollution attenuates the benefits of PA on risk of dementia.