Effect of HEPA filtration air purifiers on cognitive function from a secondary outcome analysis of a pragmatic randomized crossover trial

Exposure to particulate matter is associated with adverse health outcomes such as cardiovascular and neurological diseases. However, there are few intervention studies that have examined short-term changes in air particulate exposure and cognitive outcomes. Data from 119 participants were analyzed in the Home Air Filtration for Traffic-Related Air Pollution (HAFTRAP) study, a pragmatic randomized crossover trial. Participants were randomized to receive a high efficiency particulate arrestance (HEPA) air purifier for one month, a washout period of one month, then a sham unit for one month or vice versa. Time to complete Trail Making Test – Parts A and B were recorded at the beginning and end of each intervention period. Although there was no significant overall difference in completion times of the Trail Making Tests between HEPA and sham filtration, age was a significant moderator (test for interaction p = 0.02). Participants 40 years or older with HEPA filtration completed Part B 12% significantly faster than participants who had sham filtration in the preceding month (54.0 versus 61.4 s, ratio of means = 0.88, p = 0.02). No significant reduction in completion time was observed for participants < 40 years old. Among older healthy adults, there was an improvement in cognition following one month of in-home HEPA filtration. Further research is needed on the short-term effects of air pollution among individuals with some level of cognitive impairment.