People living near high-traffic roads are exposed to increased levels of particulate matter (PM), brake, and tire wear particles. PM2.5 and ultrafine particles (UFP) can enter the homes even without mechanical ventilation or well-sealed building envelopes. Exposure to PM is associated with cardiovascular disease through increased blood pressure (BP). As per the epidemiologic evidence, there is a rise in the risk of stroke, death, and myocardial infarction due to increased BP. Increases in both systolic BP and diastolic BP are substantially linked to increased risk of vascular disease and overall mortality. This study aimed to determine the effectiveness of in-home air purifiers in decreasing BP among individuals residing near highways.
A randomized crossover trial was conducted in eastern Massachusetts, enrolling 207 people from 172 residences during colder months when traffic-related PM levels are higher. Eligible participants were individuals aged 30 or older, cognitively capable of completing questionnaires, and who spoke fluent Spanish or English. All residences were located within 200 m of high-traffic highways. Individuals were randomized to one month of high-efficiency particulate arrestance (HEPA) sham or air filtration, followed by one month of washout before crossing over. Blinding was maintained by using identical units with sham devices containing inactive filters. Air purifiers were installed in both the living room and the bedroom. Electricity use loggers indicated ~99% of operation time. BP was monitored at four visits, and questionnaires were used to assess indoor time, stress, health status, and environmental exposures.
The main results were variation in systolic BP (SBP) with the model adjusted for age, stress, sex, indoor time, outdoor temperature, and baseline BP. Analyses involved an SBP-by-intervention interaction term (<120 mm Hg versus ≥120 mm Hg) because of earlier evidence of effect modification. Sensitivity analyses investigated alternative SBP cut-offs. Linear mixed models were utilized to evaluate PM reduction efficacy. Statistical significance was determined at a p-value of <0.05.
This study found that in-home HEPA filtration considerably decreased indoor PM levels and UFP number counts (PNC) as compared to sham filtration. The largest reduction occurred during midday and evening cooking hours, with the lowest pollutant levels observed at night, close to the time of BP measurement. The final analysis included 154 individuals with a mean age of 41.1 years, a mean baseline BP of 118.8/76.5 mm Hg, and a 59.7% male-to-female ratio.
The results showed that individuals with increased baseline SBP experienced a 3.0 mm Hg greater reduction in SBP with HEPA vs sham, while those with normal baseline SBP showed minimal variations. Reductions in DBP were small and not statistically significant. The study concluded that cardiovascular risk was possible in low pollution environments, and even modest BP reduction can occur in cardiovascular risk by 4 to 9%. The observed 3 mm Hg SBP decrease among individuals with elevated BP was consistent with earlier trials and meta-analyses.
Limitations included unexplained variation in PM2.5 and PNC reductions, unpredictability about the time course of BP changes, insufficient indoor temperature data for all homes, limited generalizability, and potential concerns about long-term acceptability.
After considering the lack of hazards and cardiovascular benefits, this study recommended HEPA filtration for vulnerable groups, specifically those with increased BP or those living near high-traffic highways. Further research is required in more hypertensive, diverse, and hot-climate populations to determine which subgroups derive the greatest benefit.
Reference: Brugge D, Eliasziw M, Thanikachalam M, et al. Effect of HEPA filtration air purifiers on blood pressure: a pragmatic randomized crossover trial. J Am Coll Cardiol. 2025. doi:10.1016/j.jacc.2025.06.037
