Bedroom Air Purification and Home Blood Pressure

Air pollution, particularly fine particulate matter (PM2.5), is an important risk factor of cardiovascular diseases, including elevated blood pressure and hypertension 1. It has been reported that for every 10 µg/m3 increase in short-term PM2.5 exposure, the pooled risk ratio for cardiovascular mortality is 1.0090 (95% confidential interval CI: 1.0074 to1.0106) 2. Long-term exposure to outdoor PM2.5 has been associated with elevated blood pressure, with a 10 µg/m3 increase in concentration linked to a 4% higher risk of hypertension (OR = 1.04, 95% CI: 1.01 to 1.07) 3. In a meta-analysis of 20 long-term and 5 short-term studies 4, there were significant associations between exposure to PM2.5 and hypertension, with an odds ratio (OR) of 1.05 (95% CI: 1.01 to 1.09) and 1.10 (95% CI: 1.06 to 1.13), respectively. In addition, the effect of PM2.5 exposure varies across various stages of hypertension for the risk of mortality. In a recent nationwide, individual-level, time-stratified and case-crossover study of more than 2.1 million hypertension-related deaths in China, the attributable fraction of deaths to PM2.5 rose from 0.65% in uncomplicated primary hypertension to 2.12% in hypertensive heart disease and 2.65% in hypertensive kidney disease and to 3.20% in hypertensive heart and kidney disease 5. Outside and indoor PM2.5 levels are correlated, particularly at high levels of PM2.5 exposure. High-efficiency indoor air filters, or personal air cleaners (PACs) have been proposed as an intervention to decrease indoor PM2.5 exposure. In a meta-analysis of 10 randomized controlled trials, PAC use yielded an absolute and relative PM2.5 reduction of 20.9 ± 18.2 µg/m3 and 55.9 ± 17.0%, respectively, and was associated with a significant reduction in mean systolic blood pressure by −3.94 mmHg (95% CI: −7.00 to −0.89, p = 0.01), but a non-significant difference in mean diastolic blood pressure by −0.95 mmHg (95% CI: −2.81 to 0.91, p = 0.32) 6. Similarly, in a latest meta-analysis of 17 studies involving 880 participants, the use of PACs was associated with a relative reduction of 59.8% (ranging from 23% to 82%) indoor PM2.5 exposure and a mean systolic/diastolic blood pressure reduction of −2.35 (95% CI: −4.50 to −0.20) /−0.81 mmHg (95% CI: −1.86 to 0.24) 7. A few trials have been published since the systematic review (Table 1). Several key issues regarding the implementation of PACs for hypertension management, however, remain unaddressed, such as the optimal intervention intensity, proper device placement (bedroom or living room), timeframe of use (daytime, nighttime, or whole day), duration of benefit, effectiveness on ambulatory and home blood pressure and so on. Mean/ Median age (years) Brugge D (2025) 8 Xia X (2024) 9 Xia X (2023) 10 In this issue of the Journal, Brook and colleagues evaluated effects of a single PAC on indoor PM2.5 levels and home blood pressure over a 4-week bedroom-based intervention in a group of low-income older adults (n = 33) 12. With double-blind, randomized, cross-over design, the study participants were benefited from the single PAC with a lower bedroom PM2.5 concentration (active PAC vs. sham PAC: 1.3 ± 1.5 vs. 8.3 ± 12.8 µg/m3, p < 0.001) and 24-hour personal exposure (5.1 ± 4.6 vs. 12.4 ± 15.6 µg/m3, p < 0.001). Home blood pressure was not different between the intervention and control groups, with a mean difference of −1.43 / −0.56 mmHg for systolic (p = 0.161) / diastolic blood pressure (p = 0.266). However, a tendency of benefit for home blood pressure reductions by using PACs was observed in older participants with older age, body mass index, and baseline systolic blood pressure. The current study is rigorously designed and implemented, demonstrating significant public health relevance. First, the study participants were chosen from low-income older-adults residential facility, lived within 200 meters of major highway, which were prone to be affected by PM2.5. Second, using a single-bedroom PAC rather than multiple units enhances the cost-effectiveness of the intervention. The primary outcome was innovatively assessed by home blood pressure monitoring, which better avoids masked effect by clinical measurement, offers improved reproducibility, and more closely reflects daily life blood pressure. The finding of this study on single-bedroom PAC and home blood pressure extends the potential use of the cost-effective, accessible PACs for stable management of hypertension, particularly among susceptible individuals. However, the impact of PACs on blood pressure reduction remains inconclusive, which may be associated with the ambient air pollution levels across study settings. In a pilot study of 20 adults with self-reported hypertension living in New York City public housing 11, participants were randomized to active versus sham PACs for 14 days, with home blood pressure monitoring in the morning. There was a non-significant trend of a lower morning systolic blood pressure for active versus sham group (129.6 ± 8.9 vs. 134.6 ± 9.6 mmHg, p = 0.25), as well as in the change from baseline (5.67 ± 10.08 vs. 2.18 ± 9.16 mmHg, p = 0.25) 11. These null findings may be associated with the lack of measurement of indoor PM2.5 concentrations and the lack of difference in outdoor PM2.5 concentrations between the active and sham conditions (5.50 ± 0.20 vs. 5.75 ± 0.10 µg/m3, p = 0.24). In the current study, the authors noted that the modest home blood pressure-lowering effect might be attributed to the potential impact of COVID-19. COVID-19 hindered participant recruitment and study progress. The lower-than-expected sample size might have also contributed to the increased heterogeneity in home blood pressure monitoring and instability in the study observations. Many participants wore facemasks due to the COVID-19 mandates, which were probably unable to assess the participants’ inhalation of PM2.5 accurately and contributing to the negative findings. Nonetheless, a 4-week of intervention may be insufficient, and the home blood pressure response to environmental changes may require a longer duration to manifest. The impact of PACs on blood pressure may be prominent in specific populations. In a larger randomized crossover trial (n = 154), individuals living nearby highways reported significant benefits among participants with elevated brachial systolic blood pressure (≥120 mmHg) 8. In this trial, high-efficiency particulate arrestance (HEPA) filtration was associated with a 2.8 mmHg mean reduction in systolic blood pressure (p = 0.03), with a net between-group difference of 3.0 mmHg in favor of active filtration (p = 0.04). No significant benefit was observed for diastolic blood pressure nor in participants with a systolic blood pressure below 120 mmHg 8. Hypertension and air pollution are two major public health challenges worldwide. As a cost-effective and low-risk intervention, air purification warrants further investigation regarding its potential role in the management of hypertension. Several key considerations should be addressed in future studies. First, participants’ characteristics, including blood pressure status, hypertension, use of antihypertensive medications, and cigarette smoking status, should be taken into consideration. Second, the blood pressure lowering effect should be examined across various pollution gradients to investigate whether the air pollution levels have influence on the benefit. Third, blood pressure measurement should be more comprehensive and standardized, incorporating home and ambulatory blood pressure monitoring, and wearable blood pressure measurement devices to improve the assessment of participants’ blood pressure throughout day and night as well as long-term intervention effects. Fourth, seasonal variation and ambient (indoor and outdoor) temperature should be accounted for, given their independent association with blood pressure 1, 13. Fifth, the optimal timeframe and adherence of PACs use should be evaluated 8, 12 which may be associated with the device noise and potential sleep disturbance. Finally, in addition to PM2.5 measurements, information on other surrounding environmental factors should be collected, such as humidity, noise pollution, and individual behaviors including mask use, window opening and cooking habits 3, 14 to better characterize the context of PACs use. Jia-Bo Zhu prepared the first draft of the manuscript. Xiao-Fei Ye critically revised the manuscript. All authors reviewed and gave the final approval. The authors have nothing to report. The authors declare no conflicts of interest.