Effects of long-term indoor air purification intervention on cardiovascular health in elderly: a parallel, double-blinded randomized controlled trial in Hong Kong.

Ambient fine particulate matter (PM) is a leading environmental risk factor globally, and over half of the associated disease burden are caused by cardiovascular disease. Numerous randomized controlled trials (RCT) have investigated the short-term cardiovascular benefits of indoor air purifiers (IAPs), but major knowledge gaps remain on their longer-term benefits. In this 1-year, randomized, double-blinded, parallel controlled trial of 47 elderly (n = 24; n = 23) aged ≥70 years, true-purification reduced household PM levels by 28% and maintained lower exposure throughout the year compared to the sham-purification group. After 12 months of intervention, a significant reduction of diastolic blood pressure was found in the true-purification versus sham-purification group (-4.62 [95% CI: -7.28, -1.96] mmHg) compared to baseline measurement prior to the intervention, whereas systolic blood pressure showed directionally consistent but statistically non-significant effect (-2.49 [95% CI: -9.25, 4.28] mmHg). Qualitatively similar patterns of associations were observed for pulse pressure (-2.30 [95% CI: -6.57, 1.96] mmHg) and carotid intima-media thickness (-10.0% [95% CI: -24.8%, 4.7%]), but these were not statistically significant. Overall, we found suggestive evidence of cardiovascular benefits of long-term IAPs use, particularly on diastolic blood pressure. Evidence on other longer-term cardiovascular traits is less clear. Further trials with larger sample sizes and long-term follow-up are needed across diverse populations to evaluate the cardiovascular benefits of IAPs.