Rationale: Exposure to particulate matter is associated with risk of cardiovascular events, possibly through endothelial dysfunction, and indoor air may be most important.

Objectives: We investigated effects of controlled exposure to indoor air particles on microvascular function (MVF) as the primary endpoint and biomarkers of inflammation and oxidative stress as secondary endpoints in a healthy elderly population.

Methods: A total of 21 nonsmoking couples participated in a randomized, double-blind, crossover study with two consecutive 48-hour exposures to either particle-filtered or nonfiltered air (2,533–4,058 and 7,718–12,988 particles/cm³, respectively) in their homes.

Measurements and Main Results: MVF was assessed noninvasively by measuring digital peripheral artery tone after arm ischemia. Secondary endpoints included hemoglobin, red blood cells, platelet count, coagulation factors, P-selectin, plasma amyloid A, C-reactive protein, fibrinogen, IL-6, tumor necrosis factor-α, protein oxidation measured as 2-aminoadipic semialdehyde in plasma, urinary 8-iso-prostaglandin F_2α, and blood pressure. Indoor air filtration significantly improved MVF by 8.1% (95% confidence interval, 0.4–16.3%), and the particulate matter (diameter < 2.5 μm) mass of the indoor particles was more important than the total number concentration (10–700 nm) for these effects. MVF was significantly associated with personal exposure to iron, potassium, copper, zinc, arsenic, and lead in the fine fraction. After Bonferroni correction, none of the secondary biomarkers changed significantly.

Conclusions: Reduction of particle exposure by filtration of recirculated indoor air for only 48 hours improved MVF in healthy elderly citizens, suggesting that this may be a feasible way of reducing the risk of cardiovascular disease.