High Efficiency Particle Air (HEPA) filters not only clean the air — according to Danish researchers — they may significantly improve cardiovascular health.

Researchers measured the effect of air filtration on 21 non-smoking couples aged 60 to 75 in two 48-hour periods. In one 48-hour period, a HEPA filter was used in the couples' homes. In the other period, a filter was not present.

The size of the indoor air particles and their concentrations were monitored throughout.

The aim of the study was to determine the microvascular function of the study participants — when the HEPA filter was in place and when it wasn't. This was measured through finger sensors, as well as blood and urine samples that identified inflammatory markers in the blood, oxidative stress and clotting issues.

The researchers discovered that when the HEPA filters were used, they removed about 60 per cent of the particles in the homes. As well, the finger sensors picked up an 8.1 per cent improvement in blood flow on average.

"Our main finding was a significant improvement in the function of small finger blood vessels after reduction of indoor air particles. This effect most likely indicates a general improvement in the function of the inner lining of small vessels, including those supplying the heart," said Professor Steffen Loft of the Institute of Public Health in Copenhagen, in a release.

"This suggests that indoor air filtration represents a feasible means of reducing cardiovascular risk."

Poor functioning of the small blood vessels indicates an increased risk of heart problems, according to the authors.

The researchers now want to explore the link between airborne particles and their impact on cardiovascular health. They theorize that fewer particles in the bloodstream means less inflammation — one of the precursors to heart problems.

The study is published in the second February issue of the American Journal of Respiratory and Critical Care Medicine.