Air pollution is a leading cause of global ill health, responsible for between 4.9 and 8.8 million deaths each year, largely from cardiovascular disease. Exposure to fine particulate matter has been shown to affect the heart and circulation in various ways, including damaging the inside walls of blood vessels, increasing blood pressure and causing abnormal heart rhythms. Tobacco smokers and those who use solid fuels for cooking/heating are at particular risk.
Recent years have seen an explosion of interest in indoor air purifiers, many of which are marketed with health claims that include the ability to reduce cardiovascular disease risk. Until now, however, there has been no rigorous assessment of the cardiovascular health benefits of indoor air purifiers. To address this, researchers from NDPH and the Chinese University of Hong Kong have published the most comprehensive systematic review and meta-analysis to date of all studies on the cardiovascular effects of indoor air purifiers. The results are published in Science of the Total Environment.
The meta-analysis (pooling of results from different studies) included 14 randomised controlled trials conducted between 2008 and 2020, in four different countries (USA, Canada, Denmark and China). In total, these studies involved 794 participants. The combined studies assessed both air purifiers that use electrostatic technology to capture dust, and those that pump air through a filter. Besides blood pressure, these studies measured biomarkers of cardiovascular disease risk, including inflammatory proteins, oxidative stress markers and reactive hyperaemia index (which measures the ability of blood vessels to dilate following a restriction in circulation).
- Overall, the studies indicated that using air purifiers led to a small reduction in systolic blood pressure* by an average of -2.28 mmHg. However, there was no decrease in diastolic blood pressure*.
- Air purifiers with High Efficiency Particulate Air (HEPA) filters were associated with a modest reduction in pulse pressure* and a slight improvement in reactive hyperaemia index.
- Overall, no significant improvements were found in the level of inflammatory proteins (C-reactive protein, interleukin-6 and fibrinogen) or oxidative stress markers (malondialdehyde and 8-isoprostane).
The researchers also assessed the quality of the studies included in the analysis. They concluded that the overall certainty of evidence remained low, and the small effects, if any, reported in the 14 trials did not substantiate the claim that indoor air purifiers can improve cardiovascular health outcomes.
Lead author Dr Peter KaHung Chan (NDPH) said: ‘Most of the included studies had severe limitations, including small sample sizes and a short duration. Future, higher-quality studies using larger sample sizes, longer intervention periods, and more diverse populations are urgently needed to clarify the cardiovascular benefits of air purifier interventions. In the meantime, claims on such benefits should be more cautious.’
Co-author Associate Professor Hubert Lam (NDPH) added: ‘Most previous trials were constrained by funding and scalability. With the increasing need for mitigation strategies against air pollution, we hope to see greater investment for more robust evidence on this topic.’
*Systolic blood pressure is the blood pressure in the arteries when the heart contracts. Diastolic blood pressure is the blood pressure in your arteries when your heart relaxes. Pulse pressure is the difference between your systolic and diastolic blood pressure.