A study conducted by the Faculty of Medicine at The Chinese University of Hong Kong (CU Medicine) has proved that high concentration of Particulate Matter (PM2.5) led to an 8% increase in the carotid intima media thickness (IMT), which is a surrogate of early atherogenic process. This reflects that the risk of stroke and heart attack is increased by over 40%. Study findings have been published in the International Journal of Epidemiology¹. 

Atherosclerotic diseases, accounting for the majority of the cardiovascular and cerebrovascular diseases, are the leading causes of death worldwide. In addition to traditional risk factors such as obesity, hypertension, dyslipidemia, diabetes mellitus, tobacco use and physical inactivity, exposure to high levels of PM2.5 has been shown to be associated with cardiovascular morbidity and mortality in ample epidemiological studies, but grossly underestimated.

Air Pollution and COVID-19 Interaction

The toll on patients with heart disease and stroke during the COVID-19 pandemic increased substantially, and interaction of COVID-19 with air pollution has been implicated. A joint statement in January 2021 by international organisations², including the World Heart Federation, the American College of Cardiology, the American Heart Association and the European Society of Cardiology, called for urgent action to reduce air pollution and adopt effective preventive measures for controlling the heavy air pollution impact on cardiovascular disease, stroke, diabetes and respiratory diseases. These chronic conditions are known to raise a person’s risk of experiencing some of the more severe consequences of COVID-19.

PM2.5 air pollution triggers low grade pulmonary inflammation and thus systemic vascular inflammation-induced atherosclerosis

The research team studied the data from 1,656 adults, collected from 1996 to 2007, who were living in modernising China (e.g. Hong Kong, Macau, Pun Yu in Guangdong, Yu County in Shanxi and the 3-Gorges Territories). Ultrasound was used to check the participants’ brachial flow-mediated dilatation (FMD) and carotid intima media thickness (IMT), both being prognostic surrogates predictive of heart attack and stroke.

PM2.5 parameters were computed from satellite sensors and the population exposure to PM2.5 was estimated. Findings showed that those in the upper PM2.5 tertile, compared with the lower tertile, have significantly worse FMD but an 8% increase in carotid IMT. Details are as follows:

*FMD was calculated as the difference between the maximum diameter postrelease of occlusion and the average baseline diameter, which was expressed as a percentage relative to the average baseline diameter. A normal healthy FMD response was accepted as 7–10%. Higher value reflects better vascular health.

According to a study report conducted by researchers in the Netherlands, this 8% IMT difference is comparable to a 41% increase in stroke and 43% increase in heart attack over a follow-up period of 2-7 years³, and comparable with the kind of difference seen between diabetic and non-diabetic adults, with significant long term health implication.

Professor Timothy Chi Yui KWOK, Professor of the Department of Medicine and Therapeutics at CU Medicine, stated, “PM2.5 air pollution can trigger low grade pulmonary inflammation and thus lead to a systemic vascular inflammation-induced atherosclerosis. Changes in the incidence and mortality of cardiovascular diseases and stroke after interventions usually need a longer while, say 10-20 years, to be apparent and accordingly are very costly. On the other hand, changes in the prognostic surrogates including IMT and FMD after intervention can be witnessed in a few months, proposing a promising approach for evaluation of the PM2.5-related atherosclerosis prevention programme.”

Interventional Preventive Strategy for PM2.5 Air Pollution

To overcome challenges caused by air pollution and cardiovascular diseases, the research team will launch a randomised placebo controlled interventional study. Subjects (including workers exposed to a highly polluted environment, for example bus / taxi driver, cook or building site worker) will be randomised to take a pulmonary anti-inflammatory agent (montelukast) or dummy placebo for six months, and their atherosclerosis surrogate markers (FMD and IMT) will be compared.

Dr Kam Sang WOO, cardiologist and Adjunct Professor of the Department of Medicine and Therapeutics at CU Medicine, added, “This interventional study will further prove the correlation between air pollution and cardiovascular diseases. It will also provide a strong foundation for future interventions to prevent the disease. In addition to carrying out actions to improve air quality, we hope the impact of atherosclerosis on patients as well as its burden on medical services will be reduced.”

The interventional study is a collaboration with the Chongqing Medical University. For those who are interested, please register at https://bit.ly/3a9rbDz.

1 The impact of particulate matter air pollution (PM2.5) on atherosclerosis in modernizing China: a report from the CATHAY study. International Journal of Epidemiology (2020)

https://academic.oup.com/ije/advance-article/doi/10.1093/ije/dyaa235/6012822?login=true

2 Leading cardiovascular organizations call for urgent action to reduce air pollution
https://www.world-heart-federation.org/news/leading-cardiovascular-organizations-call-for-urgent-action-to-reduce-air-pollution/

3 Bots ML, Hoes AW, Koudstaal PJ, Hofman A, Grobbee DE. Common carotid intima-media thickness and risk of stroke and myocardial infarction: The Rotterdam Study. Circulation 1997; 96:1432–37