The level of air pollution is increasing globally. While developed countries are trying to curb air pollution through laws and regulations, many low- and middle income countries do not have the infrastructure in place to control this problem which is actually a consequence of urbanization and economic development.
Air pollution comes with serious health consequences that may lead to chronic diseases such as respiratory, cardiovascular, and even neurological disorders. According to a World Health Organization (WHO) report, it can cause about 2 million premature deaths worldwide.
Fine particles in the air we breathe are especially dangerous. In this post, I review the recent research studies on the cardiovascular effects of air pollution.
What is fine particulate matter?
According to the US Environmental Protection Agency (EPA)
Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods of time. Some particles are large or dark enough to be seen as soot or smoke. Others are so small that individually they can only be detected with an electron microscope. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes. Particles less than 10 micrometers in diameter (PM10) pose a health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as “fine” particles and are believed to pose the greatest health risks. Because of their small size (approximately 1/30th the average width of a human hair), fine particles can lodge deeply into the lungs.
What are the cardiovascular effects of particulate matter in the air?
In the US alone, one of three people is at risk of health risks of air pollution, especially PM2.5, particles which are mostly generated by vehicular traffic.
This 2007 study published in the New England Journal of Medicine followed up 1,816 women of postmenopausal age. The participants were monitored for cardiovascular events (e.g. heart attacks, stroke) for a medial follow-up time of 6 years. Data on air pollution on their areas of residence were also collected. The results of the study showed that the risk for cardiovascular event is highly correlated o the concentrations of PM2.5. Furthermore, the risk increases with women who are overweight or obese.
Other studies show that the closer your place of residence is to major roads with high volume traffic, the higher is your risk for cardiovascular problems.
In one study published in the journal Circulation in 2007, German scientists monitored 4494 adults aged 45 to 74 years old for at least five years. The study participants were checked for coronary artery calcification (CAC) as well as the distance of their residences to major. The results show that people who live close to the road (100 m or less) have a much higher risk for CAC that those who live further away (more than 100 m). CAC is an indication of atherosclerosis. The study concludes that “long-term residential exposure to high traffic is associated with the degree of coronary atherosclerosis.” Again, the pollution culprits in the air are the traffic-related PM2.5.
More recent studies (Epidemiology, 2009) show residential exposure to pollution in urban areas is associated with peripheral arterial disease especially among women. This trend was observed in urban areas in Germany as well as in the US.
So how do particles in the air affect our cardiovascular health?
This study on 48 Boston residents hospitalized for heart attacks, unstable angina or coronary artery disease suggests that particles in air interferes with the heart’s ability to conduct electrical signals. This was observed even if the particulate matter concentration is below National Air Quality Standard thresholds.
The American Heart Association and the American College of Cardiology recommend that some heart patients, particularly those who have had a heart attack, delay driving for two to three weeks after leaving the hospital and avoid driving in heavy traffic because of the stress it creates. This recent study that it’s not only stress but also traffic pollution that presents danger to the patients while driving.
Long-term exposure to air pollution has also been observed to alter blood coagulation function and thereby increasing the risk for deep vein thrombosis. The culprits in this case are even finer particles PM10 which seem to shorten prothrombin time. Each increase of 10 µg/m3 in PM10 was associated with a 70% increase in DVT risk. The DVT risk increase associated with air-pollution levels was smaller in women and limited to those who were not using oral contraceptives or hormone therapy at the time of diagnosis.
Coming next in this CVD-pollution series:
- Pollution and health problems in different countries.
- How to avoid pollution exposure.
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