Could air pollution increase heart attack risk?

A study has found that exposure to ultrafine particles of pollution may be a trigger for heart attacks. The research demonstrated that 6 hours after exposure to this type of pollution, there was an increase of 3–6% in nonfatal heart attacks.

There is a clear link between air pollution and various health conditions, with children particularly susceptible to harm. According to the World Health Organization (WHO), pollution causes one-third of all deaths from stroke, lung cancer, and heart disease.

Ultrafine particles (UFPs) are of particular interest to researchers with evidence that they might be key to the negative health impacts of pollution, particularly in respiratory health. The reason is their very small size, their large surface area relative to their mass, and their ability to enter the bloodstream.

In urban areas, the combustion of petrol or diesel in cars and other vehicles — with their exhaust fumes entering the surrounding environment — is the predominant source of UFPs.

As a consequence, some cities around the world are trying to significantly reduce the number of vehicles able to drive into their centers. According to a study in the journal Environment International, this reduces not only air pollution but also noise pollution and greenhouse gases; it also increases more active forms of travel, such as walking and cycling.

The most recent study, which appears in Environmental Health Perspectives, specifically looked at the effects of UFPs on heart health. While researchers have suspected that there is a relationship between UFPs and heart health, scientists could not clearly demonstrate the link before this study.

According to Kai Chen, Ph.D., assistant professor at Yale School of Public Health in New Haven, CT, and the study’s first author:

“This study confirms something that has long been suspected — air pollution’s tiny particles can play a role in serious heart disease. This is particularly true within the first few hours of exposure. Elevated levels of UFP are a serious public health concern.”

Annette Peters, director of the Institute of Epidemiology at Helmholtz Center Munich in Germany and co-author of the paper, adds, “We were the first to demonstrate the effects of UFP on the health of asthmatics in an epidemiological study in the 1990s. Since then, approximately 200 additional studies have been published. However, epidemiological evidence remains inconsistent and insufficient to infer a causal relationship.”

The authors believe that inconsistency in past findings is because of the many different ways scientists can measure UFPs. For example, different groups might look at their size, their surface area, or their quantity. Furthermore, results change depending on how researchers define UFPs. The authors of the latest study accounted for many of these variables in their research.

To determine the relationship between UFPs and nonfatal heart attacks, the team looked at the data from air pollution monitoring sites in the city of Augsburg in Germany between 2005 and 2015.

They then compared this with data on nonfatal heart attacks in the city during the same period, adjusting their findings to account for a variety of other factors that might also cause an increase in nonfatal heart attacks.

The researchers found that there was a correlation between increased UFPs and the rate of nonfatal heart attacks, particularly in the first few hours following the increase in particles. This increase in heart attacks ranged from just over 3% to almost 6%, depending on how they measured the particles.

The researchers could only look at nonfatal heart attacks as information about the timing of fatal heart attacks was not available. However, they note that in another study that looked at daily levels of UFPs, the authors found no difference between fatal and nonfatal heart attacks.

“This represents an important step toward understanding the appropriate indicator of ultrafine particles exposure in determining the short-term health effects,” Prof. Chen comments, adding, “as the effects of particle length and surface concentrations were stronger than the ones of particle number concentration and remained similar after adjustment for other air pollutants.”

To take the study further, Prof Chen explained that future analyses would look at the combined hourly exposures to both air pollution and extreme temperature.

“We will also identify vulnerable subpopulations, regarding pre-existing diseases and medication intake,” he concludes.