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"Safe" air pollution levels can elevate heart attack risk within one hour

In a startling revelation, a recent study conducted by scientists at Columbia University suggests that even levels of air pollution considered “safe” under current guidelines could trigger heart attacks. 

More concerning still, the onset of these heart attacks can occur within just an hour of exposure to polluted air. This alarming evidence has led to increasing calls from experts for stricter air quality standards.

Nitrogen dioxide 

The study was focused on nitrogen dioxide (NO2), a harmful pollutant mainly emitted by cars. The researchers meticulously tracked NO2 levels across nine US cities over a span of 15 years. By comparing this data with hospitalization rates due to heart attacks in the same areas, the scientists were able to discern a worrying correlation.

As the concentration of NO2 in the air increased, so did the risk of heart attacks. Alarmingly, this increased risk manifested itself just 60 minutes after a spike in NO2 levels. 

Notably, the risk of heart attacks increased even when NO2 levels were lower than the current US national standard of 100 parts per billion (ppb). This threshold signifies that out of every billion units of air, 100 units of NO2 are considered safe.

These standards align with those set by the World Health Organization and UK air standards, which state that the hourly concentration of NO2 should not exceed 200 micrograms per cubic meter of air (µg/m³). 

A level of 100 ppb NO2 is equivalent to 191 µg/m³. As per UK regulations, the hourly levels of toxic NO2 should not breach this limit more than 18 times a year. Nonetheless, air quality tracking tools reveal that this limit is consistently surpassed in certain areas of London.

Dire consequences 

In a paper published in the journal Environment International, the researchers wrote: “Our findings suggest that current hourly standards may be insufficient to protect cardiovascular health.'” This statement underscores an alarming reality – despite being considered “safe,” current air pollution levels could have dire consequences for public health.

Existing studies have repeatedly linked air pollution, particularly from traffic, to heart attacks. Tiny pollutants, so minuscule that they infiltrate deep into the lungs and bloodstream, can constrict blood flow to the heart. This forces the heart to work harder than usual, thus increasing the risk of heart problems. 

However, the specific timeframe within which the risk of heart problems increases after exposure to pollution, and the duration of this elevated risk, remain unknown.

To investigate, the team analyzed data on the hourly NO2 concentrations for cities in New York state from 2000 to 2015. This data was coupled with hospitalization information for 8.9 million people, of whom 350,000 suffered a heart attack. It was discovered that the average hourly NO2 concentrations were around 23.3 ppb.

Millions of deaths each year

Disturbingly, each 10 ppb increase in NO2 concentration corresponded to a 0.2 percent rise in the risk of heart attacks. Moreover, the risk of a heart attack was found to be highest within the first hour of exposure, when it increased by 0.21 per cent. 

The elevated risk persisted for six hours following spikes in NO2 levels in all cities, and even lasted up to 24 hours in some cases.

With around 100,000 Britons and 800,000 Americans suffering heart attacks annually, the implications of these findings are vast. As evidence mounts regarding the health risks of air pollutants – which have been linked not only to heart disease but also to dementia and cancer – the World Health Organization is urging countries to implement more stringent measures. 

The stakes are incredibly high; the UN agency estimates that poor air quality leads to seven million deaths annually and slashes millions of healthy years off lives.

“Safe” levels of air pollution

Defining “safe” levels of air pollution is a complex task because it is increasingly apparent that even small amounts of pollutants can have negative impacts on health. 

Regulatory bodies such as the U.S. Environmental Protection Agency (EPA), the European Environment Agency (EEA), and the World Health Organization (WHO) set standards for what they consider safe levels of various pollutants. However, these levels are under constant review as new scientific data emerges.

In the case of NO2, exposure can exacerbate respiratory conditions and lead to increased susceptibility to respiratory infections. PM2.5 can be inhaled deep into the lungs, potentially causing severe health issues such as heart attacks, strokes, and premature death.

However, increasingly, studies such as the one from Columbia University mentioned in the previous article suggest that even these “safe^ levels may not be entirely safe. The study found that heart attack risk increases even below the current standards for NO2. These findings, along with similar research, may lead to calls for stricter air quality standards.

Air pollution can vary greatly from one location to another, and even from one hour to the next. In areas with heavy traffic or industrial activity, for example, levels of pollutants like NO2 can spike well above the ‘safe’ limits, posing immediate health risks to people in those areas. This variation in air quality can make it challenging for individuals and communities to protect themselves from pollution, particularly if they lack access to real-time air quality data.

Moreover, certain groups, including children, older people, and people with pre-existing health conditions, are more vulnerable to the effects of air pollution. Therefore, even “safe” levels of pollution may pose significant risks for these individuals. As our understanding of the impacts of air pollution continues to evolve, so too must the standards that govern air quality.


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