Human hearts and polluted air

By Dr. Liji Thomas, MDDec 16 2019

Air pollution is injurious to our lungs and our blood vessels, according to many previous studies. However, a new study published on December 16, 2019, in the Journal of Physiology, says that the human heart responds to air pollution in more or less the same way as that of sea-living creatures. This confirms a new dimension to marine ecology, the study of the marine ecosystem, in helping to improve human health as well as adding motivation to curb the destruction of earth’s climate and environment.

It is estimated that within the UK, about 11,000 people die of heart disease (heart attacks, cardiac failure or cardiac arrest due to insufficient blood supply to the heart) caused specifically due to air polluted with particulate matter (PM). PM denotes the presence of tiny particles of solid matter or droplets in the air that can harm human health. Among these particles of various sizes, those with a diameter of 2.5 micrometers (PM2.5) are the smallest and the most dangerous. The UK has not achieved control of the level of this type of PM so far, in accordance with EU standards.

The study

In the current study, the researchers examined the compounds in polluted air that affect vertebrate hearts. They looked especially at some compounds that attach to the surface of PM, called polycyclic aromatic hydrocarbons (PAH), which are known to be related to the injurious effects of air pollution on the heart.

What are PAHs?

PAHs are a class of chemicals that are found in coal, petrol and crude oil, as well as being produced during the burning of fossil fuels, woods, tobacco and garbage. They are hydrocarbons, which means they contain only hydrogen and carbon, but are made up of several closed ring structures. Humans can be exposed to PAHs in various commonplace ways, such as asphalt fumes, smoke from wood fires and fossil fuels, and vehicle exhaust, as well as marijuana or cigarette fumes. Grilling and charring foods can also increase the PAH content, as does the use of liquid smoke seasonings.

PAHs and heart health

The harmful effects caused by air pollution in humans is a relatively new research topic, but the link between PAH and heart disease in marine animals has been long established, as well as the underlying reason.

For instance, after the Exxon Valdez tanker spilled 11 million gallons of crude oil in the Alaskan waters off Prince William Sound, 30 years ago, the marine ecology of that region suffered such serious damage that it has still not recovered.

11 years later, the Deepwater Horizon drilling rig explosion in the waters of the Gulf of Mexico, just off the coast of Louisiana, released an estimated 4.9 million barrels (about 640 million liters) of oil, in the largest marine spill in history.

Deepwater Horizon well site, Louisiana. Image Credit: Breck P. Kent / Shutterstock

During the rehabilitation period, studies showed that many marine species were adversely affected, including birds, turtles, dolphins and whales. A telling study in 2014 reported finding distinctive heart defects in the developing embryos of two species of tuna and one amberjack species, due to their exposure to PAH from the spill. The defects affected the ability of the heart to contract properly and occurred with high consistency across all the species.

PAHs affect the autonomic nerve supply of the heart, causing it to beat slower and weaker. The mechanism is via the blockade of important ion channels that allow potassium and calcium ions to pass through them, mediating the excitation-contraction coupling that is all-important in achieving heart contraction. As a result, the adult fish also has a permanently damaged heart, impacting its ability to swim fast or long. This in turn makes it more vulnerable to an early death.

The dosage of exposure is also important. At very low levels (such as 1-10 micrograms/liter), the oil caused an increased number of the fish to die before reaching maturity. At higher levels, the fish embryos developed heart failure and died soon after they changed into the larval or free-swimming forms.

Implications

The researchers in the current study point out that the human heart develops and functions in much the same way as that of these marine life forms. As a result, what happened to the tuna embryos could well be happening to mankind, as a result of PAHs and PM in the air.

Researcher Holly Shiels says, “Pollution affects all of us living on Planet Earth. Due to the conserved nature of cardiac function amongst animals, fish exposed to PAH from oil spills can serve as indicators, providing significant insights into the human health impacts of PAHs and PM air pollution.”

The study would thus play a major role in the attempts made by medical experts to shape governmental thinking on air pollution norms. This alone can force public policy to adopt WHO norms for air pollution limits.

Cardiologist Jeremy Pearson, of the British Heart Foundation, concurs: “We know that air pollution can have a hugely damaging effect on heart and circulatory health, and this review summarises mechanisms potentially contributing to impaired heart function. Reducing air pollution is crucial to protecting our heart health.”