Traffic-related air pollution causes liver damage

Recent evidence indicates that even modest exposure to traffic-related air pollution could harm the liver and potentially increase the likelihood of developing metabolic-associated fatty liver disease (MAFLD). 

Researchers at the University of Technology Sydney (UTS) set out to investigate how fine particulate matter – collected from urban roadways – can undermine liver health over time. 

While air pollution is typically associated with respiratory risks, this research suggests its effects may extend far beyond the lungs.

“We think of air pollution as being harmful to people’s lungs, but it has a broader impact on health including on the liver,” said lead author Hui Chen, a professor at UTS. 

What is fatty liver disease?

Fatty liver disease, also known as hepatic steatosis, is the world’s most prevalent liver disorder, characterized by an overaccumulation of fat in liver cells. 

In its advanced stages, fatty liver can lead to inflammation, cirrhosis, cancer, or even organ failure. A key reason the liver is so vulnerable is because it plays central roles in detoxifying the blood, regulating glucose, and producing essential molecules the body needs to function.

“The liver is critical for metabolism. It clears toxins, regulates blood sugar, and produces essential vitamins and proteins, among many other functions. If the liver isn’t functioning properly, it can leave people feeling tired and unwell due to disrupted metabolism,” Chen explained.

How pollution particles infiltrate the liver

The study examined the effects of tiny particulate matter, specifically PM2.5, which is smaller than 2.5 microns – about 3% the diameter of a human hair. Because of its minuscule size, PM2.5 bypasses many of the body’s natural filters when inhaled. 

“When we inhale air pollution, the very tiny particles known as PM2.5 enter the bloodstream through the lungs. The liver, which filters toxins from the blood, then accumulates these substances, which can include heavy metals such as arsenic, lead, nickel and zinc,” said Chen. 

Over time, this accumulation may strain the organ and jeopardize overall metabolic health.

Pollution exposure and fatty liver

World-renowned liver specialist Professor Jacob George, director of the Storr Liver Center and a co-author of the study, researches the causes of liver diseases and cancer. 

Professor George pointed out that “around one in three Australian adults has fatty liver disease, and it is more common in those who are overweight or have diabetes.” 

Although unhealthy dietary habits, physical inactivity, and excess alcohol consumption are well-established contributors, these latest findings highlight the added role that chronic exposure to traffic pollution may play. 

This insight emphasizes the complexity of fatty liver disease, which likely results from a combination of lifestyle, genetic, and environmental elements.

Cumulative effects on the liver

The researchers exposed mice to 10 micrograms of traffic-related PM2.5 each day – a dose they say reflects typical human exposure levels in busy urban areas, such as major roads in Sydney. 

Key markers of liver health, including inflammation and fibrosis (scar tissue formation), plus changes in liver sugars and fats, were tracked at intervals of four, eight, and twelve weeks.

After four weeks, the liver showed few notable changes. After eight weeks, however, clear disruption in normal metabolic function was observed.

By twelve weeks, significant changes emerged, including higher levels of inflammation and scarring, altered sugar storage, and increased harmful fats.

“The effect was cumulative. At four weeks we didn’t see much change, but by eight weeks there was disruption to the normal metabolic function of the liver and by 12 weeks we could see significant changes,” explained first author Dr. Min Feng, a medical doctor and PhD candidate in the UTS Faculty of Science.

How air pollution alters liver chemistry

The presence of PM2.5 appeared to spur immune cells to cluster in the liver, leading to inflammation and scar tissue formation. 

In addition, the liver’s processing of fats ramped up, leading to more potent forms of lipids – like triglycerides, diacylglycerols, and ceramides – while simultaneously storing less sugar for energy. 

On a molecular level, researchers discovered changes in 64 liver proteins, many of which correlate with fatty liver, immune dysfunction, or cancer-related processes.

“Previous research has shown that exposure to heavily polluted air is associated with liver disorders, however this study reveals even low levels can cause harm. It suggests there is no safe level of exposure to traffic-derived air pollution,” said Chen.

Mitigating health risks of traffic pollution

The researchers recommend that people limit their exposure to traffic-related air pollution by avoiding peak-hour commutes, taking less congested routes when possible, and closing car windows with air recirculation mode in dense traffic. They also suggest considering masks if traveling through highly polluted areas. 

Such steps may help reduce the accumulation of PM2.5 in the bloodstream and minimize any subsequent stress on the liver.

While further research is needed to explore how medication or therapeutic interventions might mitigate this pollution-driven liver damage, these findings add a new dimension to how air pollution can impact health. 

By demonstrating that even small doses of PM2.5 can compromise liver function over time, the study broadens the discussion of environmental hazards. Fatty liver disease and other related conditions may be more intricately tied to daily life in polluted urban settings than previously recognized.

As a next step, the researchers plan to investigate potential treatments, such as targeted pharmaceuticals or lifestyle modifications, that could bolster the liver’s resilience against pollution. 

While lifestyle factors – such as a healthy diet, exercise, and reduced alcohol intake – remain central to preventing fatty liver, evidence now points to tackling environmental exposures as well.

The study is published in the Journal of Environmental Sciences.

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