Liver disease and early death caused by air pollution, study warns

CHENGDU, China — Living near a busy road can lead to liver disease, according to new research. A large-scale study has identified a link between the deadly condition and local levels of air pollution. Even small hikes in pollution increased local people’s risk of fatty liver disease by almost a third, according to scientists in China.

An estimated 100 million Americans have non-alcoholic fatty liver disease (NAFLD) and, according to studies, fumes from traffic and industry are fueling soaring numbers of cases.

“Our findings add to the growing evidence of ambient pollution’s damaging effects on metabolic function and related organs,” says lead investigator Dr. Xing Zhao of the West China School of Public Health and West China Fourth Hospital of Sichuan University in a media release.

The findings come from health and residency records of around 90,000 people in China. Other information the team used included blood, urine, and saliva samples, imaging data, and information on sociodemographic and lifestyle habits.

Air pollution’s link to several diseases

Liver disease incidences have soared in the last four decades, currently affecting a quarter of the global population. NAFLD is the ​​most common form of liver disease in children. The NAFLD mortality rate in the U.S. is also increasing. NAFLD, also called metabolic-associated fatty liver disease (MAFLD), may trigger cirrhosis or liver cancer. Some patients require a liver transplant.

“The [metabolic-associated fatty liver disease] MAFLD epidemic corresponds to environmental and lifestyle changes that have occurred alongside rapid industrialization worldwide, especially in many Asian countries,” Dr. Zhao explains.

“A growing number of studies have suggested that ambient air pollution, which is the biggest environmental problem caused by industrialization, may increase the risk of metabolic disorders such as insulin resistance and dyslipidemia, and related diseases such as type 2 diabetes mellitus and metabolic syndrome. However, epidemiologic evidence for the association was limited, so we conducted this research to improve our understanding of the effects of air pollution on human health and also to help reduce the burden of MAFLD.”

Particulate matter significantly increases disease risk

The study found a person’s chances of having the illness rose with greater exposure to particles and gases formed by the burning of fossil fuels. For instance, for every density increase in PM2.5s (fine particulate matter) of 10 micrograms per cubic meter of air, the risk increased by 29 percent. The tiny particles lodge in the lungs and make blood stickier, triggering inflammation. The same small climb in nitrogen dioxide levels — produced mainly by diesel vehicles — made liver disease 15 percent more likely.

Men, smokers, drinkers, and those who consume a high-fat diet appear to be most prone, suggesting unhealthy lifestyles may exacerbate the harmful effects.

“However, physical activity did not seem to modify the associations between air pollution and MAFLD. We suggest that future studies explore whether the timing, intensity, and form of physical activity can mitigate the harmful effects of air pollution,” Dr. Zhao notes.

Apparently, traffic fumes in towns and cities largely wipe out the benefits of walking, jogging, or cycling. The researchers propose that governments should recognize air pollution as a modifiable risk factor for liver disease. Populations at high risk should be aware of the air quality in the areas where they live and plan activities to minimize exposures.

Air pollution continues to be a global health threat

Pollution tops the list in the World Health Organization’s (WHO’s) major determinants of mortality. It ranks higher than smoking, drinking, and major infectious diseases and is likely to be responsible for millions of deaths per year. Liver specialists Prof. Massimo Colombo of San Raffaele Hospital in Italy and Prof. Robert Barouki, a biochemist at Paris University, believe pollution should fall into the same category as asthma in terms of health threats.

“Indeed, whereas physical activity together with a healthy diet stand as a primary pillar in the fight against metabolic syndrome associated morbidities, including MAFLD, the findings that ambient pollution could exacerbate MAFLD risk might offer new clues to refining the counseling of these patients, for instance by restricting exposure of risk populations to open air settings at high level of pollution, as is recommended for patients suffering from severe asthma,” Colombo and Barouki say.

“It also constitutes an additional incentive for decision makers to speed up the efforts to conform with the WHO guidelines and limits on air pollution, as many cities in Europe and worldwide are still well above those limits.”

Long-term exposure to pollution is a leading global health concern. Even low concentrations could cause tens of thousands of early deaths every year in the U.S.

The study is published in the Journal of Hepatology. The new findings also confirm animal experiments showing breathing in air pollutants leads to liver disease.

South West News Service writer Mark Waghorn contributed to this report.

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