New study shows link between long-term exposure

image: A large-scale epidemiological study in China identified links between long-term exposure to ambient air pollution and metabolic-associated fatty liver disease (MAFLD).
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Credit: Journal of Hepatology

Amsterdam, December 6, 2021Metabolism-associated fatty liver disease (MAFLD) is a growing global health challenge and represents a substantial economic burden. A large-scale epidemiological study in China identified links between long-term exposure to ambient air pollution and MAFLD. These links are exacerbated by unhealthy lifestyles and the presence of central obesity, report scientists from the Journal of hepatology, the official journal of the European Association for the Study of the Liver, published by Elsevier.

The incidence of MAFLD has increased steadily since the 1980s, currently affecting a quarter of the world’s population and a majority of patients with adult diabetes, and constitutes a significant global burden. In Asia, MAFLD increased to 40% between 2012 and 2017. Formerly known as non-alcoholic fatty liver disease (NAFLD), it can progress to end-stage liver disease such as cirrhosis and liver cancer, liver transplantation and liver related death.

Accumulating animal studies have shown that breathing air pollutants can increase the risk of MAFLD. For example, exposure to fine particles can trigger a non-alcoholic steatohepatitis (NASH) -like phenotype, alter hepatic glucose metabolism, and promote hepatic fibrogenesis.

“The MAFLD epidemic corresponds to the environmental and lifestyle changes that have occurred alongside rapid industrialization around the world, especially in many Asian countries,” said lead researcher Xing Zhao, PhD, West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, Sichuan, China. “A growing number of studies suggest 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 and metabolic syndrome. However, the epidemiological 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.

Investigators conducted an epidemiological study on the potential role of ambient air pollution in the risk of MAFLD in approximately 90,000 adults in China based on the China Multi-Ethnic Cohort (CMEC) baseline survey. , a prospective cohort that recruited nearly 100,000 participants in southwest China from 2018 to 2019. CMEC collected information on participants, including socio-demographic data, lifestyle and health-related history, through verbal interviews conducted by trained personnel and then evaluated anthropometry, biological samples (blood, urine and saliva) and imaging data.

Researchers have found that long-term exposure to ambient air pollution may increase the risks of MAFLD, especially in men, smokers and alcohol drinkers, and those who consume a high-fat diet. . Unhealthy lifestyle behaviors and excessive accumulation of fat in the abdominal area can exacerbate the harmful effects.

“Our findings add to the growing evidence for the detrimental effects of environmental pollution on metabolic function and associated organs,” commented Dr Zhao and his co-investigators. However, physical activity does not appear to alter the associations between air pollution and MAFLD. We suggest that future studies explore whether the timing, intensity and form of physical activity may mitigate the effects. harmful air pollution.

Investigators suggest that air pollution be recognized as a modifiable risk factor for MAFLD. High-risk populations should be aware of the air quality in the areas where they live and plan their activities to minimize their exposure to air pollution.

In a accompanying editorial, Massimo Colombo, MD, Hôpital San Raffaele, Liver Center, Milan, Italy, and Robert Barouki, MD, PhD, University of Paris, Unit Inserm T3S, Paris, France, noted that the assessment of the main determinants of mortality in the world by the WHO has shown that global pollution tops the list, ranking higher than smoking, alcohol consumption and major infectious diseases, and that air pollution, the most common component critical of global pollution, is likely to be responsible for millions of deaths per year worldwide.

“Better characterization of the liver exposome should improve prevention and precautionary advice,” commented Dr Colombo and Dr Barouki. “Indeed, while physical activity combined with a healthy diet constitutes the main pillar in the fight against morbidities associated with metabolic syndrome, including MAFLD, the findings that environmental pollution could exacerbate the risk of MAFLD could offer new clues to refine the advice of these patients, for example. for example by limiting the exposure of populations at risk to high pollution outdoor environments, as recommended for patients with severe asthma. It also provides an added incentive for policymakers to speed up efforts to comply with WHO air pollution guidelines and limits, as many cities in Europe and around the world are still well above these limits. “

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