Long-term exposure to air pollution and poor lifestyle choices increase the risk of non-alcoholic fatty liver disease

Unhealthy lifestyles account for more than 37% of NAFLD cases, with air pollution further increasing the risk, study finds

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In a recent study published in BMC Public Health, researchers investigated how the combined effects of lifestyle factors and ambient air pollution affect the risk of developing non-alcoholic fatty liver disease (NAFLD).

Their findings suggest that although unhealthy lifestyles and exposure to air pollutants over long periods significantly increase the risk of NAFLD, unfavorable lifestyle factors may influence the effect of air pollution.

Background

NAFLD can affect more than 32% of people worldwide, and this common liver disease is known to cause other serious conditions such as hepatocellular carcinoma and cirrhosis. Cases of NAFLD are increasing, making it a public health priority.

There may be a genetic basis to the risk of NAFLD, allowing medical professionals to identify people who are more likely to develop it. However, exposure to air pollution and an unhealthy lifestyle can increase the chances of developing NAFLD.

Previous studies on this topic are limited. They focused on East Asian populations and examined exposure to fine particulate matter as a risk driver of NAFLD, but their findings are inconclusive. Focusing on the combination of lifestyle and air pollution can help medical professionals and policy makers devise effective strategies to prevent this disease.

About the study

In this study, the researchers used data from the UK Biobank, a large population-based study that included over 500,000 participants aged 37-73. Participants provided information about their demographics, lifestyle, and health through questionnaires, interviews, and physical examinations.

For this analysis, individuals with pre-existing liver conditions, cancer, alcohol dependence, or missing data were excluded, leaving 417,025 participants.

Researchers used data from the European Cohort Study of Air Pollution Effects (ESCAPE) to assess exposure to air pollution, including fine particulate matter (PM2.5, PM10) and nitrogen oxides (NO2, NOx).

They also assessed lifestyle factors, including physical activity, diet, smoking, alcohol intake, sedentary time, and sleep duration, combining them into a lifestyle score.

The primary outcome measured was the incidence of NAFLD, which was tracked through hospital records. The analysis involved statistical models to estimate the risk of NAFLD based on exposure to air pollution, lifestyle factors, and their combined effects.

Various covariates, including age, sex, socioeconomic status, and environmental factors, were adjusted to account for potential confounding variables. Sensitivity analyzes were performed to ensure the robustness of the results.

Results

Researchers found that 4,752 participants (1.14%) developed non-alcoholic fatty liver disease (NAFLD) over an average follow-up of 12.4 years. The risk of developing NAFLD was higher among participants exposed to elevated levels of air pollution (eg, nitrogen dioxide, particulate matter) and those with unhealthy lifestyles.

Specifically, unhealthy lifestyle factors, such as poor diet, lack of physical activity, and smoking, contributed the most to NAFLD, accounting for 37.18% of the risk. Air pollution is also a major contributor to the risk of NAFLD, with high levels of pollution increasing the likelihood of developing the disease.

The overall air pollution score (weighted average of all pollutants) showed an almost 10% association with NAFLD, and among individual air pollutants, NO2 (10.19%) and NOx (8.18%) had the highest roles.

The study showed that participants with high air pollution exposure and unhealthy lifestyles were at the greatest risk of developing NAFLD, with hazard ratios showing more than double the risk compared to those with low pollution exposure and healthy lifestyles.

The results also indicated that air pollutants and lifestyle factors interact, meaning that their combined effect on NAFLD risk is greater than the sum of their individual effects. These findings highlight the importance of addressing both environmental and lifestyle factors to prevent NAFLD.

Conclusions

The study highlights that long-term exposure to air pollutants and an unhealthy lifestyle significantly increase the risk of developing NAFLD.

Lifestyle factors, such as poor diet and lack of physical activity, were the major contributors to the risk of NAFLD. ​​​​The study found that the highest risk resulted from the combination of high pollution exposure and an unhealthy lifestyle. These findings highlight the importance of adopting a healthy lifestyle to mitigate the impact of air pollution on liver health.

Strengths of the study include its large, population-based design and standardized assessment of exposure to air pollution. However, limitations include reliance on self-reported lifestyle data, potential recall bias, and exclusion of some cases due to missing data. In addition, the study population was mainly of European origin, which may limit the generalizability of the findings.

Future research should explore the impact of air pollution and lifestyle factors in more diverse populations and investigate the long-term effects of these risk factors on liver health.