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

By Priyanjana Pramanik, MSc.Reviewed by Danielle Ellis, B.Sc.Sep 3 2024

Unhealthy lifestyles account for over 37% of NAFLD cases, with air pollution further amplifying risk, study finds

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

Their results indicate that while 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 may affect more than 32% of people around the world, 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 for NAFLD risk, allowing medical professionals to identify people more likely to develop it. However, being exposed to air pollution and leading an unhealthy lifestyle can increase the chances of developing NAFLD.

Previous studies on this subject are limited. They have focused on East Asian populations and examined exposure to fine particulate matter as a driver of NAFLD risk, but their findings are inconclusive. Focusing on the joint association between lifestyle and air pollution can help medical professionals and policymakers design effective strategies to prevent this disease.

About the study

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

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

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

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

The main outcome measured was the incidence of NAFLD, which was tracked through hospital records. The analysis involved statistical models to estimate NAFLD risk based on air pollution exposure, 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 analyses were conducted to ensure the robustness of the findings.

Findings

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

Specifically, unhealthy lifestyle factors, such as poor diet, lack of physical activity, and smoking, were the leading contributors to NAFLD, accounting for 37.18% of the risk. Air pollution also significantly contributed to NAFLD risk, with high pollution levels increasing the likelihood of the disease.

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

The study revealed that participants with both high air pollution exposure and unhealthy lifestyles were at the greatest risk of developing NAFLD, with hazard ratios indicating 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 underscore the importance of addressing both environmental and lifestyle factors in preventing 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 primary contributors to NAFLD risk. The study found that the combination of high pollution exposure and an unhealthy lifestyle led to the highest risk. These findings emphasize the importance of adopting a healthy lifestyle to mitigate the impact of air pollution on liver health.

The study's strengths 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 the exclusion of certain cases due to missing data. Additionally, the study population was primarily of European descent, 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.