Increased Risk of Non-Alcoholic Steatohepatitis in Patients With Inflammatory Bowel Disease: A Population-Based Study

Background and objective The global health burden of inflammatory bowel disease (IBD) stems from its increasing incidence over the years. Comprehensive studies on the topic hypothesize that IBD plays a more dominant in the development of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH). In light of this, we conducted this study with the aim of assessing the prevalence and risk factors of developing NASH in patients who have had a diagnosis of ulcerative colitis (UC) and Crohn’s disease (CD). Methodology A validated multicenter and research platform database of more than 360 hospitals from 26 different healthcare systems across the United States from 1999 to September 2022 was utilized for conducting this study. Patients aged 18-65 years were included. Pregnant patients and individuals diagnosed with alcohol use disorder were excluded. The risk of developing NASH was calculated using a multivariate regression analysis to account for potential confounding variables including male gender, hyperlipidemia, hypertension, type 2 diabetes mellitus (T2DM), and obesity. A two-sided p-value <0.05 was considered statistically significant, and all statistical analyses were performed using R version 4.0.2 (R Foundation for Statistical Computing, Vienna, Austria, 2008). Results A total of 79,346,259 individuals were screened in the database and 46,667,720 were selected for the final analysis based on the inclusion and exclusion criteria. Using multivariate regression analysis, the risk of developing NASH among patients with UC and CD was calculated. The odds of having NASH among patients with UC was 2.37 (95% CI: 2.17-2.60, p<0.001). Similarly, the odds of having NASH were high in patients with CD as well, at 2.79 (95% CI: 2.58-3.02, p<0.001). Conclusion Based on our findings, patients with IBD have an increased prevalence and higher odds of developing NASH after controlling for common risk factors. We believe that a complex pathophysiological relationship exists between both disease processes. Further research is required to establish appropriate screening times to enable earlier disease identification and thereby improve patient outcomes.


Introduction
Non-alcoholic steatohepatitis (NASH) and benign steatosis are on the histologic spectrum of non-alcoholic fatty liver disease (NAFLD), a clinicopathological condition. NASH is defined as hepatic steatosis and inflammation with hepatocyte injury, Mallory hyaline inclusions, and mixed lymphocytic and neutrophilic inflammatory infiltrate in perivenular areas with or without fibrosis [1]. On the other hand, inflammatory bowel disease (IBD) comprises Crohn's disease (CD) and ulcerative Colitis (UC). While CD is characterized by colonic transmural inflammation with skip lesions, UC is a chronic inflammatory condition characterized by relapsing and remitting episodes of inflammation limited to the colon's mucosal layer.
Multiple studies have shown strong associations between IBD and NAFLD. In a study by Bessissow et al., the prevalence of NAFLD was 33.6% in patients with IBD [2]. Also, Sourianarayanane et al. found that NAFLD had an incidence of 8.2% in patients with IBD when compared to patients without NAFLD [3]. In another study by Elchert et al., the overall prevalence of NASH in CD patients was 0.34% compared to 0.08% in the general population [4]. Many possible pathophysiological hypotheses have been proposed to explain this association, including disease-specific risk factors, such as chronic inflammation, steroid exposure, druginduced hepatotoxicity, malnutrition, and alteration of gut microbiota [5].
NASH is the second leading cause of liver transplantation in the US [6]. Hence, it is critical to identify the risk factors for NASH so that the overall disease burden can be reduced. Our study focuses on understanding the prevalence and risk of developing NASH in patients with IBD by taking into account the confounding factors, including male gender, hyperlipidemia, hypertension, type 2 diabetes mellitus (T2DM), obesity, UC, and CD.

Study design
Our cohort's data were obtained using a validated, multicentered, and daily-updated database called Explorys (

Patient selection
A cohort of patients with a SNOMED-CT diagnosis of NASH between 1999 and May 2022 was identified. Patients aged 18-65 years were included. Pregnant patients and individuals diagnosed with alcohol use disorder were excluded.

Covariates
Confounding factors associated with NASH were identified and collected if SNOMED-CT diagnoses were available. These were male gender, hyperlipidemia, hypertension, T2DM, and obesity.

Statistical analysis
The prevalence of NASH, UC, and CD was calculated by dividing the respective number of subjects by the total number of subjects in the Explorys database. To account for confounding from the covariates listed above, we conducted 256 searches to explore every probability, with UC and CD representing one of the variables. A univariate analysis was conducted initially for all the variables, followed by a multivariate analysis. Statistical analysis was performed using R version 4.0.2 (R Foundation for Statistical Computing, Vienna, Austria, 2008), and a two-sided p-value <0.05 was considered statistically significant for all analyses. Multivariate analysis was performed to adjust for multiple factors, including male gender, hyperlipidemia, hypertension, T2DM, obesity, UC, and CD.

Results
A total of 79,346,259 individuals were screened in the database and 46,667,720 were included in the final analysis as per the inclusion and exclusion criteria. There were 34,200 people with NASH with a prevalence rate of 73 per 100,000 ( Table 1). The prevalence of NASH was highest among patients with hypertension, hyperlipidemia, and obesity (66%, 64%, and 62% respectively).

Discussion
The development of NASH, both in patients with or without a diagnosis of IBD, has been strongly associated with T2DM, hypertension, and metabolic syndrome by multiple lines of evidence [7]. A significant proportion, around 30%, of patients with IBD have been observed to have altered liver inflammatory markers, suggesting the presence of extra-intestinal manifestations in the liver and biliary tract [5]. In fact, primary sclerosing cholangitis (PSC), an autoimmune condition, is observed in 70% of patients with IBD [8]. These findings have led to an increased interest in investigating the association between IBD and NASH. Our study aimed to examine this relationship based on a database of 360 hospitals from 26 healthcare systems in the United States. The results showed that patients with IBD had an increased prevalence of developing NASH compared to those without IBD. The study by Abenavoli et al. (2022) aimed to shed light on the complex interplay between gut microbiota and two increasingly prevalent diseases, NAFLD and IBD [9]. It is worth mentioning that NAFLD encompasses a range of conditions, ranging from simple fatty liver to NASH, which can eventually lead to liver cirrhosis and hepatocellular carcinoma [10]. Several previous studies have demonstrated gut dysbiosis in NAFLD and IBD, each with distinct underlying mechanisms [11][12][13][14]. Despite numerous studies supporting a positive association between IBD and NAFLD, a clear and well-established common pathogenesis has yet to be determined, although several emerging hypotheses exist [15]. In effect, they point to a potential interplay between factors such as increased intestinal permeability, changes in gut microbiota, endotoxemia, oxidative stress-induced inflammation, and genetic susceptibility [9,16]. Herein, the overproduction of conjugated bile acids due to gut dysbiosis may contribute to the development of NAFLD when they are returned to the liver [17]. The excessive production of reactive oxygen species (ROS) by Kupffer cells and alteration in mitochondrial DNA demonstrate the slowed progression of NAFLD to NASH, hepatocellular necroinflammation and fibrosis, and lastly carcinoma. Jarmakiewicz-Czaja et al. have also discussed the role of glucocorticoids, a widely used treatment for IBD, as well as other drugs, in developing NAFLD in IBD patients [18]. While investigations into the possible gut-liver immune axis are ongoing, further clinical studies are required to solidify the evidence base for this relationship.
The results of our study endorse previous findings in the literature, notably the most recent ones. Ritaccio et al. conducted a retrospective study of 1,672 IBD patients to examine the prevalence of NAFLD and the progression of NAFLD-related fibrosis [19]. The study found a prevalence of 12.4% for NAFLD, with most patients displaying stable liver fibrosis index at the five-year follow-up. The results were compared to earlier studies from 1992 and 1998, which were limited in terms of their ability to measure the outcomes with the parameters employed adequately. Despite these limitations, the results were consistent with a previous estimate of approximately 20% [20,21]. In a study by Elchert et al., the prevalence of NASH in patients with and without CD was assessed, and the overall prevalence of NASH in CD patients was 0.34% compared to 0.08% in the general population [4]. Magri et al. conducted an observational study involving 178 patients with IBD and found that 40.4% of patients had NASH with varying degrees of steatosis [22]. Another observational study by Principi et al. found a prevalence of 28% of NAFLD in a sample of 465 IBD patients [23]. Lastly, a monocentric cross-sectional study by Hoffmann et al. involving 694 IBD patients found that 48% of patients with CD and 44% of patients with UC had NAFLD, defined by increased echogenicity on liver ultrasound [24]. Despite these concurring results, the influence of the study design employed, sample size, and data analysis on the strength of evidence of these studies still needs to be determined.
A recent study by Yen et al. evaluated the prevalence and risk factors of NAFLD in a retrospective cohort of 81 patients with IBD [25]. Controlled attenuation parameter (CAP) technology with a Fibroscan® was employed for liver stiffness measurement and abdominal ultrasound for the screening program. The study showed that 29.6% of IBD patients were diagnosed with NAFLD based on a CAP value of ≥248 dB/m. However, the results were not statistically significant (p=0.761). The univariate analysis of CD as a risk factor also showed statistically insignificant results (p=0.870). Another study by Mancina et al. employed the same advanced diagnostic liver evaluation using CAP in a cohort of 95 IBD patients and 53 healthy volunteers as a control group [26]. The study's results revealed higher fat content and liver stiffness in IBD patients compared to the control group (CD: 238 ±48 dB/m; UC: 246 ±44 dB/m; controls: 214 ±49 dB/m). The multivariate analysis showed that UC was associated with a higher risk of developing mild steatosis (OR: 4.80; 95% CI: 1.64-14.04) and moderate to severe steatosis (OR: 7.49; 95% CI: 2.36-23.76). These results correlate favorably with the findings of our study that showed a two-to three-fold increased risk of developing NASH.
Several meta-analyses have examined the association between NAFLD and IBD [27,28,29]. The most recent meta-analysis, conducted by Zamani et al., employed a rigorous study design and methodology [29]. The study was based on a systematic search of multiple databases, with the final analysis including 44 studies with 14,947 patients: 19 studies were from Europe, 18 were from the Americas, four were from the Western Pacific, two from South-East Asia, and one from the Middle East. The meta-analysis found that the pooled prevalence of NAFLD in IBD patients was 30 , which was consistent with the findings of previous studies. The difference in prevalence observed in our study may be attributed to several factors, including the examination of each IBD disease individually, the exclusion criteria employed, the larger sample size, the diagnostic methods used for the diagnosis of IBD and NAFLD, and the potential impact of different levels of steatosis on the results. Furthermore, the meta-analysis found that IBD patients were 1.96 times more likely to develop NAFLD compared to controls (OR: 1.96; 95% CI: 1.13-3.4), based on a comparison of four studies with a total of 3,884 subjects. The study also found that CD was associated with a 1.16-fold increased risk of NAFLD compared to UC (OR: 1.16; 95% CI: 0.93-1.44).
Individuals diagnosed with IBD are at an elevated risk of readmission and death due to the co-occurrence of NAFLD. They are more vulnerable to metabolic syndrome, given the recent advancements in the treatment of IBD. With the growing global incidence of both NAFLD and IBD, driven by the Westernization of global culture, it is crucial to implement screening protocols to identify IBD patients at risk of NAFLD and use noninvasive methods for early detection of fatty liver. This is particularly important given the findings of our study, which highlight the increased risk of NAFLD in IBD patients in a large cohort.
Our study has several limitations that must be considered. Primarily, other potential confounding factors, such as medication exposure and other chronic liver or biliary diseases, were not considered. In addition, the study did not take into account the different grades of liver steatosis. Furthermore, the study utilized a database from the United States, which limits the generalizability of its results to other populations given the differences in phenotypes of IBD. Finally, the retrospective, population-based design of the study limits our ability to establish a causal relationship between IBD and NASH.

Conclusions
Multiple studies have indicated an association between IBD and the development of NAFLD. Our study, which examined a database of 360 hospitals in the US, found that individuals with IBD were twice as likely to develop NASH compared to those without IBD. Chronic systemic inflammation seen in patients with IBD, eventually leading to excessive production of ROS and alteration in mitochondrial DNA, is believed to be the underlying link. The underlying mechanisms of this relationship remain unknown, and further research is needed to gain a more comprehensive understanding of the molecular basis of this relationship. This study represents a significant contribution to the field, as it is the first study of its kind with a large sample size and provides a strong foundation for future studies to further explore the causality of this relationship through experimental designs such as randomized controlled trials and large-scale cohort studies.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.