Prevalence and Risk Factors of Metabolic Associated Fatty Liver Disease in China: A Cross-Sectional Study

Metabolic associated fatty liver disease (MAFLD) is a new denition for liver disease associated with known metabolic dysfunction. Based on new diagnostic criteria, we aim to investigate its prevalence and risk factors in Chinese. Methods This cross-sectional study was implemented on 139170 subjects who participated in health examination. Results (males: females: and before in males in (36.2% vs. however signicantly lower after 65 (28.2% vs. 33.0%, P<0.001). The prevalence in different female menopausal status (premenopause, perimenopause, postmenopause) was 6.1%,16.8%, and 30.2%, in BMI groups (underweight, normal, overweight and obese), it was 27.4% and Proportions of abnormal metabolic in were higher than those in non-MAFLD so as the proportion of elevated alanine aminotransferase (ALT) (42.5% vs. P<0.001). Prevalence of metabolic syndrome (MS), dyslipidemia, and hyperuricemia in MAFLD group (53.2%, 80.0%, and was signicantly higher than that in non-MAFLD group (10.1%, 41.7%, and 16.8%). Logistic regression revealed that age, BMI, circumference, ALT, triglyceride, fasting glucose, uric acid and platelet count were associated with MAFLD. and 60994 females (43.8%). All the participants completed comprehensive anthropometric measurements and clinical examination including abdominal ultrasonography, the collection of fasting blood and urine samples. Repeat examinations of the same person were recognized by their unique health examination ID, and only one data set were randomly involved in the study. Exclusion criteria were those with incomplete data; younger than 18 years old; history of malignancy; history of oophorectomy or hysterectomy; history of liver surgery or nephrectomy. MAFLD suffer a high prevalence of MS, dyslipidemia, and hyperuricemia. The presence of MAFLD and MS interact with each other and they may be the risk factor of each other. Moreover, non-obese people also suffer from MAFLD, and it’s also closely related to metabolic disorders. We also conrmed the high proportion of elevated ALT in people with MAFLD. Multiple metabolic disorders especially obesity should be paid great attention to improve the prevention and management of MAFLD. More researches are still needed to determine the potential mechanisms of the occurrence of MAFLD, as well as further relationship and causality between MAFLD and multiple metabolic disorders, which would provide crucial implications for the prevention and treatment of MAFLD.


Background
Metabolic associated fatty liver disease (MAFLD), formerly called nonalcoholic fatty liver disease (NAFLD), is a new de nition for liver disease associated with known metabolic dysfunction, which is the most common chronic liver disease around the world. It was reported that NAFLD affected 24% of the adult population around world, which has posed threat to human health [1]. NAFLD is generally considered to be closely related to obesity and multiple metabolic disorders and it can vary from hepatic steatosis to steatohepatitis, brosis or cirrhosis [2], it is regarded as the hepatic manifestation of multisystem metabolic dysfunction [3]. Previously, the diagnosis of NAFLD was an exclusive diagnosis [3], however, since researches has progressed, NAFLD was found to be derived from the potential state of multiple metabolic dysfunction with complex pathophysiological characteristics, and the high prevalence in the general population makes it common to be co-existed with other liver diseases, which indicates that the exclusive criteria can no longer meet current requirement for the diagnosis of the disease. Hence, in recent international expert consensus, "MAFLD" was considered to be a better description of the liver disease associated with known metabolic dysfunction [4], and a set of positive diagnostic criteria were therefore released quickly [5], so that MAFLD can be accurately, comprehensively and easily diagnosed. With the patient population being somewhat different from that of NAFLD, disease characteristics can be better manifested through the patient population diagnosed by new diagnostic criteria. Therefore, this cross-sectional study aims to investigate the prevalence and risk factors of MAFLD based on new diagnostic criteria, to better elucidate the association between MAFLD and multiple metabolic disorders, so as to provide a more accurate reference for the management and prevention of MAFLD.

Study population
This cross-sectional study used data of a general Chinese population who took part in the health examination at the Quality Control Center of Health Examination in Chongqing (China), which is also known as the Health Management Center of the First A liated Hospital of Chongqing Medical University, from January 2015 to September 2018, most of the participants are urban residents. Our study involved 139170 participants which including 78176 males (56.2%) and 60994 females (43.8%). All the participants completed comprehensive anthropometric measurements and clinical examination including abdominal ultrasonography, the collection of fasting blood and urine samples. Repeat examinations of the same person were recognized by their unique health examination ID, and only one data set were randomly involved in the study. Exclusion criteria were those with incomplete data; younger than 18 years old; history of malignancy; history of oophorectomy or hysterectomy; history of liver surgery or nephrectomy. The study was approved and supervised by The Ethics Committee of The First A liated Hospital of Chongqing Medical University (approval number: 2019-141).

Anthropometric measurements and clinical examination
Blood pressure and anthropometric parameters including height, weight and waist circumference were measured in standardized procedures by trained examiners. Body mass index (BMI) was calculated as follows: BMI (kg/m 2 ) = weight (kg)/height squared (m 2 ). Venous blood samples of all participants were collected after at least 8 hours of fasting and were analyzed by standard procedures in the laboratory of First A liated Hospital of Chongqing Medical University, which was certi ed by the College of American Pathologists (CAP No.: 7215494). Abdominal ultrasound was performed using ultrasound scanners (Aplio500, Toshiba Medical Systems, Japan or HD11XE, Philips Medical Systems, U.S.A). All the abdominal ultrasonography was performed and evaluated by experienced ultrasonographist in the Quality Control Center of Health Examination. Since the diagnosis of MAFLD does not involve the assessment of alcohol consumption and hepatitis virus, here we didn't include the two examinations in our study. Disease histories were checked in the health examination results of each participant. All data were recorded in the electronic medical record system of the Quality Control Center of Health Examination in Chongqing.

Diagnosis of MAFLD
The diagnosis of MAFLD is based on the ultrasonically diagnosed hepatic steatosis and the presence of one of the following three criteria: overweight or obesity (de ned as BMI≥23 kg/m 2 in Asians), type 2 diabetes mellitus, or metabolic dysregulation. Metabolic dysregulation is de ned by the presence of at least two following metabolic risk abnormalities: 1) Waist circumference≥90/80 cm in Asian men and women; 2) Blood pressure ≥130/85 mmHg or speci c drug treatment; 3) Plasma triglycerides ≥ 1.70 mmol/L or speci c drug treatment; 4) Plasma HDL-cholesterol <1.0 mmol/L for men and <1.3 mmol/L for women or speci c drug treatment; 5) Prediabetes (i.e., fasting glucose levels 5.6 to 6.9 mmol/L, or 2-hour postload glucose levels 7.8 to 11.0 mmol or HbA1c 5.7% to 6.4%; 6) Plasma high-sensitivity C-reactive protein (hs-CRP) level >2 mg/L; 7) Homeostasis model assessment (HOMA)-insulin resistance score ≥2.5 [5]. The diagnosis of hepatic steatosis on ultrasound was based on the wildly used criteria [6].
De nitions BMI groups of underweight (<18.5 kg/m2), normal (≥18.5 kg/m2, <23.0 kg/m2), overweight (≥23.0 kg/m2, <25.0 kg/m2) and obese (≥25.0 kg/m2) were categorized based on the BMI criteria for Asians made by WHO [7]. Metabolic syndrome (MS) was de ned in accordance with the criteria by Joint Statement [8], which was based on the presence of at least 3 of the following components: 1) Elevated waist circumference (≥90 cm for men and ≥80 cm for women); 2) Elevated triglycerides (≥1.70 mmol/L) or the drug treatment for elevated triglycerides; 3) Reduced HDL-C (< 1.0 mmol/L for men and <1.3 mmol/L for women) or the drug treatment for reduced HDL-C; 4) Elevated blood pressure (≥130/85 mm Hg) or the drug treatment for the hypertension; 5) Elevated fasting glucose (≥5.6 mmol/L) or the drug treatment for elevated glucose. Dyslipidemia was de ned according to the guidelines for the prevention and treatment of dyslipidemia in Chinese adults [9], as follows: the total cholesterol level of ≥5.2 mmol/L; the LDL-C level of ≥3.4 mmol/L; the HDL-C level of <1 mmol/L and the triglyceride level of ≥1.7 mmol/L. Hyperuricemia was de ned as the uric acid level of ≥416 μmol/L for men or ≥357 μmol/L for women [10]. Menopausal status was de ned as premenopausal period (≤45 years old), perimenopausal period (45-54 years old) and postmenopausal period (≥55 years old) according to the mean menopausal period for Chinese female population [11,12]. Elevated liver enzymes was de ned as ALT> 35IU/L and AST> 40IU/L [13].

Statistical analysis
All the continuous variables were tested by normality testing and were described by medians (interquartile range) and proportions. Mann-Whitney U test was performed to compare continuous variables due to their non-normal distribution. For categorical variables, the chi-square test was performed to compare between different variables. Speci c prevalence of different age, BMI and female menopausal status groups and their 95% con dence intervals (CIs)were calculated. Binary logistic regression analysis was performed to explore the related risk factors of MAFLD. Odds ratios (ORs) and their 95% CIs were nally calculated. Binary logistic regression was performed with RStudio version 4.0.1, and other analysis was performed with SPSS 25. A two-tailed p-value < 0.05 was considered statistically signi cant.

General data of 139170 participants.
Of the 139170 Chinese adults enrolled in the study, 78176 subjects (56.2%) were males and 60994 (43.8%) were females. Baseline characteristics of study subjects were showed in Table 1. Compared to people without MAFLD, those with MAFLD were older, predominantly male, had higher values of body mass index (BMI), waist circumference, blood pressure, fasting glucose, total cholesterol, triglyceride, low-density lipoprotein cholesterol (LDL-C), albumin, total bilirubin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), creatinine, uric acid, white blood cell count (WBC), red blood cell count (RBC), hemoglobin, platelet count, and hematokrit (HCT), and had lower value of high-density lipoprotein cholesterol (HDL-C) (P < 0.05). Compared to males with MAFLD, females with MAFLD tended to be older, had higher values of systolic pressure, fasting glucose, total cholesterol, HDL-C LDL-C, and platelet count.  Fig. 1. The prevalence tended to rise with the increase of age and then decrease, with the peak total prevalence being reached at 34.5% in the age range of 55-59. For females, the prevalence of MAFLD rose slowly between the age range of 18-49, however it rose steeply after 50 years, which was consistent with the appearance of perimenopausal period, and peaked at 35.2% in the age range of 65-69, while for males, the prevalence rose rapidly between the age of 18-39, then rose slowly after 40 years and it peaked at 42.5% in the age range of 50-54, revealing that the peak prevalence appeared earlier in males than that in females.  (Fig. 3).

Related risk factors of MAFLD and association between MAFLD and metabolic disorders.
The proportion of abnormal metabolic features in MAFLD group were all signi cantly higher than those in non-MAFLD group (P < 0.001, Table 2). The proportion of elevated liver enzymes especially elevated ALT was also signi cantly higher in people with MAFLD than that in people without MAFLD (42.5% vs. 11.1% for elevated ALT, χ 2 value = 16944.455, P < 0.001). For people with MAFLD, they are more likely to have multiple metabolic disorders, and the prevalence of MS, dyslipidemia and hyperuricemia in people with MAFLD were all signi cantly higher than that in people without MAFLD ( Fig. 4)  value = 29779.866, P < 0.001). In the binary logistic regression, our results revealed that eight variables are closely related to MAFLD, including age, BMI, waist circumference, ALT, triglyceride, fasting glucose, uric acid and platelet count (Table 4). Among them, triglyceride, BMI and fasting glucose were found to have the most signi cant association with MAFLD, with the highest OR values of 1.776, 1.476 and 1.403, respectively.

Association Between Non-obese People And Ma d
Among the non-obese population, the prevalence of MAFLD was 11.5% (males:16.4% & females: 6.9%). The proportions of abnormal metabolic features and elevated liver enzymes in non-obese people with MAFLD were all signi cantly higher than those in non-obese people without MAFLD (P < 0.001) ( Table 2). Compared with obese people with MAFLD, the proportions of elevated waist circumference, elevated systolic and diastolic pressure and elevated liver enzymes were signi cantly lower in non-obese people with MAFLD, while the proportion of elevated total cholesterol in non-obese people was signi cantly higher.

Discussion
In the present study, the prevalence and risk factors of MAFLD were explored, and the signi cant difference in the prevalence of MAFLD among different groups of gender, age, BMI and female menopausal status were revealed. To our knowledge, this is the rst study focusing on the prevalence and associated metabolic characteristics of MAFLD since the new de nition of MAFLD was set up [4,5].
The prevalence of MAFLD was 26.1% (23.8% after age and sex adjustment), and it was signi cantly higher in males than in females (35.4% vs. 14.1%, and 32.3% vs. 13.4% after age and sex adjustment), which was consistent with previous studies of NAFLD in Asian populations [14]. revealing that male gender is still predominate in MAFLD. The total prevalence reached peak at the age of 55-59 (Fig. 1). In males, the prevalence rises steeply between the age of 18-39, then rose slowly after 40 years and reached peak at the age of 50-54, revealing that MAFLD is more prevalent in men in their middle ages and they were at an increasing risk of having MALFD while in a younger age which need to be paid special attention. We observed that older men had a lower prevalence of MAFLD than middle-aged men, the possible reasons might be as follows: Some people died of other disease in their older age as fatty liver can signi cantly increase overall mortality [15], hence these people cannot be counted in; Compared with old men who usually retire, middle-aged men who are at peak of their careers have much more social engagement like dinner and party to take part in, which might increase their risk of having metabolic disorders. Whereas in females, the prevalence of MAFLD is relatively low before the age of 50, however, it rose sharply between the age of 50-69 and reached peak at the age of 65-69. Notably, the sharply increasing trend in females was consistent with the presence of perimenopausal period, indicating that change of estrogen levels was an important factor of the rapid increase in the prevalence of MAFLD. Besides, after strati cation by menopausal status, the prevalence of MAFLD in females rose steady from premenopausal period (6.1%) to perimenopausal period (16.8%), then to postmenopausal period (30.2%) (Fig. 2). This phenomenon consists with former studies [16], indicating that estrogen might have protective effects against MAFLD in females [17]. Conversely, the decrease of estrogen in perimenopausal and postmenopausal women can lead to fat redistribution and thus causing metabolic disorders including dyslipidemia and glucose intolerance [18], which can also be demonstrated in our study that the prevalence of dyslipidemia (22.9% for premenopausal period, 51.6% for perimenopausal period and 68.8% for postmenopausal period) was parallel with the trend of the MAFLD prevalence strati ed by menopausal status. This nding indicated that the perimenopausal and postmenopausal status might be substantial risk factors for MAFLD in women, suggesting estrogen de ciency in perimenopausal and postmenopausal women may also play an important role in the development of MAFLD.
Previous studies have found that presence of NAFLD is closely related to MS components such as obesity, insulin resistance, hypertension and dyslipidemia, and is considered to be the liver manifestation of MS [19]. Our study has also found that after strati ed by BMI, the prevalence of MAFLD increased sharply with the increase of BMI, reaching 59.8% in obese people (Fig. 3). In binary logistic regression (Table 4), BMI and waist circumference were also signi cantly associated with MAFLD, indicating obesity is closely associated with MAFLD and obesity management should be emphasized as weight loss was proved to reduce steatosis [20].
In people with MAFLD, the proportions of the abnormal metabolic features were all signi cantly higher than those in people without MAFLD (Table 2), con rming that MAFLD is closely associated with MS components including abdominal obesity, hypertension, dyslipidemia, and dysglycemia. Among them, in addition to waist circumference, the most signi cant difference was found in elevated triglyceride, and triglyceride were also shown to be signi cantly associated with MAFLD in logistic regression (Table 4), with the highest OR value of 1.776, suggesting that elevated triglyceride may be an important risk factor of MAFLD. Moreover, the difference in the proportion of elevated fasting glucose was also very signi cant, and fasting glucose was also signi cantly associated with MAFLD in logistic regression with the OR value of 1.403, consisting with the previous study that there's correlation between fatty liver and dyslipidemia and dysglycemia [21]. Studies have also shown that NAFLD is not only closely related to the cardiovascular and renal diseases associated with MS, but also precedes the presentation of metabolic derangements [22], considering the high proportions of abnormal metabolic features (Table 2) and the signi cant high prevalence of MS (53.2% vs. 10.1%) in people with MAFLD ( Fig. 4) in our study, MAFLD may be a signi cant risk factor of MS. Notably, we noticed that the prevalence of MS in females with MAFLD was signi cantly higher than that in males with MAFLD (61.4% vs. 50.6%, P < 0.001) (Fig. 4), indicating that in patients with MAFLD, females may be more susceptible to MS than males. Furthermore, we also found that the prevalence of MAFLD in people without any MS risk factors was 3.3%, while those met all 5 MS criteria had a prevalence of 82.5% (Table 3), and the prevalence of MAFLD in people with MS was signi cantly higher than those without MS (65.1% vs. 15.5%, P < 0.001), which also demonstrated that MS and its components are important risk factors of MAFLD.
It was also shown in our study that the prevalence of dyslipidemia and hyperuricemia was signi cantly higher in people with MAFLD than those without MAFLD (80.0% vs. 41.7% for dyslipidemia and 45.0% vs. 16.8% for hyperuricemia) (Fig. 4). Dyslipidemia is a well-known risk factor for NAFLD [3], and this can also be re ected in the sharp rise of the prevalence of MAFLD in perimenopausal and postmenopausal women in our study, which might be related to the dyslipidemia due to estrogen de ciency (Fig. 2). In binary logistic regression, uric acid was showed to be signi cantly associated with MAFLD. Previous cross-sectional and prospective studies have found that elevated serum uric acid could independently predict the increased risk of NAFLD, even serum uric acid levels within normal range were closely related to the presence of NAFLD independently [23][24][25]. Hence, combining the ndings in our study with previous studies, serum uric acid might be considered as an independent risk factor of MAFLD.
The present study revealed that people with MAFLD are more likely to have elevated liver enzymes especially elevated ALT compared with those without MAFLD (42.5% vs. 11.1% for elevated ALT, P < 0.001) ( Table 2), which stands for the higher proportion of abnormal liver function in people with MAFLD, consisting with the previous study that the most common cause of unexplained elevated ALT is NAFLD [26]. Moreover, Table 4 showed that ALT was signi cantly associated with MAFLD and studies have showed that elevated ALT is associated with the development of NAFLD into steatohepatitis and even liver brosis [27], indicating that elevated ALT has an important clinical signi cance for MAFLD. Platelets are considered to be elevated during in ammation, and studies have found a linear correlation between platelet count and the severity of liver brosis in people with NAFLD [28], in our study, we also found that platelet count was signi cantly associated with MAFLD (Table 4), indicating that platelet count and ALT levels may be used as a reference indicator of MAFLD development and the resulting liver brosis.
Although the occurrence of NAFLD is closely related to obesity, non-obese people may also suffer from NAFLD, especially in the Asia-Paci c region [29]. In our study, the proportions of abnormal metabolic features in non-obese people with MAFLD were all signi cantly higher than those in nonobese people without MAFLD ( Table 2), suggesting that metabolic disorders also play an important role in the occurrence of MAFLD in non-obese people. Notably, the proportion of elevated total cholesterol was signi cantly higher in non-obese people with MAFLD than that in obese people with MAFLD, suggesting total cholesterol may play an important role in the presence of non-obese MAFLD which need to further exploration.
Our study also has certain limitations. First, this is a cross-sectional study, therefore, the natural course of MAFLD and causal relationships can't be determined. There was a large sample size with a wide range of clinical data included in our study, making it possible to adjust for underlying confounding factors. Second, the diagnosis of MAFLD was based on ultrasonography, which might be partially insensitive to mild hepatic steatosis. However, ultrasonography has been widely used in the epidemiological investigations of fatty liver since it is safe, non-invasive, widely available, and has an acceptable sensitivity and speci city in the detection of hepatic steatosis [30], and it was also recommended as the rst-line imaging method by the Association for the Study of the Liver (APASL) in the clinical guideline for MAFLD [31]. Third, there might be certain selection bias because the population who participated in health examination included in our study tend to be more concerned about their health. Furthermore, some information was not available from the current data of health examinations, like medication history of participants.

Conclusions
In conclusion, our study revealed a high prevalence of MAFLD among a general Chinese population, and it varies greatly between different groups of gender, age, BMI and female menopausal status. An increasing prevalence was found to be associated with obesity and multiple metabolic disorders and people with MAFLD suffer a high prevalence of MS, dyslipidemia, and hyperuricemia. The presence of MAFLD and MS interact with each other and they may be the risk factor of each other. Moreover, non-obese people also suffer from MAFLD, and it's also closely related to metabolic disorders. We also con rmed the high proportion of elevated ALT in people with MAFLD. Multiple metabolic disorders especially obesity should be paid great attention to improve the prevention and management of MAFLD. More researches are still needed to determine the potential mechanisms of the occurrence of MAFLD, as well as further relationship and causality between MAFLD and multiple metabolic disorders, which would provide crucial implications for the prevention and treatment of MAFLD.

Declarations
Ethics approval and consent to participate: All procedures in studies involving human participants were performed in accordance with the ethical standards of the institutional research committee (The Ethics Committee of the First A liated Hospital of Chongqing Medical University, approval number: 2019-141) and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The informed consent was waived because the information of all the participants was anonymous.
Consent for publication: Not applicable.
Availability of data and materials: The datasets analysed during the current study are not publicly available because all data were recorded in the electronic medical record system of the Quality Control Center of Health Examination in Chongqing. However, they are available from the corresponding author on reasonable request.
Competing interests: The authors declare that they have no competing interests.
Funding: There is no funding for this research.  Prevalence of MAFLD and dyslipidemia in females divided by menopausal status The prevalence of MAFLD and dyslipidemia and its 95% CIs in females with different menopausal status were calculated.