Pang Q, Zhang JY, Song SD, Qu K, Xu XS, Liu SS, Liu C. Central obesity and nonalcoholic fatty liver disease risk after adjusting for body mass index. World J Gastroenterol 2015; 21(5): 1650-1662 [PMID: 25663786 DOI: 10.3748/wjg.v21.i5.1650]
Corresponding Author of This Article
Chang Liu, MD, PhD, Professor, Department of Hepatobiliary Surgery, the First Affiliated Hospital of Medical College, Xi’an Jiaotong University, No. 277 West Yan-ta Road, Xi’an 710061, Shaanxi Province, China. liuchangdoctor@163.com
Research Domain of This Article
Gastroenterology & Hepatology
Article-Type of This Article
Meta-Analysis
Open-Access Policy of This Article
This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Qing Pang, Jing-Yao Zhang, Si-Dong Song, Kai Qu, Xin-Sen Xu, Su-Shun Liu, Chang Liu, Department of Hepatobiliary Surgery, the First Affiliated Hospital of Medical College, Xi’an Jiaotong University, Xi’an 710061, Shaanxi Province, China
ORCID number: $[AuthorORCIDs]
Author contributions: Pang Q and Zhang JY contributed equally to this work; Pang Q participated in the research design, writing of the paper, and literature searches; Zhang JY participated in writing of the paper, literature searches, and data analysis; Song SD and Qu K participated in critical revision of the paper, and extraction and analysis of data; Xu XS and Liu SS participated in revision of the paper, and final approval; Liu C participated in the research conception and design.
Supported by National Natural Science Foundation of China, No. 30872482 and No. 81072051.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Chang Liu, MD, PhD, Professor, Department of Hepatobiliary Surgery, the First Affiliated Hospital of Medical College, Xi’an Jiaotong University, No. 277 West Yan-ta Road, Xi’an 710061, Shaanxi Province, China. liuchangdoctor@163.com
Telephone: +86-29-82653900 Fax: +86-29-82653905
Received: May 10, 2014 Peer-review started: May 10, 2014 First decision: May 29, 2014 Revised: June 11, 2014 Accepted: August 28, 2014 Article in press: August 28, 2014 Published online: February 7, 2015 Processing time: 275 Days and 16.9 Hours
Abstract
AIM: To investigate whether central obesity is associated with nonalcoholic fatty liver disease (NAFLD) formation after adjusting for general obesity.
METHODS: The online databases PubMed, EMBASE, and ISI Web of Science were searched for studies estimating the influence of central obesity on NAFLD occurrence published through April 2014. Studies that did not adjust for body mass index (BMI) were excluded. In addition, the independent effect of BMI was also assessed with the included studies. The pooled effect sizes and 95% confidence intervals (CIs) were calculated using random- or fixed-effects models based on the degree of heterogeneity. Furthermore, subgroup analyses, meta-regression, sensitivity analyses, and publication bias were performed.
RESULTS: Twenty eligible studies were identified. The summary odds ratio (OR) values per-unit increase in waist circumference (WC) and BMI for NAFLD formation were 1.07 (95%CI: 1.03-1.10, I2 = 73.9%, n = 11 studies) and 1.25 (95%CI: 1.13-1.38, I2 = 88.7%, n = 11 studies), respectively. When the indices were expressed as binary variables (with the non-obesity group as reference), the pooled OR in WC, waist-to-hip ratio, and BMI were 2.34 (95%CI: 1.83-3.00, I2 = 41.8%, n = 7 studies), 4.06 (95%CI: 1.53-10.79, I2 = 65.7%, n = 3 studies), and 2.85 (95%CI: 1.60-5.08, I2 = 57.8%, n = 5 studies), respectively. Using the same studies as the latter (n = 5), pooled OR in WC was 3.14 (95%CI: 2.07-4.77), which is greater than that in BMI.
CONCLUSION: Central obesity may pose a greater threat to national health than general obesity, although both are independently associated with increased risk of NAFLD.
Core tip: Central and general obesity are independently associated with increased risk of nonalcoholic fatty liver disease (NAFLD). Per-unit increase in waist circumference and body mass index increased the incidence risk of NAFLD by 0.07- and 0.25-fold, respectively. The risk for disease is increased in individuals with a higher waist circumference, waist-to-hip ratio, and body mass index by 1.34-, 3.06-, and 1.85-fold, respectively. The results of this analysis suggest that central obesity poses a greater threat to national health than general obesity. Therefore, future studies should place a greater emphasis on central obesity.
Citation: Pang Q, Zhang JY, Song SD, Qu K, Xu XS, Liu SS, Liu C. Central obesity and nonalcoholic fatty liver disease risk after adjusting for body mass index. World J Gastroenterol 2015; 21(5): 1650-1662
Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of non-cancerous liver diseases ranging from simple steatosis to nonalcoholic steatohepatitis (NASH). Considering that NAFLD has been increasingly recognized as a major cause of liver-related mortality, the disease has become a global problem[1,2]. NAFLD may progress to liver fibrosis, liver cirrhosis, or even hepatocellular carcinoma (HCC), the fifth most common cancer and the third most common cause of death from cancer worldwide[3]. Moreover, due to the high prevalence of NAFLD worldwide, especially in developed countries, the incidence of NAFLD-related HCC has gradually increased[4].
As a hepatic manifestation of metabolic syndrome (MS), NAFLD is closely associated with metabolic disorders such as diabetes and obesity[5,6]. The incidences of general/central obesity have greatly increased over the past few decades due to unhealthy dietary patterns, decreased physical activity, and sedentary lifestyles. Along with the rapid increase of obese patients, the morbidity and impact of NAFLD have increased in recent years[6,7]. However, the majority of hepatologists are exclusively focused on the association between general obesity and NAFLD risk, thus neglecting the effect of central obesity. Moreover, several meta-analyses and epidemiological studies demonstrated that central obesity might be a better predictor of metabolic disorders and tumors than general obesity[8-10]. Nevertheless, these studies failed to show the independent risk of central obesity as odds ratio (OR) values were calculated without adjustments for general obesity.
In various definitions of MS[11], central obesity, rather than general obesity, is generally considered to be an indispensable component of MS. This suggests that central obesity should not be neglected as a risk factor for NAFLD. In fact, some individuals with no general obesity could potentially develop NAFLD[12]. Previous studies have demonstrated that patients with NAFLD have significantly higher visceral fat areas and waist circumferences (WCs) compared with body mass indices (BMIs) of matched control individuals[13,14]. In addition, central obesity is an important predictor for NAFLD, even in individuals with normal weight[15,16]. A recent study emphasized that no other anthropomorphic parameters are independently associated with NAFLD after adjusting for waistline[17]. Furthermore, as a metabolic factor, WC is strongly associated with insulin resistance and increased alanine aminotransferase activity in patients with NAFLD[18,19]. According to the above findings, we hypothesized that central obesity is closely associated with the incidence of NAFLD, and the association may be independent of general obesity. However, several epidemiological studies have suggested no statistically significant association between central obesity and NAFLD after adjusting for BMI[20-23]. Thus, the principal aim of this review was to assess whether central obesity independently conveys increased NAFLD risk after excluding BMI as a confounder. All of the relevant studies were summed with the meta-analysis method. Furthermore, the independent effect of BMI in NAFLD was investigated in the included studies.
MATERIALS AND METHODS
Search strategy and selection criteria
Two independent investigators (Pang Q and Zang JY) performed a systematic search with no language restrictions using the PubMed, EMBASE, and ISI Web of Science databases up until April 2014. The core search consisted of terms “central obesity” or “abdominal obesity” or “abdominal adiposity” or “central adiposity” or “waist circumference” or “waist-to-hip ratio” or “waist” or “WC” or “WHR”, combined with terms “nonalcoholic fatty liver” or “nonalcoholic steatohepatitis” or “hepatic steatosis” or “NAFLD” or “NASH”. In addition, the reference lists of included studies and review articles were searched by hand.
Included studies had to meet the following criteria: (1) published as an original article; (2) used a cohort, case-control, cross-sectional, or nested case-control design; (3) estimated the association between WC or waist-to-hip ratio (WHR) and the incidence of NAFLD in adults, and reported OR value with 95% confidence interval (CI) adjusting for BMI; and (4) diagnosed NAFLD by imaging or biopsy, and excluded patients with alcoholic liver disease (ALD). If a study was published more than once, the publication with the most adjusted OR value was used. Studies were excluded if they recruited all fatty liver patients without distinguishing NAFLD from ALD. A study was excluded if it met one of the following criteria: (1) evaluated the influence of WC in the progress of NAFLD; (2) recruited non-adult individuals; (3) recruited special individuals with pre-existing diseases (diabetes, obese); (4) not published as full reports (conference abstracts and letters to editors); and (5) reported only the relation between central obesity and NAFLD-related fibrosis, cirrhosis, or cancer.
Data extraction
Three investigators (Pang Q, Qu K, Xu XS) independently evaluated and retrieved studies for inclusion according to the selection criteria. Discrepancies among investigators were solved through discussion. For each included study, the following information was extracted using a standardized protocol for collecting data: (1) the first author’s last name; (2) publication year; (3) region in which the study population dwelled; (4) number of recruited patients; (5) cohort characteristics (age, sex, and WC); (6) study design; (7) diagnostic basis for NAFLD; (8) the cut-off values for WC, WHR, and BMI (if reported); (9) OR value and 95%CI; and (10) controlled confounders. The MOOSE guidelines[24] were followed for the current meta-analysis, and the quality of each study was assessed using the Newcastle-Ottawa Scale. All data were double-checked by a single investigator (PQ).
Statistical methods
WC/WHR ratio was expressed as a binary variable in most of the included studies. This did not meet the specific requirement in at least three categories of dose-response meta-analysis[25,26]. In other words, binary variables (with a lower level as a reference) could not be converted to continuous variables (expressed OR value as a slope per-unit increase in variables) by using generalized least-squares trend estimation. Thus, the two types of variables were analyzed separately to estimate the association between central obesity and the risk of NAFLD occurrence. Variables that entered multiple factor analyses in the corresponding study were considered as adjusted confounders.
The heterogeneity among studies was assessed with Q and I2 statistic values (25%, 50%, and 75% correspond to cut-off points for low, moderate, and high degrees of heterogeneity, respectively). A fixed-effects model was used when significant heterogeneity was observed [P < 0.1 (Q), or I2 > 50%]; otherwise, a random-effects model was used. To identify those factors that could significantly alter the pooled OR value, as well as to explore the source of heterogeneity among studies, subgroup and meta-regression analyses were performed for the covariates in at least two studies in each group. Sensitivity analyses were performed to investigate whether any single study markedly affected the results, and the effects model was used to observe changes in the results. Publication bias was examined in funnel plots using Begg’s and Egger’s tests. The STATA software, version 12.0 (StataCorp LP, College Station, TX, United States) was used to analyze the data.
RESULTS
Identification and selection of studies
A flow diagram of the literature search and selection process is shown in Figure 1. Of the total 1664 citations, 21 datasets were identified in 20 studies (published 2005-2013)[20-23,27-42]. The consensus among the three observers concerning which studies to include was good (κ = 0.925-0.974). No additional articles were included from review of the references. Thus, a total of 21 datasets were used in this meta-analysis; 11 of which expressed OR values as a slope per-unit increase in WC. Seven studies reported OR values for WC, and three studies reported ORs for WHR with the lower category (a subgroup with a lower level) as a reference. One cohort study estimated the association between WC and NAFLD without distinguishing the NAFLD incidence rate (185 patients) from the NAFLD prognosis (26 patients)[40]. The qualities of the studies were moderate to high (mean Newcastle-Ottawa Scale score 7.24, range: 6-9). With exception of two Korean studies, all articles were published in English.
Figure 1 Flow diagram of search strategy and study selection.
ALD: Alcoholic liver disease; OR: Odds ratio; WC: Waist circumference; WHR: Waist-to-hip ratio.
Characteristics of included studies
The baselines of the included studies are summarized in Table 1. The meta-analysis involved 12065 cases (9135 men and 2930 women) and 33692 controls (15983 men and 15709 women). Two studies used a prospective cohort design; five studies used case-control or nested case-control designs, whereas the remaining studies used a cross-sectional design. All studies recruited both men and women except one study that exclusively recruited men[22]. Three studies were performed in western countries (Europe and the United States), and others were from Asia. The mean patient age ranged from 35.5 to 71.9 years. NAFLD was assessed by imaging (computed tomography or ultrasound) in all the included studies.
Table 1 Baseline characteristics for studies included in meta-analysis.
Figure 2A-C shows the results of meta-analyses for WC and WHR. Eleven studies involving 10 454 individuals estimated OR values as a slope unit increase in WC. A high degree of heterogeneity was observed (I2 = 73.9%; P = 0.000), and thus, the summary OR value was calculated using a random-effects model. WC was independently associated with NAFLD, and the pooled OR value was 1.065 (95%CI: 1.029-1.103). When stratified by region, the OR values were 1.076 and 1.031 in the Asian (nine studies) and American (two studies) populations, respectively.
Figure 2 Meta-analyses of the included studies.
Forest plots of studies for the associations of various obesity parameters with nonalcoholic fatty liver disease generated using random-effects model analyses (exception: fixed-effects model for plot in B). A: Per-unit increase in waist circumference (WC); B: High vs low category of WC; C: High vs low category of WHR; D: Per-unit increase in BMI; E: High vs low category of BMI.
A meta-analysis was performed from six cross-sectional, and one nested case-control studies that expressed WC as a binary variable. WC cut-off values were all in accordance with the definition of central obesity of the national or international scientific associations/federations. A fixed-effects model was used when a low heterogeneity was present (I2 = 41.8%; P = 0.112). The pooled effect size was 2.344 (95%CI: 1.831-3.0), and the result suggested that central obesity was independently associated with NAFLD.
WHR is another accepted anthropometric measure for defining central obesity. Three studies estimated the influence of elevated WHR level in the occurrence of NAFLD. The summary OR value was 4.061 (95%CI: 1.529-10.790), with moderate heterogeneity among studies (I2 = 65.7%; P = 0.054).
Pooled OR value for BMI
To utilize the included studies fully, the association between BMI and NAFLD risk was estimated after adjusting for WC. The results summarizing 16 studies are shown in Figure 2D and E. A per-unit increase in BMI was independently associated with the risk of NAFLD, with significant heterogeneity among studies (OR = 1.250, 95%CI: 1.131-1.382, I2 = 88.7%; P = 0.000). Stratified by region, the pooled OR values in the eastern (Asia) and western (Europe and the US) populations were 1.307 and 1.023, respectively. There was no significant heterogeneity among the studies performed in western regions (I2 = 0.0%; P = 0.331).
Five Asian studies expressed BMI as a binary variable. Four of them evaluated NAFLD risk in overweight individuals (in comparison to the lower BMI level), and one estimated risk in obese patients. Given moderate heterogeneity among studies (I2 = 57.8%; P = 0.050), a random-effects model was implemented indicating an overall adjusted OR of 2.854 (95%CI: 1.604-5.080).
Exploration of heterogeneity
With 11 studies estimating the influence of per-unit WC increase in NAFLD, subgroup and meta-regression analyses were performed for the covariates region, design method, number of adjusted confounders, and the number of involved patients. The covariate regions and number of individuals were analyzed for seven studies estimating the association between central obesity and NAFLD (Table 2). When WC was expressed as a continuous variable, the number of individuals and adjusted confounders affected the summary effect size. The OR value was found to be statistically significant (lower CI > 1) only in studies with > 700 individuals, and more than three adjusted confounders. There were significantly higher heterogeneities and wider CIs in the subgroups of: eastern population, cross-sectional study, fewer adjusted potential confounders, and fewer individuals. For all the covariates, no significant between-group differences were found in univariate or multivariate meta-regression analyses.
Table 2 Subgroup and meta-regression analyses of waist circumference and the risk of nonalcoholic fatty liver disease.
Covariates
Subgroup
Studies, n
OR(95%CI)
P of Q
I2
Inter-groupP value
UnivariateP value
MultivariateP value
Per-unit increase in waist circumference
Region
East
9
1.076 (1.025-1.129)
0.000
73.6
0.006
0.171
0.214
West
2
1.031 (1.016-1.046)
0.535
0.0
Design
c-s
8
1.063 (1.014-1.114)
0.000
79.1
0.157
0.764
0.984
Others
3
1.071 (1.026-1.119)
0.254
26.9
Adjusted
Yes
7
1.051 (1.019-1.084)
0.035
55.8
0.031
0.489
0.770
(> 3 confounders)
No
4
1.126 (1.000-1.269)
0.000
85.0
Individuals
Yes
6
1.054 (1.025-1.083)
0.055
56.7
0.163
0.728
0.975
(> 700)
No
5
1.100 (0.991-1.22)
0.000
81.5
High vs low category of waist circumference
Design
c-s
5
2.113 (1.615-2.765)
0.180
36.2
0.057
0.642
0.947
Others
2
4.072 (2.189-7.575)
0.512
0.0
Individuals
Yes
3
2.070 (1.546-2.774)
0.245
28.9
0.122
0.635
0.942
(> 600)
No
4
3.185 (2.010-5.046)
0.164
41.2
Further analysis with several additional studies
Nine additional studies were identified for further exploration. Although all the studies provided OR values that estimated the influence of per-unit WC in NAFLD incidence, six studies calculated ORs without adjusting for BMI[17,43-47] and four studies recruited patients without excluding ALD[47-50] (Table 3). Likewise, when stratified by geographic region, the association was stronger in the eastern populations (OR = 1.089, I2 = 94.1%; P = 0.000) in comparison with the western populations (OR = 1.040, I2 = 40.8%; P = 0.149). Moreover, the association between WC and risk of NAFLD was stronger in case-control/cohort studies than in cross-sectional studies (P = 0.010). There were higher heterogeneities and wider CIs in the subgroups of an eastern population, cross-sectional study, without adjusting for BMI, and without excluding ALD; all of which could be a source of heterogeneity (P < 0.05). For all the covariates, no significant between-group differences were found by univariate and multivariate meta-regression analyses.
Table 3 Further analyses after adding several studies.
Covariates
Subgroup
n of studies
OR(95%CI)
P of Q
I2
Inter-studyP value
UnivariateP value
MultivariateP value
Per-unit increase in waist circumference
Region
East
15
1.089 (1.057-1.122)
0.000
94.1
0.001
0.180
0.145
West
5
1.040 (1.028-1.052)
0.149
40.8
Design
c-s
14
1.067 (1.042-1.193)
0.000
94.6
0.010
0.734
0.968
Others
6
1.076 (1.049-1.103)
0.140
39.8
Adjusted
Yes
11
1.059 (1.038-1.081)
0.000
82.9
0.806
0.393
/
(> 3 factors)
No
9
1.101 (1.055-1149)
0.000
95.9
Adjusting for BMI
Yes
14
1.064 (1.040-1.089)
0.000
84.8
0.000
0.649
0.918
No
6
1.086 (1.046-1.127)
0.000
95.3
Excluding ALD
Yes
16
1.079 (1.051-1.107)
0.000
90.0
0.000
0.603
0.869
No
4
1.056 (1.022-1.093)
0.000
93.8
High vs low category of waist circumference
Region
East
11
2.687 (2.018-3.579)
0.000
74.4
0.000
0.545
0.934
West
5
3.098 (2.005-4.785)
0.000
83.3
Design
c-s
12
2.471 (1.958-3.119)
0.000
72.3
0.000
0.015
0.078
Other
4
5.212 (2.121-12.807)
0.858
0.0
Adjusted
Yes
10
3.002 (2.268-3.973)
0.000
73.1
0.000
0.459
/
(> 3 factors)
No
6
2.840 (2.184-3.691)
0.000
75.2
Adjusting for BMI
Yes
10
2.492 (1.898-3.271)
0.002
65.8
0.000
0.221
0.591
No
6
3.281 (2.308-4.664)
0.000
79.5
Excluding ALD
Yes
12
2.856 (2.115-3.855)
0.000
74.9
0.000
0.910
1.000
No
4
2.794 (1.716-4.549)
0.000
89.5
Similarly, further analysis was performed after the addition of nine studies estimating NAFLD risk in individuals with central obesity. Of these nine studies, five OR values were not adjusted for BMI[22,51-54], and four studies did not distinguish ALD from NAFLD[55-58]. The result was inconsistent with the previous results after being stratified by region, as the OR value in the western population (3.098) was higher than in the eastern population (2.687). Univariate meta-regression analyses demonstrated that the association was significantly stronger in studies with a case-control or cohort design than in cross-sectional studies (P = 0.015). However, the statistical significance disappeared in multivariable meta-regression (P = 0.078). There were no significant between-group differences for other covariates in univariate and multivariate meta-regression analyses.
Sensitivity analysis and test of publication bias
To compare the degree of influence of central and general obesity in the NAFLD incidence rate, the five studies that provided adjusted OR estimations of both higher vs lower WC and higher vs lower BMI, were analyzed separately. The results showed a greater risk of NAFLD in individuals with central obesity in comparison with individuals with higher BMI levels. All the results were consistent, with no significant differences between fixed-effects or random-effects models were found (Table 4). WHR, which had the greatest effect in both effects models, might be the best parameter in predicting NAFLD. In addition, the influence analyses found that no single study affected the summary estimates (not shown).
Table 4 Summary estimates by fixed- vs random-effects methods.
There was no statistical evidence of publication bias among studies expressing WC as a continuous variable (P = 0.436 using Begg’s test; P = 0.222 using Egger’s test), as well as among studies expressing WC as a binary variable (P = 0.230 using Begg’s test; P = 0.092 using Egger’s test) (Figure 3).
Figure 3 Funnel plots for publication bias.
A: Per-unit increase in waist circumference (WC) (P = 0.436); B: High vs low category of WC (P = 0.230); C: Per-unit increase in body mass index (BMI) (P = 0.533); D: High vs low category of BMI (P = 0.086). s.e.: Standard error.
DISCUSSION
This is believed to be the first meta-analysis investigating the independent relationship between two types of obesity and NAFLD risk. The results indicate that high WC, WHR and BMI levels are all independently associated with NAFLD. WC and BMI per-unit increases led to 0.07- and 0.25-fold increases in the risk of developing NAFLD, respectively. Individuals with higher levels of WC, WHR or BMI (with a lower level as a reference) faced an increase in the NAFLD incidence rate by 1.34-, 3.06- and 1.85-fold, respectively. When these factors are expressed as continuous variables, comparing the strength of association among the three anthropomorphic parameters is meaningless due to enormous differences in their values and ranges. In contrast, it is more meaningful to compare the strength between higher WC (or WHR) level and higher BMI level within the same studies. This approach showed that patients with central obesity had a higher risk of NAFLD than individuals with general obesity.
This study demonstrates a stronger association between obesity and NAFLD risk in the eastern population compared with the western population when WC and BMI were reported as measurement data. Therefore, region may have been a potential source of heterogeneity in these studies. However, when WC was expressed as a categorical variable, individuals in the west had a greater NAFLD risk. This contradiction is easily explained by the fact that the WC cut-off-value was higher in westerners (102 cm) than easterners (90 cm). Further analysis with 18 additional datasets found that the region, design, adjusting for BMI, and excluding ALD were all potential causes of heterogeneity. However, none of the covariates were statistically different by multivariate meta-regression. The lack of significant changes after excluding any single study or using the other effects model demonstrates the reliability of the results from this meta-analysis.
Obesity has been shown to be an important risk factor for many liver diseases[59]. Most hepatologists stress only the role of general obesity on the etiologies of these disorders while ignoring the special role of central obesity. Central obesity can also lead to some hepatic pathological changes. It is still not clear whether the effect of central obesity on NAFLD is independent of general obesity. Our findings have clarified this controversy, and can easily explain why some patients with NAFLD have a normal BMI level but an expanded waistline. We also verified that the impact of central obesity was more serious than the impact of general obesity. Furthermore, the independent effects of the two obesity modes suggested that they might be synergistic risk factors for NAFLD. This supposition is consistent with an Asian study that indicated that patients with both general and central obesity showed more than twofold risk of developing fatty liver compared to obese individuals with no central obesity[16]. General obesity is mainly caused by overeating, whereas central obesity is a result of a sedentary lifestyle. Thus, our results emphasize the importance of considering the pathophysiological factor when treating NAFLD. The individuals with an elevated BMI, as well as a wider waistline, should follow moderate diets and increase physical activity as a preventive measure against NAFLD. While only few studies reported an association between central obesity and HCC, several meta-analyses have demonstrated a significant increase in cancer risk in patients with central obesity[10,60,61]. The significant effects of WC and WHR on NAFLD, a pivotal cause of HCC, may partly suggest that central obesity could independently increase HCC risk.
Some investigations have previously reported an association between increased abdominal obesity and hepatic steatosis. There were some shortcomings in these studies. On one hand, many of the studies assessed NAFLD by abnormal liver biochemistry levels[62,63]. Although most patients with this disorder demonstrate abnormal liver function, Sorrentino et al[64] indicated that liver enzyme levels could not be used as surrogate markers of NAFLD. On the other hand, some of the studies involved all fatty liver patients, but failed to distinguish NAFLD from ALD. Despite NAFLD and ALD having similar pathology performance and pathogenesis, the nutritional status and adiposity condition of the two diseases are different. Central obesity is not a significant determinant for ALD-induced liver dysfunction[65,66]. Moreover, there is a synergistic effect between risky alcohol consumption and obesity in relation to liver diseases[67]. Thus, to improve the accuracy of diagnosis and reduce heterogeneity among studies, only studies that assessed NAFLD by imaging/biopsy were included and those involving ALD were excluded. The influence of ALD on heterogeneity was tested in our further analyses. In addition, as the diagnostic criteria for children’s central obesity are significantly different from those for adults, we excluded studies that did not recruit adults. To assess the validity and reliability of our results, subgroup analyses, meta-regression, and sensitivity analyses were performed.
The rigorous selection criteria of our study may have led to some potential limitations. First, NAFLD is highly prevalent in obese children[68], and our restriction to adults meant that we were unable to extrapolate the risk of obesity to children. Second, liver biopsy is universally considered the best tool for identifying NAFLD. However, none of our included studies diagnosed fatty liver by biopsy. Third, the effect of obesity may be different between men and women. Previous studies suggested that the hypoandrogenism in men and hyperandrogenism in women can potentially lead to NAFLD via obesity[69]. In addition, there is a correlation between liver fat deposition and WC in men with NAFLD, but not in women[70]. Thus, our results may produce gender distinction, and gender may be a potential source of heterogeneity. Few studies separately reported OR values for both genders, thus, we could not stratify by gender. Finally, the causal exploration designs, such as cohort, case-control, and cross-sectional design, have lower reliability[71]. Involving more cohort design studies would strengthen the argument, something that our study did not do.
There are a variety of reasons why central obesity induces fatty liver. Central obesity is an essential component of MS; a disorder strongly associated with many metabolic factors. As an indispensable metabolic organ, the liver is inseparable from metabolism. These universally accepted facts disclose the intrinsic links between central obesity and liver diseases. Additionally, NAFLD is often accompanied by diabetes, dyslipidemia, and hypertension[72,73], and these metabolic disorders could coexist in non-general obese individuals[74]. A case-control study showed that central obesity without insulin resistance can play a limited role in fatty liver[75], indicating that metabolic factors were significant in the role of central obesity. These results suggest that central obesity-induced metabolic disorders may be a major cause for NAFLD. Furthermore, central obesity could disturb the secretion of adipose tissue-derived adipokines, subsequently leading to an increase in harmful (tumor necrosis factor-α, interleukin-6, and resistin) and a decrease in protective (adiponectin) adipocytokines[76,77]. Increased serum levels of detrimental cytokines in obese subjects accelerate the occurrence of NAFLD[78,79].
As no therapies have been widely accepted, the treatment of NAFLD is another puzzling problem. Dietary modification (total calorie, fat, and carbohydrate restriction), exercise, weight loss, pharmacotherapy, and surgical intervention are potential options[80-82]. It is worth noting that bariatric surgery could improve hepatic histology in most of the obese NAFLD patients, however, a small number of patients, especially those who lose weight too rapidly, might become worse[83]. There are some animal data, as well as preliminary human data, showing that metformin may offer some benefits for NAFLD[84]. Liver transplantation is still the best choice for patients with decompensated nonalcoholic cirrhosis[85].
NAFLD is considered as a cause of many other liver diseases. Thus, our results suggest that central obesity poses a bigger threat to national health than general obesity. However, further investigation is still needed to determine whether central obesity is independently associated with NAFLD-related disorders, and whether it can induce NAFLD that progresses into NASH, cirrhosis, or HCC.
ACKNOWLEDGMENTS
The authors gratefully acknowledge Ming-Hui Tai from the University of Kansas for polishing the manuscript.
COMMENTS
Background
Nonalcoholic fatty liver disease (NAFLD) can progress to liver fibrosis, liver cirrhosis, or hepatocellular carcinoma (HCC). HCC is the fifth most common cancer and the third most common cause of death from cancer worldwide. Due to the high prevalence of NAFLD worldwide, especially in developed countries, the incidence of HCC in NAFLD has increased. Moreover, there has been an increase in the obesity rate and the morbidity and impact of NAFLD.
Research frontiers
The majority of hepatologists focus exclusively on the association between general obesity and NAFLD risk, while neglecting the influence of central obesity. Several meta-analyses and epidemiological studies have indicated that central obesity is a better predictor of metabolic disorders and tumors than general obesity. Nevertheless, these studies failed to show an independent risk of central obesity as they reported odds ratio values without adjusting for general obesity.
Innovations and breakthroughs
This is the first meta-analysis to investigate the independent relationship between general/central obesity and NAFLD risk. A total of 12065 cases and 33692 controls in 20 studies were included. The results indicate that higher waist circumference (WC), waist-to-hip ratio (WHR), and body mass index (BMI) are all independently associated with NAFLD. Therefore, patients with central obesity are at a higher risk of developing NAFLD than individuals with general obesity.
Applications
General obesity is caused mainly by overeating while central obesity results from a sedentary lifestyle. Thus, our results emphasize the importance of considering the pathophysiological factor in the treatment of NAFLD. Individuals with an elevated BMI and a wider waistline should follow moderate diets and increase exercise levels to prevent NAFLD. The significant effects of WC and WHR on NAFLD, a pivotal cause of HCC, suggest that central obesity could independently increase HCC risk.
Terminology
WC, a common anthropometric measure for defining central obesity, is related to many diseases, especially metabolic diseases. WHR is another index for defining central obesity. Abnormal BMIs, the most important index for defining general obesity, could increase the morbidity and mortality rates of many diseases, as well as a variety of tumors.
Peer-review
This meta-analysis is the result of an extensive and rigorous selection of articles. The statistical analysis is comprehensive and rigorously presented. The discussions are logical. The authors observed that both central and general obesity, particularly increases in WC and BMI, are independently associated with increased risk of NAFLD.
Footnotes
P- Reviewer: Carulli L, Eshraghian A, Mihaila RG S- Editor: Ma YJ L- Editor: Kerr C E- Editor: Liu XM
Lv WS, Sun RX, Gao YY, Wen JP, Pan RF, Li L, Wang J, Xian YX, Cao CX, Zheng M. Nonalcoholic fatty liver disease and microvascular complications in type 2 diabetes.World J Gastroenterol. 2013;19:3134-3142.
[PubMed] [DOI][Cited in This Article: ]
Vernon G, Baranova A, Younossi ZM. Systematic review: the epidemiology and natural history of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis in adults.Aliment Pharmacol Ther. 2011;34:274-285.
[PubMed] [DOI][Cited in This Article: ]
Yasutake K, Kohjima M, Kotoh K, Nakashima M, Nakamuta M, Enjoji M. Dietary habits and behaviors associated with nonalcoholic fatty liver disease.World J Gastroenterol. 2014;20:1756-1767.
[PubMed] [DOI][Cited in This Article: ]
Ma Y, Yang Y, Wang F, Zhang P, Shi C, Zou Y, Qin H. Obesity and risk of colorectal cancer: a systematic review of prospective studies.PLoS One. 2013;8:e53916.
[PubMed] [DOI][Cited in This Article: ]
Frank LK, Heraclides A, Danquah I, Bedu-Addo G, Mockenhaupt FP, Schulze MB. Measures of general and central obesity and risk of type 2 diabetes in a Ghanaian population.Trop Med Int Health. 2013;18:141-151.
[PubMed] [DOI][Cited in This Article: ]
Harvie M, Hooper L, Howell AH. Central obesity and breast cancer risk: a systematic review.Obes Rev. 2003;4:157-173.
[PubMed] [DOI][Cited in This Article: ]
Bruce KD, Byrne CD. The metabolic syndrome: common origins of a multifactorial disorder.Postgrad Med J. 2009;85:614-621.
[PubMed] [DOI][Cited in This Article: ]
Liu CJ. Prevalence and risk factors for non-alcoholic fatty liver disease in Asian people who are not obese.J Gastroenterol Hepatol. 2012;27:1555-1560.
[PubMed] [DOI][Cited in This Article: ]
Targher G, Bertolini L, Rodella S, Zoppini G, Zenari L, Falezza G. Associations between liver histology and cortisol secretion in subjects with nonalcoholic fatty liver disease.Clin Endocrinol (Oxf). 2006;64:337-341.
[PubMed] [DOI][Cited in This Article: ]
Chalasani N, Crabb DW, Cummings OW, Kwo PY, Asghar A, Pandya PK, Considine RV. Does leptin play a role in the pathogenesis of human nonalcoholic steatohepatitis?Am J Gastroenterol. 2003;98:2771-2776.
[PubMed] [DOI][Cited in This Article: ]
Fan JG, Saibara T, Chitturi S, Kim BI, Sung JJ, Chutaputti A. What are the risk factors and settings for non-alcoholic fatty liver disease in Asia-Pacific?J Gastroenterol Hepatol. 2007;22:794-800.
[PubMed] [DOI][Cited in This Article: ]
Otgonsuren M, Stepanova M, Gerber L, Younossi ZM. Anthropometric and clinical factors associated with mortality in subjects with nonalcoholic fatty liver disease.Dig Dis Sci. 2013;58:1132-1140.
[PubMed] [DOI][Cited in This Article: ]
Fraser A, Longnecker MP, Lawlor DA. Prevalence of elevated alanine aminotransferase among US adolescents and associated factors: NHANES 1999-2004.Gastroenterology. 2007;133:1814-1820.
[PubMed] [DOI][Cited in This Article: ]
Seo JA, Kim NH, Park SY, Kim HY, Ryu OH, Lee KW, Lee J, Kim DL, Choi KM, Baik SH. Serum retinol-binding protein 4 levels are elevated in non-alcoholic fatty liver disease.Clin Endocrinol (Oxf). 2008;68:555-560.
[PubMed] [DOI][Cited in This Article: ]
Eshraghian A, Dabbaghmanesh MH, Eshraghian H, Fattahi MR, Omrani GR. Nonalcoholic fatty liver disease in a cluster of Iranian population: thyroid status and metabolic risk factors.Arch Iran Med. 2013;16:584-589.
[PubMed] [DOI][Cited in This Article: ]
Church TS, Kuk JL, Ross R, Priest EL, Biltoft E, Blair SN. Association of cardiorespiratory fitness, body mass index, and waist circumference to nonalcoholic fatty liver disease.Gastroenterology. 2006;130:2023-2030.
[PubMed] [DOI][Cited in This Article: ]
Li H, Dong K, Fang Q, Hou X, Zhou M, Bao Y, Xiang K, Xu A, Jia W. High serum level of fibroblast growth factor 21 is an independent predictor of non-alcoholic fatty liver disease: a 3-year prospective study in China.J Hepatol. 2013;58:557-563.
[PubMed] [DOI][Cited in This Article: ]
Stroup DF, Berlin JA, Morton SC, Olkin I, Williamson GD, Rennie D, Moher D, Becker BJ, Sipe TA, Thacker SB. Meta-analysis of observational studies in epidemiology: a proposal for reporting. Meta-analysis Of Observational Studies in Epidemiology (MOOSE) group.JAMA. 2000;283:2008-2012.
[PubMed] [DOI][Cited in This Article: ]
Greenland S, Longnecker MP. Methods for trend estimation from summarized dose-response data, with applications to meta-analysis.Am J Epidemiol. 1992;135:1301-1309.
[PubMed] [DOI][Cited in This Article: ]
Renehan AG, Tyson M, Egger M, Heller RF, Zwahlen M. Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies.Lancet. 2008;371:569-578.
[PubMed] [DOI][Cited in This Article: ]
Zelber-Sagi S, Nitzan-Kaluski D, Halpern Z, Oren R. Prevalence of primary non-alcoholic fatty liver disease in a population-based study and its association with biochemical and anthropometric measures.Liver Int. 2006;26:856-863.
[PubMed] [DOI][Cited in This Article: ]
Park SK, Lee HJ, Lee DH, Lee SK, Chun BY, Kim SA, Lee HS, Son HK, Kim SH. [Associations of non alcoholic fatty liver with the metabolic syndrome and serum carotenoids].J Prev Med Public Health. 2008;41:39-44.
[PubMed] [DOI][Cited in This Article: ]
Choi SY, Kim D, Kang JH, Park MJ, Kim YS, Lim SH, Kim CH, Lee HS. [Nonalcoholic fatty liver disease as a risk factor of cardiovascular disease: relation of non-alcoholic fatty liver disease to carotid atherosclerosis].Korean J Hepatol. 2008;14:77-88.
[PubMed] [DOI][Cited in This Article: ]
Tsai CH, Li TC, Lin CC. Metabolic syndrome as a risk factor for nonalcoholic fatty liver disease.South Med J. 2008;101:900-905.
[PubMed] [DOI][Cited in This Article: ]
Kogiso T, Moriyoshi Y, Shimizu S, Nagahara H, Shiratori K. High-sensitivity C-reactive protein as a serum predictor of nonalcoholic fatty liver disease based on the Akaike Information Criterion scoring system in the general Japanese population.J Gastroenterol. 2009;44:313-321.
[PubMed] [DOI][Cited in This Article: ]
Das K, Das K, Mukherjee PS, Ghosh A, Ghosh S, Mridha AR, Dhibar T, Bhattacharya B, Bhattacharya D, Manna B. Nonobese population in a developing country has a high prevalence of nonalcoholic fatty liver and significant liver disease.Hepatology. 2010;51:1593-1602.
[PubMed] [DOI][Cited in This Article: ]
Pinidiyapathirage MJ, Dassanayake AS, Rajindrajith S, Kalubowila U, Kato N, Wickremasinghe AR, de Silva HJ. Non-alcoholic fatty liver disease in a rural, physically active, low income population in Sri Lanka.BMC Res Notes. 2011;4:513.
[PubMed] [DOI][Cited in This Article: ]
Zheng RD, Chen ZR, Chen JN, Lu YH, Chen J. Role of Body Mass Index, Waist-to-Height and Waist-to-Hip Ratio in Prediction of Nonalcoholic Fatty Liver Disease.Gastroenterol Res Pract. 2012;2012:362147.
[PubMed] [DOI][Cited in This Article: ]
Wengert S, Oeztuerk S, Haenle MM, Koenig W, Imhof A, Boehm BO, Wilhelm M, Mao R, Mason RA, Kratzer W. Association of proinsulin and hepatic steatosis in a random, population-based sample.Eur J Endocrinol. 2013;168:195-202.
[PubMed] [DOI][Cited in This Article: ]
Yoon D, Lee SH, Park HS, Lee JH, Park JS, Cho KH, Kim SM. Hypoadiponectinemia and insulin resistance are associated with nonalcoholic fatty liver disease.J Korean Med Sci. 2005;20:421-426.
[PubMed] [DOI][Cited in This Article: ]
Sung KC, Ryan MC, Kim BS, Cho YK, Kim BI, Reaven GM. Relationships between estimates of adiposity, insulin resistance, and nonalcoholic fatty liver disease in a large group of nondiabetic Korean adults.Diabetes Care. 2007;30:2113-2118.
[PubMed] [DOI][Cited in This Article: ]
Xu C, Xu L, Yu C, Miao M, Li Y. Association between thyroid function and nonalcoholic fatty liver disease in euthyroid elderly Chinese.Clin Endocrinol (Oxf). 2011;75:240-246.
[PubMed] [DOI][Cited in This Article: ]
Sathiaraj E, Chutke M, Reddy MY, Pratap N, Rao PN, Reddy DN, Raghunath M. A case-control study on nutritional risk factors in non-alcoholic fatty liver disease in Indian population.Eur J Clin Nutr. 2011;65:533-537.
[PubMed] [DOI][Cited in This Article: ]
Zhou YJ, Li YY, Nie YQ, Huang CM, Cao CY. Natural course of nonalcoholic fatty liver disease in southern China: a prospective cohort study.J Dig Dis. 2012;13:153-160.
[PubMed] [DOI][Cited in This Article: ]
Cheah WL, Lee PY, Chang CT, Mohamed HJ, Wong SL. Prevalence of ultrasound diagnosed nonalcoholic fatty liver disease among rural indigenous community of Sarawak and its association with biochemical and anthropometric measures.Southeast Asian J Trop Med Public Health. 2013;44:309-317.
[PubMed] [DOI][Cited in This Article: ]
Foster T, Anania FA, Li D, Katz R, Budoff M. The prevalence and clinical correlates of nonalcoholic fatty liver disease (NAFLD) in African Americans: the multiethnic study of atherosclerosis (MESA).Dig Dis Sci. 2013;58:2392-2398.
[PubMed] [DOI][Cited in This Article: ]
Ying X, Jiang Y, Qian Y, Jiang Z, Song Z, Zhao C. Association between Insulin Resistance, Metabolic Syndrome and Nonalcoholic Fatty Liver Disease in Chinese Adults.Iran J Public Health. 2012;41:45-49.
[PubMed] [DOI][Cited in This Article: ]
Hu X, Huang Y, Bao Z, Wang Y, Shi D, Liu F, Gao Z, Yu X. Prevalence and factors associated with nonalcoholic fatty liver disease in Shanghai work-units.BMC Gastroenterol. 2012;12:123.
[PubMed] [DOI][Cited in This Article: ]
Sung KC, Kim BS, Cho YK, Park DI, Woo S, Kim S, Wild SH, Byrne CD. Predicting incident fatty liver using simple cardio-metabolic risk factors at baseline.BMC Gastroenterol. 2012;12:84.
[PubMed] [DOI][Cited in This Article: ]
Yoo HJ, Park MS, Lee CH, Yang SJ, Kim TN, Lim KI, Kang HJ, Song W, Yeon JE, Baik SH. Cutoff points of abdominal obesity indices in screening for non-alcoholic fatty liver disease in Asians.Liver Int. 2010;30:1189-1196.
[PubMed] [DOI][Cited in This Article: ]
Kim C, Harlow SD, Karvonen-Gutierrez CA, Randolph JF, Helmuth M, Kong S, Nan B, Carlos R. Racial/ethnic differences in hepatic steatosis in a population-based cohort of post-menopausal women: the Michigan Study of Women’s Health Across the Nation.Diabet Med. 2013;30:1433-1441.
[PubMed] [DOI][Cited in This Article: ]
Bedogni G, Bellentani S, Miglioli L, Masutti F, Passalacqua M, Castiglione A, Tiribelli C. The Fatty Liver Index: a simple and accurate predictor of hepatic steatosis in the general population.BMC Gastroenterol. 2006;6:33.
[PubMed] [DOI][Cited in This Article: ]
Fan JG, Zhu J, Li XJ, Chen L, Li L, Dai F, Li F, Chen SY. Prevalence of and risk factors for fatty liver in a general population of Shanghai, China.J Hepatol. 2005;43:508-514.
[PubMed] [DOI][Cited in This Article: ]
Cheng YL, Wang YJ, Kao WY, Chen PH, Huo TI, Huang YH, Lan KH, Su CW, Chan WL, Lin HC. Inverse association between hepatitis B virus infection and fatty liver disease: a large-scale study in populations seeking for check-up.PLoS One. 2013;8:e72049.
[PubMed] [DOI][Cited in This Article: ]
Liu SH, Lazo M, Koteish A, Kao WH, Shih MH, Bonekamp S, Hernaez R, Clark JM. Oral contraceptive pill use is associated with reduced odds of nonalcoholic fatty liver disease in menstruating women: results from NHANES III.J Gastroenterol. 2013;48:1151-1159.
[PubMed] [DOI][Cited in This Article: ]
Koehler EM, Schouten JN, Hansen BE, van Rooij FJ, Hofman A, Stricker BH, Janssen HL. Prevalence and risk factors of non-alcoholic fatty liver disease in the elderly: results from the Rotterdam study.J Hepatol. 2012;57:1305-1311.
[PubMed] [DOI][Cited in This Article: ]
Caballería L, Pera G, Auladell MA, Torán P, Muñoz L, Miranda D, Alumà A, Casas JD, Sánchez C, Gil D. Prevalence and factors associated with the presence of nonalcoholic fatty liver disease in an adult population in Spain.Eur J Gastroenterol Hepatol. 2010;22:24-32.
[PubMed] [DOI][Cited in This Article: ]
Mohan V, Farooq S, Deepa M, Ravikumar R, Pitchumoni CS. Prevalence of non-alcoholic fatty liver disease in urban south Indians in relation to different grades of glucose intolerance and metabolic syndrome.Diabetes Res Clin Pract. 2009;84:84-91.
[PubMed] [DOI][Cited in This Article: ]
Lai SW, Ng KC. Which anthropometric indices best predict metabolic disorders in Taiwan?South Med J. 2004;97:578-582.
[PubMed] [DOI][Cited in This Article: ]
Zhou YJ, Li YY, Nie YQ, Ma JX, Lu LG, Shi SL, Chen MH, Hu PJ. Prevalence of fatty liver disease and its risk factors in the population of South China.World J Gastroenterol. 2007;13:6419-6424.
[PubMed] [DOI][Cited in This Article: ]
Inabe F, Takahashi E, Moriyama K, Negami M, Otsuka H. Risk assessment chart for predicting fatty liver in Japanese subjects.Tokai J Exp Clin Med. 2012;37:94-101.
[PubMed] [DOI][Cited in This Article: ]
Wong VW, Chu WC, Wong GL, Chan RS, Chim AM, Ong A, Yeung DK, Yiu KK, Chu SH, Woo J. Prevalence of non-alcoholic fatty liver disease and advanced fibrosis in Hong Kong Chinese: a population study using proton-magnetic resonance spectroscopy and transient elastography.Gut. 2012;61:409-415.
[PubMed] [DOI][Cited in This Article: ]
Meier CR, Krähenbühl S, Schlienger RG, Jick H. Association between body mass index and liver disorders: an epidemiological study.J Hepatol. 2002;37:741-747.
[PubMed] [DOI][Cited in This Article: ]
Aune D, Greenwood DC, Chan DS, Vieira R, Vieira AR, Navarro Rosenblatt DA, Cade JE, Burley VJ, Norat T. Body mass index, abdominal fatness and pancreatic cancer risk: a systematic review and non-linear dose-response meta-analysis of prospective studies.Ann Oncol. 2012;23:843-852.
[PubMed] [DOI][Cited in This Article: ]
Singh S, Sharma AN, Murad MH, Buttar NS, El-Serag HB, Katzka DA, Iyer PG. Central adiposity is associated with increased risk of esophageal inflammation, metaplasia, and adenocarcinoma: a systematic review and meta-analysis.Clin Gastroenterol Hepatol. 2013;11:1399-1412.e7.
[PubMed] [DOI][Cited in This Article: ]
Ruhl CE, Everhart JE. Determinants of the association of overweight with elevated serum alanine aminotransferase activity in the United States.Gastroenterology. 2003;124:71-79.
[PubMed] [DOI][Cited in This Article: ]
Papatheodoridis GV, Goulis J, Christodoulou D, Manolakopoulos S, Raptopoulou M, Andrioti E, Alexandropoulos N, Savvidou S, Papachristou A, Zervou E. High prevalence of elevated liver enzymes in blood donors: associations with male gender and central adiposity.Eur J Gastroenterol Hepatol. 2007;19:281-287.
[PubMed] [DOI][Cited in This Article: ]
Kojima H, Sakurai S, Uemura M, Takekawa T, Morimoto H, Tamagawa Y, Fukui H. Difference and similarity between non-alcoholic steatohepatitis and alcoholic liver disease.Alcohol Clin Exp Res. 2005;29:259S-263S.
[PubMed] [DOI][Cited in This Article: ]
Hamano M, Kamada Y, Kiso S, Furuta K, Kizu T, Chatani N, Egawa M, Takemura T, Ezaki H, Yoshida Y. Adiponectin negatively correlates with alcoholic and non-alcoholic liver dysfunction: Health check-up study of Japanese men.Hepatol Res. 2013;43:238-248.
[PubMed] [DOI][Cited in This Article: ]
Gonzalez-Quintela A, Tomé S, Fernandez-Merino C, Rey J, Meijide L, Gude F. Synergistic effect of alcohol consumption and body mass on serum concentrations of cytokeratin-18.Alcohol Clin Exp Res. 2011;35:2202-2208.
[PubMed] [DOI][Cited in This Article: ]
Roberts EA. Pediatric nonalcoholic fatty liver disease (NAFLD): a “growing” problem?J Hepatol. 2007;46:1133-1142.
[PubMed] [DOI][Cited in This Article: ]
Lonardo A, Carani C, Carulli N, Loria P. ‘Endocrine NAFLD’ a hormonocentric perspective of nonalcoholic fatty liver disease pathogenesis.J Hepatol. 2006;44:1196-1207.
[PubMed] [DOI][Cited in This Article: ]
Ishibashi E, Eguchi Y, Eguchi T, Matsunobu A, Oza N, Nakashita S, Kitajima Y, Kuroki S, Ozaki I, Kawaguchi Y. Waist circumference correlates with hepatic fat accumulation in male Japanese patients with non-alcoholic fatty liver disease, but not in females.J Gastroenterol Hepatol. 2008;23:908-913.
[PubMed] [DOI][Cited in This Article: ]
Mann CJ. Observational research methods. Research design II: cohort, cross sectional, and case-control studies.Emerg Med J. 2003;20:54-60.
[PubMed] [DOI][Cited in This Article: ]
Wanless IR, Lentz JS. Fatty liver hepatitis (steatohepatitis) and obesity: an autopsy study with analysis of risk factors.Hepatology. 1990;12:1106-1110.
[PubMed] [DOI][Cited in This Article: ]
de Alwis NM, Day CP. Non-alcoholic fatty liver disease: the mist gradually clears.J Hepatol. 2008;48 Suppl 1:S104-S112.
[PubMed] [DOI][Cited in This Article: ]
Kim HJ, Kim HJ, Lee KE, Kim DJ, Kim SK, Ahn CW, Lim SK, Kim KR, Lee HC, Huh KB. Metabolic significance of nonalcoholic fatty liver disease in nonobese, nondiabetic adults.Arch Intern Med. 2004;164:2169-2175.
[PubMed] [DOI][Cited in This Article: ]
Tarantino G, Colicchio P, Conca P, Finelli C, Di Minno MN, Tarantino M, Capone D, Pasanisi F. Young adult obese subjects with and without insulin resistance: what is the role of chronic inflammation and how to weigh it non-invasively?J Inflamm (Lond). 2009;6:6.
[PubMed] [DOI][Cited in This Article: ]
Buechler C, Wanninger J, Neumeier M. Adiponectin, a key adipokine in obesity related liver diseases.World J Gastroenterol. 2011;17:2801-2811.
[PubMed] [DOI][Cited in This Article: ]
Schäffler A, Schölmerich J, Büchler C. Mechanisms of disease: adipocytokines and visceral adipose tissue--emerging role in nonalcoholic fatty liver disease.Nat Clin Pract Gastroenterol Hepatol. 2005;2:273-280.
[PubMed] [DOI][Cited in This Article: ]
Nobili V, Alisi A, Raponi M. Pediatric non-alcoholic fatty liver disease: preventive and therapeutic value of lifestyle intervention.World J Gastroenterol. 2009;15:6017-6022.
[PubMed] [DOI][Cited in This Article: ]
Chan DC, Watts GF, Gan SK, Ooi EM, Barrett PH. Effect of ezetimibe on hepatic fat, inflammatory markers, and apolipoprotein B-100 kinetics in insulin-resistant obese subjects on a weight loss diet.Diabetes Care. 2010;33:1134-1139.
[PubMed] [DOI][Cited in This Article: ]
Peng L, Wang J, Li F. Weight reduction for non-alcoholic fatty liver disease.Cochrane Database Syst Rev. 2011;CD003619.
[PubMed] [DOI][Cited in This Article: ]
Verna EC, Berk PD. Role of fatty acids in the pathogenesis of obesity and fatty liver: impact of bariatric surgery.Semin Liver Dis. 2008;28:407-426.
[PubMed] [DOI][Cited in This Article: ]
Said A. Non-alcoholic fatty liver disease and liver transplantation: outcomes and advances.World J Gastroenterol. 2013;19:9146-9155.
[PubMed] [DOI][Cited in This Article: ]