The Association between Helicobacter Pylori Infection and Metabolic Syndrome in a Taiwanese Adult Population

Objectives: The global prevalence of Helicobacter pylori (H. pylori) infection remains high. Recent studies demonstrated the potential relationship among H. pylori-induced chronic inflammation, insulin resistance and metabolic disorders. The aim of this study was to investigate the association between H. pylori infection and metabolic syndrome (MetS). Methods: This cross-sectional study enrolled 4,232 health examination participants aged from 30 to 65-year-old in the northern Taiwan in 10 years. The general information and blood tests of all subjects were collected from the health examination center. H. pylori infection was diagnosed via 13C-urea breath test. The log-transformed (log) serum high sensitivity C-reactive protein (hs-CRP) was used as the inflammatory parameter. MetS was defined according to the revised National Cholesterol Educational Program Adult Treatment Panel III (Revised NCEP ATP III) criteria. Subjects were divided into two groups based on their H. pylori infectious status. The association between H. pylori infection and metabolic parameters was assessed with multivariate logistic regression analysis. Results: A total of 4,232 subjects (2,641 males and 1,591 females, aged 47.0 years ± 8.2 years) were enrolled for the analysis. H. pylori infection presented in 44.8% of all subjects. MetS presented in 27.6% of all subjects. Participants with H. pylori infection showed higher proportion of MetS, higher body mass index(BMI) and higher serum cholesterol(T-CHO) levels with statistical significance (p<0.001). There was no significant difference in the log serum hs-CRP between subjects with and without H. pylori infection. H. pylori infection increased the risk of large waist circumference component [OR=1.26 (1.10-1.43)] and high fasting plasma glucose component [OR=1.18 (1.04-1.34)], and contributed significantly to the presence of MetS with adjusted OR 1.23 (1.03-1.46). Conclusions: Adults with H. pylori infection was associated with higher prevalence of MetS, higher BMI and higher mean serum T-CHO levels. Furthermore, H. pylori infection was identified as a risk factor for MetS.


Introduction
The prevalence of Helicobacter pylori (H. pylori) infection remains high throughout global population [1,2]. Aside from causing gastrointestinal diseases, including chronic gastritis, peptic ulcers and gastric mucosa-associated lymphoid tissue lymphoma [3], recent studies also implied the potential relationship among the H. pylori infection, cardiovascular diseases and atherosclerosis [4,5]. Liu et al. in a meta-analysis demonstrated that H. pylori infection was associated with an increased risk of myocardial infarction regardless of age, race or socioeconomic status [6]. Another study conducted by Kowalski proposed a significant link between coronary artery disease and H. pylori infection. Patients infected with CagA-positive strains of H. pylori showed greater coronary artery lumen loss [7].
Metabolic syndrome (MetS) comprises multiple components of metabolic abnormalities tightly related to insulin resistance. Polyzos et al. in a systemic review indicated a trend toward a positive association between H. pylori infection and homeostatic model of assessment insulin resistance (HOMA-IR), which brought up a potential mechanism linking H. pylori infection and MetS [8]. Chronic inflammation induced by H. pylori infection may increase the release of multiple inflammatory cytokines and the development of insulin resistance, which act as risk factors for MetS [8][9][10]. However, the causal relationship between H. pylori infection and MetS remains unclear and the controversial results also exist [8,11].
A community-based cohort study revealed that H. pylori infection may increase insulin resistance and served as a predictor of MetS in a Taiwanese population [12]. The serostatus of anti-H. pylori IgG was used as diagnostic tool for H. pylori infection. However, previous studies have reported that serum anti-H. pylori IgG existed even after several years of H. pylori eradication, which couldn't accurately reflect the active infection [13,14]. Another cross-sectional study with a larger sample size using 13 C-urea breath test as diagnostic tool also demonstrated that H. pylori infection was positively associated with MetS, especially in females [15]. The average age of participants was younger (35.2 years)

Study population
This cross-sectional study enrolled 4,232 subjects aged from 30 years to 65 years who participated in their annual health examination in a health examination center in the northern Taiwan during the past 10 years, and was approved by the Institutional Review Board of MacKay Memorial Hospital prior to recruitment. Individuals with history of cancer or those who received H. pylori eradication therapy, proton pump inhibitors, bismuth or histamine type 2(H 2 ) receptor antagonists 1 month prior to enrollment were excluded. All the subjects were then divided into two groups according to their results of 13 C-urea breath test for subsequent analysis.

Data collection
The information of medical history, personal history, physical examination and blood tests of all subjects were collected from the health examination center. The written informed consents were obtained from the participants prior to data collection. Subjects with systemic disease, such as diabetes mellitus or hypertension were also registered.
Waist circumference (WC) was measured at the midline between the lowest border of the subcostal rib and the superior border of the iliac crest. Body mass index (BMI) was measured as weight divided by height squared (kg/m 2 ).
Alcohol consumption was defined as regular daily alcohol intake. Current smoking was defined as regular daily smoking. Exercise was defined as having daily exercise habits. The presence of H. pylori infection was based on the results of 13 C-urea breath test. The logtransformed (log) serum high sensitivity C-reactive protein (hs-CRP) value was used as the parameter of chronic inflammation. Blood samples of all subjects were collected after overnight fasting and were immediately analyzed for biochemistry tests.
MetS was defined according to the revised National Cholesterol Educational Program Adult Treatment Panel III (revised NCEP ATP III) criteria. (Presence of at least three of the following five traits: 1) Abdominal obesity, defined as a WC in men and women of ≧ 90 cm and ≧ 80 cm, respectively; 2) serum triglycerides (TG) ≧ 150 mg/dL or drug treatment for elevated TG; 3) serum high-density lipoprotein cholesterol (HDL-C) <40 mg/dL in men and <50 mg/dL in women or drug treatment for low HDL-C; 4) blood pressure (BP) ≧ 130/85 mmHg or drug treatment for elevated BP; or 5) fasting plasma glucose (FPG) ≧ 100 mg/dL or drug treatment for elevated blood glucose [16].

Statistical Analysis
Data were presented as mean ± SD or as percentages. Statistical analysis was performed using SPSS version 24.0 (SPSS Inc., Chicago, IL). Categorical data were analyzed with the chi-squared test, and continuous data were analyzed with the independent samples t-test. Six models were proposed to assess the association between H. pylori infection and metabolic parameters by multivariate logistic regression analysis. Model 1 showed the association between H. pylori infection and MetS adjusted for age, gender, BMI, presence of hypertension and diabetes mellitus. Model 2 to model 6 showed the relationship between H. pylori infection and each component of MetS adjusted for age and gender. The odds ratios (OR) and 95% confidence intervals (CI) were calculated. A two-tailed p-value <0.05 was considered statistically significant.

Results
A total of 4,232 subjects (2,641 males and 1,591 females, aged 47.0 ± 8.2 years) were enrolled for the analysis. 13 C-urea breath test showed positive in 44.8% of all subjects. MetS was present in 27.6% of all subjects. Diabetes mellitus and hypertension were present respectively in 6.6% and 18.5% of all cases. Subjects were categorized into two groups according to their H. pylori infectious status. The characteristics of demographic data are shown in Table 1.

Discussion
The aim of this study is to investigate the association between the H. pylori infection and MetS, furthermore, its predictive role. To our knowledge, this is also the first study applying 13 C-urea breath test as the diagnostic assay to explore the inflammatory process linking H. pylori infection and MetS. We defined H. pylori infection based on the results of 13 C-urea breath test, which has proven to be a more accurate diagnostic assay for active infection compared to traditional serology used in most epidemiologic studies [17]. It was found that subjects with H. pylori infection presented higher prevalence of MetS, higher BMI and higher mean serum T-CHO. Regarding each component of MetS, the proportion of large WC, high BP and high FPG were also higher in those with H. pylori infection. In addition, multivariate logistic regression analysis demonstrated that H. pylori infection contributed significantly to the presence of MetS and two of its five components (large WC and high FPG) after adjusting potential confounders.
There is growing evidence indicating a close relationship among chronic infection, cardiovascular diseases and MetS. Chronic pathogen exposure could contribute to the development of atherosclerosis and insulin resistance by numerous mechanisms, including promotion of endothelial dysfunction and induction of a systemic inflammatory state. The major organisms that have been suggested include Chlamydia pneumoniae, cytomegalovirus and H. pylori. Besides, coxsackie viral infection, hepatitis A virus, and herpes simplex virus type 1 and type 2 have also been proposed [18,19].
According to previous reports, over 50% of the world's population was infected by H. pylori, with higher rate in the developing countries [1,2,5]. Some epidemiologic studies also indicate most infections could be acquired since childhood [1,20]. In a Taiwanese research, a total of 54.4% of participants presented with H. pylori infection, with similar prevalence between both genders [21]. Our result showed slightly lower prevalence compared to previous results. Potential risk factors of acquiring H. pylori infection include socially deprived environment and lower social economic status [22,23]. Participants recruited in this study comprised those with relatively higher social economical class. Thus, their professional background may have an influence on the prevalence of H. pylori infection. In addition, diagnosis in the former report was based on serologic tests, which may cause a higher falsepositive rate than the 13 C-urea breath test used in our study.
The development of MetS is mediated by multiple factors. The visceral obesity and the insulin resistance are considered to play the core roles [24,25]. Meanwhile, the visceral obesity also disturbs the balance of pro-inflammatory cytokines. Increased release of these cytokines contributes to a chronic inflammatory state, which affects metabolic risk factors, including blood pressure, lipid profile and glucose intolerance [18,[26][27][28]. Indeed, recent studies also include inflammatory state as a component of MetS, which implies the tight correlation between chronic inflammation and MetS [29,30]. In our results, H. pylori infection increased the risk of large WC and high FPG, which may reflect its impact on the visceral obesity and the insulin resistance.
Although the definite pathogenetic association between H. pylori infection and MetS has not been well established, some potential mechanisms have been proposed in previous studies. Chronic bacterial infection may trigger the secretion of pro-inflammatory cytokines such as hsCRP, tumor necrosis factor-α (TNF-α), interleukins and interferon-γ, which are involved with atherosclerosis, insulin resistance and lipid metabolism [8,9,12]. In a study performed by Takeoka et al., H pylori-associated gastritis was also identified as a risk factor for MetS, which further strengthened the link between H pylori-related inflammation and metabolic disorders [31]. Besides, gastric H. pylori colonization alters the balance of certain gastrointestinal hormones, including ghrelin and leptin, which could impair insulin homeostasis and lead to weight gain and fat accumulation [32]. Furthermore, H. pylori infection also affects the composition of the gut microbiota, mediating the development of obesity, systemic inflammation, and insulin resistance [33,34]. In our results, H. pylori infection increased the risk of large WC and high FPG components, which correspond to previous hypothesis and may reflect its impact on the visceral obesity and the insulin resistance.
In our study, we also investigated the potential relationship between H. pylori-associated inflammation with MetS by using log serum hsCRP as the inflammatory parameter. Subjects presented no significant difference in the log serum hsCRP values between two groups, which was similar to previous results. In the study carried out by Chen et al. subjects with positive anti-H.pylori IgG exhibited higher level of TNF-α than those without H. pylori antibodies. But there was no significant difference among other inflammatory cytokines including hsCRP [12]. In our study, we used log serum hsCRP as the inflammatory parameter. Subjects presented no significant difference in the log serum hsCRP values between two groups, which was similar to previous results. Considering that most individuals acquire H. pylori infections since childhood, the impact on inflammatory process and MetS may vary among different age groups and hinder the interpretation of our results. Further research was required to explore the detailed involvement of different cytokines mediated between H. pylori infection and metabolic disorders. BMI, HOMA-IR, systolic blood pressure and lower HDL-C, most of which were compatible to the results in our study [35]. However, previous reports showed some inconsistencies regarding different components of MetS affected by H. pylori infection. In our study, two of five components of MetS(Large WC and high FPG) reached significant difference between subjects with and without H. pylori infection. After adjusting for covariates, logistic regression models indicated that H. pylori infection increased the risk of two components of MetS. This discrepancy may result from the different virulent strains of H. pylori or the diverse host genetic factors [15]. For example, CagA-positive strains of H. pylori have been found to associate with a higher average glycated hemoglobin level in adults [32]. In addition, different criteria adopted for MetS and various diagnostic tests used for H. pylori infection in different studies also affect the interpretation of results.
Aside from various metabolic parameters influenced by H. pylori infection proposed in previous studies, several reports also raised the concern of decreasing metabolic risk factors by H. pylori eradication.
In a large prospective cohort study conducted by Nam et al., improved lipid profile was observed in patients with H. pylori infection 1~3 years after eradication therapy [36]. In another study carried out by Gen R et al., the HOMA-IR, lipid profile and CRP levels in individuals after successful eradication significantly improved from the pretreatment status, which provided favorable perspective for reducing the incidence of MetS and its associated morbidity [37]. However, significant discrepancy and heterogeneous results impede the consistency among different studies. Further large-scale prospective researches with more stringent standards are indicated to determine the actual effects of eradication therapy on metabolic disorders in real-world.
In our study, H. pylori infection was identified as a risk factor for MetS. Furthermore, H. pylori infection also increased the risk of large WC and high FPG, which were considered as core factors of development of MetS. However, the concrete mechanism regarding the potential role of treating and preventing MetS by H. pylori eradication still needs to be clarified.
There were several limitations in this study. First, this was a singlecenter retrospective study. Thus, the composition of participants may pose unmeasured confounding factors or selection bias for this study. The self-reported collection system of medical history could also mislead the interpretation of our results. Second, although 13

Conclusion
In this study, adult subjects with H. pylori infection exhibited higher prevalence of MetS with two main components reaching significant difference (large WC and high FPG). Higher BMI and mean serum T-CHO were also observed in those with H. pylori infection. H. pylori infection was an independently predictive risk factor for MetS, as well as its two components (large WC and high FPG), which may reflect its negative impact on obesity and insulin resistance. The adjusted OR of MetS with H. pylori infection was 1.23 (95% CI, 1.03-1.46, p=0.023).
The detailed mechanism and pathophysiology regarding various degrees of different metabolic components influenced by H. pylori infection remain to be investigated. In addition, further study was required to establish the comprehensive causative link between H. pylori infection and MetS. Finally, aside from preventing some digestive disorders and certain neoplasms, H. pylori eradication treatment may also have the therapeutic potential on MetS and its associated comorbidity, including obesity, dyslipidemia, insulin resistance and hypertension.