The Association between Helicobacter pylori Infection and Glycated Hemoglobin A in Diabetes: A Meta-Analysis

Background The association between Helicobacter pylori infection and glycated hemoglobin A has been confirmed in many studies, but these conclusions are still contradictory and controversial. Therefore, we conducted a meta-analysis to resolve the problem of inconsistent results in diabetes. Methods A comprehensive search was conducted on related researches published in PubMed, Embase, and China Academic Journal Full-text Database (CNKI) from the inception of each database to April 2019. Fixed or random effects model was used to pool the weighted mean difference with 95% confidence interval from individual studies. Subgroup and sensitivity analyses were also performed. Publication bias was estimated by funnel plot, Egger's test, and fail-safe numbers. Results 35 studies with 4,401 participants with diabetes were included in the meta-analysis. Glycated hemoglobin A levels were elevated in patients with Helicobacter pylori infection compared with patients without Helicobacter pylori infection (WMD = 0.50, 95% CI: 0.28-0.72, p < 0.001). In subgroup analysis by the subtype of diabetes, there was a correlation between Helicobacter pylori infection and elevated glycated hemoglobin A in type 1 diabetes (I2 = 74%, p < 0.001, WMD = 0.46, 95% CI: 0.12-0.80), and in type 2 diabetes (I2 = 90%, p < 0.001, WMD = 0.59, 95% CI: 0.28-0.90, p < 0.001). In subgroup analysis by the study design, there was a correlation in cross-sectional study (I2 = 89%, p < 0.001, WMD = 0.42, 95% CI: 0.16-0.69, p ≤ 0.003) and in case-control study (I2 = 83%, p < 0.001, WMD = 0.39, 95% CI: 0.14-0.64, p ≤ 0.003). By different methods for detecting Helicobacter pylori, there was a correlation in the biopsy group (I2 = 83%, p < 0.001, WMD = 0.6, 95% CI: 0.11-1.09, p ≤ 0.03) and in other groups of test methods (I2 = 87%, p < 0.001, WMD = 0.37, 95% CI: 0.17-0.56, p < 0.001). Sensitivity analysis showed that our results were reliable, and no evidence of substantial publication bias was detected. Conclusion The meta-analysis might indicate a correlation between Helicobacter pylori infection and glycated hemoglobin A levels in diabetes.


Introduction
In 2007, the International Federation of Clinical Chemistry (IFCC) clearly defined glycated hemoglobin A (HbA1c) as a stable adduct formed by glucose and the free amino group of the hemoglobin β chain-N-terminal proline [1]. In 2011, World Health Organization officially recommended HbA1c ≥ 6 5% as a diagnostic cutoff point for diabetes [2]. The American Diabetes Association (ADA) recommends that HbA1c should be measured in patients with newly developed diabetes, and it plays an important role in the monitoring of diabetes as an evaluation index to judge the effect of blood glucose control. Helicobacter pylori infection is now considered the most important cause of gastritis and peptic ulcer in humans. And studies have reported on the potential links between H. pylori infection and a variety of extra-gastroduodenal manifestations ischemic as heart disease, liver diseases, skin diseases, blood disorders, neurologic disorders, and others [3]. Christie et al. found serological evidence of H. pylori infection which was associated with an increased rate of incident diabetes in a Latino elderly cohort [4]. However, studies on the relationship between H. pylori infection and HbA1C in diabetic patients are inconsistent and sometimes contradictory. The finding of Bazmamoun et al. showed that there was no correlation between Helicobacter pylori infection and HbA1c levels [5]. Studies by Akın et al. found that HbA1c levels in Helicobacter pyloripositive patients were significantly higher than those in Helicobacter pylori-negative patients [6]. Due to these discrepancies, we performed a meta-analysis investigating the relationship between H. pylori infection and glycated hemoglobin A in patients with diabetes.

Methods
2.1. Literature Search Strategy. "Helicobacter pylori" and "glycated hemoglobin A" were jointly searched in PubMed database, the Embase database, and China National Knowledge Infrastructure (CNKI) as keywords for all relevant literature published before April 2019. Moreover, we also reviewed the reference not captured by our database search.

Inclusion
Criteria. The inclusion criteria were as follows: (1) observational studies; (2) studies are related to the relationship between H. pylori and diabetes, including case groups and control groups, and providing the exact sample size, the number of patients with H. pylori infection, and the mean and standard deviation of the level of HbA1c; (3) the diagnosis of diabetes was in agreement with international guidelines [7]; (4) H. pylori infection is judged by at least one diagnostic method; and (5) the studies are not directly related but with the abovementioned requirements.

Exclusion
Criteria. The exclusion criteria were as follows: (1) case report and observational studies without control groups; (2) studies in which the data of the level of HbA1c were not available for either diabetes group or control group; (3) subset of a published article by the same authors or repeated published literature; (4) studies limited to animal; and (5) the data of literature are incomplete with little information, and the extraction of original data is not enough to calculate the statistics of this study.

Study Selection.
Two researchers independently screened the literature, extracted the data, and cross-checked. If the results were inconsistent, those would be discussed together or judged by a third senior researcher. This study used preestablished data extraction forms to extract data from the literature that will eventually be included in the meta-analysis. The excerpts included the first author, the year of publication, the study area, the diagnostic criteria for H. pylori infection, the sample size of the case and control groups, and the mean and standard deviation of HbA1c.
2.5. Statistical Analysis. The data and the database were organized and checked carefully according to the requirements of the meta-analysis. RevMan 5.3 was used for statistical analysis, and weighted mean difference (WMD) with 95% CI was used for quantitative analysis of measurement data. I 2 was used to quantitatively test the heterogeneity among different studies. If I 2 ≤ 50%, the heterogeneity had no statistical significance, and fixed effects model was used to analyze it. On the contrary, if I 2 > 50% the heterogeneity had statistical significance, and random effects model was used to analyze. Moreover, subgroup analysis was carried out to explore the sources of heterogeneity according to the factors that might produce heterogeneity. To ensure the stability of the results of the meta-analysis, the sensitivity analysis (after the included studies removed one by one, the combined analysis was performed again, and the significant difference between the effect values before and after the combination was compared) was performed. The funnel plot, Egger's test, and fail-safe number were used to quantitatively evaluate the  publication bias. p < 0 05 was considered statistically significant, suggesting that publication bias is not excluded.

Publication Bias
Egger's test (p > 0 05) showed no significant publication bias. Funnel plot is basically symmetrical and has no publication bias ( Figure 6). Fail-safe numbers, indicating the publication bias, are reported in Table 2. The fail-safe numbers were all relatively large in the meta-analysis, suggesting that the results were reliable.

Discussion
The quantitative data of this meta-analysis showed that the level of HbA1c in the H. pylori-infected group was significantly higher than that in the H. pylori-negative group, indicating that H. pylori infection and HbA1c were correlated in diabetes. Subgroup analysis revealed that (1) Helicobacter pylori infection was correlated with the level of HbA1c in type 1 diabetes mellitus and type 2 diabetes mellitus. (2) According to the type of studies, they were divided into two subgroups: case-control study and cross-sectional study.  It is estimated that about 4.4 billion people worldwide were infected with H. pylori in 2015 [42], and it is estimated that diabetes will reach 552 million by 2020 [43]. Kato et al. have shown that H. pylori infection is associated with an increased risk of diabetes mellitus [44]. Refaeli et al. showed that the prevalence of metabolic syndrome in H. pyloriinfected patients was higher than that in uninfected patients [45]. More and more data indicated that inflammation may play a role in the pathogenesis of type 2 diabetes, and the pathogenesis of type 2 diabetes can be regarded as an autoinflammatory disease [46]. Simultaneously, the inflammatory response caused by H. pylori has also been confirmed by researches [47,48]. At the same time, studies have shown that eradication of H. pylori can improve glucose homeostasis in type 2 diabetes mellitus by reducing proinflammatory factors [49]. In addition, studies have shown that H. pylori can promote insulin resistance by inducing chronic inflammation and affecting insulin regulation of gastrointestinal hormones [50]. Gastritis caused by H. pylori may affect the secretion of gastric-related hormones, such as leptin and growth hormone-releasing hormone, as well as gastrin and somatostatin, which may affect the susceptibility to diabetes [51]. Studies have also described a positive correlation between H. pylori infection and impaired insulin secretion [52]. The results of Zhou et al. showed that H. pylori infection induced hepatic insulin resistance through c-Jun/miR-203/SOCS3 signaling pathway and provided possible implications for insulin resistance [53]. Although the mechanism of the association between H. pylori infection and diabetes   is still unclear, more and more studies have shown that there is a potential link between them. Because of the large number of patients with the two diseases, if the causal relationship between them becomes clear, the impact will be great. Meta-analysis is a secondary literature analysis based on previous research evidence. Therefore, there are limitations and biases in the analysis. Case-control studies are inevitably affected by selective bias. The results are not as reliable as prospective studies, and there are some limitations. Moreover, the results of this study are not grouped by population, region, and race. The limitation of this meta-analysis is that it does not consider other characteristics that may affect blood sugar control besides H. pylori infection, such as treatment status, age, gender, obesity index, or smoking status.
In conclusion, the results of this meta-analysis indicate that Helicobacter pylori infection is associated with increased glycosylated hemoglobin A, with a large sample size and a certain degree of confidence. Although some biases affect the accuracy of the results, it is still possible to provide new reference and guidance for eradication of H. pylori as a secondary prevention or treatment of diabetes. Proper screening for H. pylori infection and regular monitoring of blood glucose and HbA1c may be effective for early detection of blood glucose disorders and prevention of type 2 diabetes. Further research, especially longitudinal studies, is necessary to validate current results.

Conclusion
This study conducted a meta-analysis of existing literature and concluded that H. pylori infection may increase the level of glycosylated hemoglobin A in diabetic patients, and the  same conclusions were obtained in both type 1 diabetes and type 2 diabetes. The sample size included in this paper is large and has credibility, which can guide clinical work to a certain extent. In clinical practice, individualized prevention and treatment need to be closely combined with the actual situation of the patient.