Table 1 The relevant studies on the associations between H. pylori infection and extra-gastroduodenal diseases

Iron deficiency anemia (IDA)

Pros:

1. Qu et al. [19]: an increased risk of IDA in patients with H. pylori infection (meta-analysis of case-control studies).

2. Yuan et al. [21]: Eradication of H. pylori could improve the levels of hemoglobin and serum ferritin in patients with IDA (meta-analysis of intervention trials).

Cons:

1. Sandstrom et al. [18]: no association between H. pylori infection and IDA in female adolescents (case-control study).

Eradication of H. pylori infection is recommended for patients with unexplained IDA.

Immune thrombocytopenic purpura (ITP)

Pros:

1. Stasi et al. [35]: The overall response rate of increased platelet count was 50.3% after successful eradication of H. pylori in ITP patients (meta-analysis of intervention trials).

2. Arnold et al. [37]: The odds of achieving a platelet count response following eradication therapy were 14.5 higher in ITP patients with H. pylori infection than in those without infection (response rate: 51.2% vs. 8.8%) (meta-analysis of intervention trials).

Cons:

1. Michel et al. [34]: Seroprevalence of H. pylori in patients with ITP was not significantly different from that in control subjects (case-control study).

H. pylori infection should be sought and treated in patients with ITP.

Vitamin B12 deficiency

Pros:

1. Sarari et al. [44]: There was significant association between the presence of H. pylori infection and vitamin B12 deficiency (case-control study).

2. Shuval-Sudai et al. [45]: Prevalence of H. pylori seropositivity was significantly higher among subjects with borderline (> 145–180 pg/mL) or low normal (> 180–250 pg/mL) vitamin B12 levels than among those with vitamin B12 > 250 pg/mL (case-control study).

H. pylori infection is associated with vitamin B12 deficiency.

Metabolic syndrome and diabetes mellitus (DM)

Pros:

1. Chen et al. [48]: H. pylori-infected subjects had a higher prevalence of metabolic syndrome than those without H. pylori infection (case-control study).

2. Yang et al. [49]: H. pylori infection was associated with risk of DM (case-control study).

Cons:

1. Naja et al. [53]: no association between H. pylori infection and metabolic syndrome (case-control study).

2. Wada et al. [55]: The eradication of Helicobacter pylori does not affect glycemic control in Japanese subjects with type 2 diabetes (intervention trial).

The association between H. pylori infection and metabolic syndrome or DM is contradictory.

Nonalcoholic fatty liver disease (NAFLD)

Pros:

1. Kim et al. [61]: The subjects with H. pylori infection had a higher incidence of NAFLD than those without infection (cohort study).

2. Wijarnpreecha et al. [65]: a significantly increased risk of NAFLD in patients with H. pylori infection (meta-analysis of case-control studies).

Cons:

1. Okushin et al. [63]: no association between H. pylori infection and NAFLD (case-control study).

The association between H. pylori infection and NAFLD remains contradictory.

Coronary artery disease (CAD)

Pros:

1. Yu et al. [73]: significant association between H. pylori infection and the risk of myocardial infarction (meta-analysis of case-control studies).

Cons:

1. Schottker et al. [75]: no association between H. pylori infection and the risk of CAD (cohort study).

The association between H. pylori infection and CAD is contradictory.

Cerebrovascular disease

Pros:

1. Wang et al. [81]: significant association between H. pylori infection and non-cardioembolic stroke (meta-analysis of case-control studies).

Cons:

1. Chen et al. [82]: a reverse link between H. pylori infection and stroke mortality (cohort study).

There is controversial evidence linking H. pylori infection and cerebrovascular disease.