What Do the Stomach and Esophagus Do? — A Pouch That Holds Acid, and Its Two Doors

People Who Wake Up with Heartburn at Night

Some people eat dinner, go to sleep, and wake up because the middle of their chest feels like it is burning. Sour fluid sometimes rises all the way up to the throat. People who experience this once a week or more are estimated at 13.3% of the population aged 15 and older, and there are large differences between countries (PMID 28232473).

Other people get a stomach exam during a health checkup and receive a few unfamiliar names written on their report. They also hear that there is a bacterium living inside the stomach. Roughly half of the world's population carries that bacterium (PMID 37081005).

The stomach holds an acid strong enough to dissolve food. But why does the stomach not dissolve itself? Why is the acid that should be in the stomach felt toward the chest? And what does the bacterium living in the stomach do?

This article follows what happens while swallowed food goes down from the throat to the stomach and stays in the stomach, and looks at three troubles that commonly arise along that path. The stories about stomach cancer and stomach checkups are written with Korean data and Korean guidelines, and the judgment on whether to get a checkup is looked at through how the European and American guidelines diverge. The big picture from mouth to anus is handled by the installment of this series that covers the big picture of digestion, and this article takes a closer look at the front part of that path.

The Path Swallowed Food Travels Down

The digestive tract is a single long tube running from the mouth to the anus, the path where food is broken down and absorbed as it passes. The section that swallowed food travels through first in this tube has a name. The esophagus is a muscular tube running from the throat through the chest to the stomach, the path that sends swallowed food down to the stomach.

At the end of the esophagus is the stomach. The biggest job the stomach takes on is preparing food so it can be digested and absorbed in the intestines, and at the center of that preparation is acid (PMID 21889024). Gastric acid is a strong acid secreted by the cells of the stomach wall, which prepares proteins for digestion and reduces the bacteria that enter with food. While the clump of food stays in the stomach, it is submerged in this acid, and thanks to that, digestion becomes easier (PMID 21889024). Gastric acid also helps iron, calcium, and vitamin B12 get absorbed (PMID 27607343).

The cells that produce the acid work by receiving signals from nerves and various hormones. These signals push and pull on the acid, adjusting it so that as much comes out as is needed for digestion and not enough to damage the walls of the stomach and the intestines below it (PMID 31670611).

The stomach has two gates. One is the entrance gate where food comes in from the esophagus, and the other is the exit going out from the stomach into the intestines. The stomach does not dump the kneaded food out through the exit all at once, but sends it out a little at a time. Gastric emptying is the job in which the stomach sends food down into the intestines. Beyond the exit is the small intestine. The small intestine is a narrow and long tube between the stomach and the large intestine, and most of the nutrients in food are absorbed here.

To sum up, the stomach is a pouch that holds food, submerge it in acid to knead it, and then sends it down little by little, and that pouch has an entrance gate and an exit gate.

A Pocket That Does Not Dissolve in Its Own Acid

Stomach acid is strong enough to kill swallowed bacteria (PMID 27607343). The wall of the stomach that makes that acid withstands the same acid all day long.

The gastric mucosa is a thin layer covering the inner wall of the stomach, where cells that make acid and mechanisms that protect the stomach from that acid live together. The gastric mucosa constantly maintains defenses against acid, and only when these defenses stay intact does the stomach wall avoid ulcers (PMID 21889024). The first layer of defense is sticky mucus covering the mucosal surface and an alkaline substance beneath that mucus that neutralizes acid. The components of mucus are still being studied today as substances that protect the mucosa and are involved in healing wounds (PMID 25229259). The acid-producing cells themselves release substances that regenerate the mucosa, sharing the tasks of making acid and protecting and repairing the stomach (PMID 31670611).

The wall of the esophagus is not built to be constantly bathed in stomach acid. The esophagus protects itself with the power to sweep back up what has risen and soften the acid, alongside the endurance of the wall itself (PMID 29037470).

At the spot where the esophagus and stomach meet, there is a doorway. The lower esophageal sphincter is a muscle wrapped in a ring at the very bottom of the esophagus where it meets the stomach, acting as a door that stays closed normally and opens when swallowed food comes down. This door and its surrounding structures form a barrier that keeps the contents of the stomach from rising backward into the esophagus (PMID 29037470) (PMID 40562014).

The stomach is a pouch equipped with defenses to endure its own acid, and in front of the esophagus, which lacks those defenses, stands a muscular door.

When the Door Loses Its Grip — Gastroesophageal Reflux Disease

What happens to a person who wakes up at night with a burning chest has a name. Gastroesophageal reflux disease (GERD) is a condition where stomach contents flow backward into the esophagus, causing troublesome symptoms or complications. Heartburn is a burning sensation behind the breastbone. The hallmark symptoms of this condition are heartburn and the regurgitation of stomach contents up to the throat or mouth (PMID 34326345).

This condition is common. In an analysis pooling 102 studies, the global average prevalence was 13.98%, ranging from 4.16% in China to 22.40% in Turkey depending on the country (PMID 32242117). Obesity, smoking, and an innate predisposition increase the risk (PMID 33351048), and symptoms were more common in people aged 50 or older, smokers, or those with obesity, but the researchers noted that the association was not large (PMID 28232473).

The causes are manifold. The entry door opening briefly when it is not time to swallow, weakening of the structures around the door, weak esophageal motility, delayed stomach emptying, and a pressure difference between the chest and abdomen are cited together (PMID 40562014). The amount of time the esophagus is exposed to stomach contents is the biggest factor determining the severity of this condition (PMID 29037470).

There are also differences in how people perceive it. Even if the amount flowing up is normal, symptoms and complications occur if the esophageal wall is weak or the esophagus is sensitive (PMID 29037470). An expert review by the American Gastroenterological Association (AGA) notes that as many as half of patients suspected of reflux do not improve with treatments that reduce stomach acid (PMID 35123084).

Diagnosis is usually based on symptoms and response to treatment. Diagnosis can often be made on typical symptoms alone (PMID 33351048), and in actual clinical practice, it is common to diagnose based on whether symptoms improve with reflux-reducing treatment, but an endoscopy and reflux monitoring tests are needed for a more precise diagnosis (PMID 34326345). A consensus statement from five Italian societies, including the Italian Society of Digestive Endoscopy (SIGE), also supports symptom-based diagnosis (PMID 40450492).

Endoscopy is a procedure where a thin tube with a camera at the tip is inserted through the mouth to directly view the inside of the esophagus and stomach. Guidelines place this test in specific situations. Difficulty swallowing, weight loss, and bleeding are symptoms classified as warning signs suspecting cancer, and one review notes that people with these signs or other risk factors such as older age, male sex, or obesity should undergo endoscopy (PMID 33351048). American Society for Gastrointestinal Endoscopy (ASGE) guidelines suggest endoscopy when warning signs are present (PMID 39692638), and the Italian consensus recommends endoscopy when warning signs are present and when there is no response to acid-reducing medications (PMID 40450492). The form with no visible damage to the esophagus even upon endoscopic examination is the most common presentation of this disease (PMID 34326345). Diagnosis of this condition is usually based on symptoms and treatment response, and endoscopy is used in specific situations such as the presence of warning signs or a lack of response to treatment.

Treatment is divided into lifestyle modifications, medications, and surgery, with acid-reducing medications being the most common (PMID 33351048). ASGE guidelines recommend using these medications at the lowest possible dose and for the shortest possible time (PMID 39692638). There is debate surrounding the harms of long-term use of these medications. Results showing that intestinal infections, fractures, kidney disease, and dementia were more common in long-term users mostly came from observational studies comparing medication users and non-users, and causality is not always confirmed (PMID 41010960). There are also evaluations that the quality of evidence for associations with kidney disease and dementia is very low (PMID 27607343). One review noted that confirmation is needed before these findings are reflected in clinical decisions, while also stating that long-term users should be re-evaluated while monitoring for harms (PMID 33351048), and guidelines emphasize periodically re-evaluating long-term medications and tapering or discontinuing them when appropriate (PMID 41010960).

Barrett's esophagus is a condition where the cells in the inner lining of the lower esophagus are replaced by cells of a different shape from the original. It appears in 2.3–8.3% of people with reflux disease and 1.2–5.6% of people without it, and the rate at which adenocarcinoma, a type of esophageal cancer, develops among people with Barrett's esophagus is 0.2–0.5% per year, or 2 to 5 out of every 1,000 people each year (PMID 35972481). American College of Gastroenterology (ACG) guidelines view Barrett's esophagus as a common condition associated with chronic reflux and the only known precursor to this cancer (PMID 35354777), and while guidelines recommend endoscopic surveillance, randomized trials comparing its effectiveness have not yet been conducted (PMID 35972481).

Bacteria That Live Inside a Pocket

These bacteria living in the human stomach, which is full of acid, were discovered in the early 1980s by two researchers named Marshall and Warren (PMID 33765303). These bacteria were first described as causing disease in 1983 (PMID 40924085). Helicobacter pylori are bacteria that settle down and live in the human stomach (PMID 33765303). Following this discovery, studies viewing these bacteria as the cause of disease poured in.

There is a mechanism for bacteria to live inside acid. These bacteria have a strong enzyme that protects them from acid, move with hair-like tails, and attach to the stomach wall with surface proteins (PMID 39725863).

About half of the world's population is infected, but there are large differences depending on the region and level of sanitation. They are usually caught when young, and if left untreated, they stay for life (PMID 37081005). An international consensus statement from 2025 reports that they are mainly transmitted within families (PMID 40912906), and transmission decreases as living conditions improve (PMID 36598803).

Most infected people have no symptoms (PMID 39725863). However, these bacteria cause gastritis in the stomach where they have settled (PMID 39725863). Gastritis is inflammation in the stomach lining. Gastritis is very common. The Korean guidelines for the treatment of gastritis note that because there is a lot of evidence that Helicobacter infection is linked to stomach cancer and that getting rid of the bacteria can prevent stomach cancer, Helicobacter-induced gastritis has been especially emphasized recently (PMID 40502844).

Helicobacter is common and mostly quiet, but inflammation takes root in an infected stomach.

When Inflammation Lasts — The Roads That Lead to Stomach Cancer and the Ones That Don't

Helicobacter is classified in Group 1 by the International Agency for Research on Cancer as something that causes cancer in humans (PMID 23981572). When gastritis lasts a long time, the organization of the stomach can change.

Atrophic gastritis is a state where the stomach's glands disappear amidst long-running inflammation (PMID 34454714). The stomach's glands are small structures inside the stomach wall that make and release stomach acid and digestive juices, and the cause of these glands shrinking is mostly a Helicobacter infection or cases where the body's immunity attacks its own stomach. Atrophy is a major factor that encourages stomach cancer (PMID 33785282), and a change where the stomach lining shifts to resemble the lining of the intestine can overlap on top of that (PMID 37652306). Doubts have recently been raised about the old model that steps forward one by one from inflammation to atrophy, to a change resembling the intestine, and to cancer, and the authors of one review see the evidence supporting this model as strong (PMID 37652306).

Only some people go all the way down that road. One review notes that roughly 20% of infected people experience pre-cancerous changes of the stomach during their lives, and stomach cancer develops in about 2% (PMID 32765194). These are rough estimates from a single review that does not disclose the population and time period. Helicobacter infection is cited as the biggest cause of stomach cancer, but stomach cancer does not develop in the vast majority of infected people (PMID 37652306) (PMID 32765194).

Even if pre-cancerous changes are seen, the weight is different. The 2025 guidelines from three European societies, including the European Society of Gastrointestinal Endoscopy (ESGE), note that for people whose atrophy or intestinal-resembling changes stay mild only near the exit side of the stomach and who lack other risk factors like a family history or a remaining Helicobacter infection, there is no separately set surveillance schedule, and that the vast majority of people met in clinical practice fall into this group. The same guideline recommends that people with widespread or advanced changes be monitored with endoscopy every 3 years (PMID 40112834).

How Much Does Eradicating the Bacterium Reduce Stomach Cancer?

Eradication therapy is a treatment that uses a combination of multiple antibiotics and acid-reducing medications to eliminate Helicobacter from the stomach. The backbone of the treatment is a combination of strong acid-reducing drugs and antibiotics, and because cases where the primary antibiotics used for this bacterium do not work have increased significantly, monitoring and careful use have become necessary (PMID 37081005).

Whether this treatment reduces stomach cancer has been evaluated using two tools. A randomized controlled trial is a study in which participants are randomly divided like a draw to give medication to only one side and compare the results with the other side. A meta-analysis is an analysis that gathers the results of multiple studies addressing the same question and recalculates them together.

In a 2020 meta-analysis gathering seven randomized controlled trials involving 8,323 healthy infected individuals, the group that received eradication therapy had a stomach cancer occurrence rate 0.54 times that of the group that did not (PMID 32205420). This magnitude means that for every 72 people treated, one case of stomach cancer is prevented, and in each trial followed for over two years, only a small number of people developed stomach cancer even in the untreated group. The proportion of deaths from stomach cancer was also lower at 0.61 times, but deaths combining all causes did not change (PMID 32205420). The authors rated this evidence as "moderate" and limited their conclusion to healthy people in East Asian countries and patients who had been treated for gastric tumors. Side effects of the treatment were not adequately reported in this analysis (PMID 32205420).

In a 2025 analysis recalculated with studies up to 2024, the results of eight trials targeting healthy infected individuals showed 0.64 times, and stomach cancer deaths across five trials showed 0.78 times. In eleven observational studies that simply followed people, the direction was similarly 0.56 times (PMID 39824392). A 2016 analysis gathering 24 studies, including observational ones, concluded that the benefit was greater the more prevalent stomach cancer originally was in a region, but that there was a benefit at all levels, even in low-risk regions (PMID 26836587). Evidence continues to accumulate that eradication therapy reduces the risk of stomach cancer in infected individuals, and the magnitude of the benefit depends on how common stomach cancer originally is in that region.

Regarding this evidence, two international consensus meetings were held in Taipei. The 2025 consensus statement, which adopted only sentences agreed upon by at least 80% of 32 experts from 12 countries, viewed Helicobacter as the main cause of stomach cancer and concluded that eradication therapy should be offered to all infected adults. The same consensus statement noted that testing for infection should start with high-risk groups, and that the risk decreases the most when the bacterium is eliminated before changes representing precancerous stages of the stomach occur (PMID 40912906). For changes resembling the intestine that have already taken root, the effect of eradication, even if present, is not large (PMID 37652306).

There is also another side to eradication. A 2025 meta-analysis reported that gastroesophageal reflux disease occurred more frequently after eliminating the bacterium, and the authors concluded that eradication increases that risk. However, 18 out of the 21 included studies were observational studies that merely followed people, so this conclusion is a pooling of associations from observational research (PMID 40662427). The 2025 consensus statement noted that eradication does not increase the risk of esophageal adenocarcinoma caused by reflux, and left the long-term impacts of heavy antibiotic use on other bacteria living in the body and antibiotic resistance as a task for further research (PMID 40912906).

When the Stomach Wall Caves In — Peptic Ulcer

In the United States, about 54,000 people are hospitalized each year for bleeding ulcers (PMID 39466269). A peptic ulcer is a sore where the inner wall of the stomach or duodenum has worn away and dug deep. The duodenum is the first part of the small intestine that connects right after the exit of the stomach.

The two major causes of this disease are Helicobacter infection and nonsteroidal anti-inflammatory drugs (PMID 38767885). Nonsteroidal anti-inflammatory drugs are a group of pain-relieving anti-inflammatory drugs widely used to reduce pain, fever, and inflammation. An American review attributes ulcers to Helicobacter in about 42% of patients and to these pain relievers, including aspirin, in about 36% (PMID 39466269). There are cases where the two overlap (PMID 30611829), and ulcers that fall under neither cause, which have become new challenges in diagnosis and treatment (PMID 28242110).

When people think of ulcers, many think of stress or spicy food. The reviews this article relies on did not measure the shares of those two separately, pointing instead to Helicobacter and pain-relieving drugs as the main causes. A 1994 review already noted chronic gastritis caused by Helicobacter as an important factor in duodenal ulcers (PMID 7502522). Since then, ulcers have dropped by more than half over the past 20 years, and the reasons cited for this are Helicobacter treatment, the careful use of pain-relieving drugs, and the widespread use of stomach-acid-reducing drugs (PMID 38767885).

About two-thirds of people with ulcers have no symptoms, and when symptoms are present, upper belly pain is the most common (PMID 30611829). It can also first reveal itself through complications such as bleeding, perforation of the stomach wall, or narrowing of the exit (PMID 37365037). Bleeding in the stomach, esophagus, and duodenum is a common reason older adults are hospitalized, and if not handled properly, it often deepens the illness or leads to death. Older age, Helicobacter infection, medication use, smoking, and a history of liver disease are cited as risk factors (PMID 33213769). Peptic ulcers are linked to an increase in hospitalizations and deaths (PMID 39466269). The standard for diagnosis is endoscopy, especially in older adults and those with warning signs (PMID 38767885).

Addressing the cause reduces recurrence. Stomach-acid-reducing drugs heal 80 to 100% of ulcers within 4 weeks. Eradicating Helicobacter drops the recurrence rate from 50 to 60% down to 0 to 2%, and when pain-relieving drugs are stopped, 95% of ulcers heal and recurrence drops from 40% to 9% (PMID 39466269). Other approaches for people who find it difficult to stop those drugs are found in the Japanese Society of Gastroenterology (JSGE) guidelines (PMID 33620586). The two major causes of peptic ulcers are Helicobacter and pain-relieving drugs, and addressing the causes greatly reduces recurrence.

After Dinner — Two Gates

We follow a person eating dinner. The swallowed food travels down the esophagus, and the lower esophageal sphincter opens to let the food into the stomach and then tightens again.

In the stomach, cells receiving signals from nerves and hormones secrete stomach acid (PMID 31670611). The food is soaked in that acid and churned into a paste (PMID 21889024), while the stomach lining maintains its defense amidst the same acid (PMID 21889024). The stomach pushes out the churned food a little at a time through the exit, passing it into the duodenum.

Meanwhile, the gate at the entrance sometimes relaxes briefly even when it is not time to swallow. This relaxation of the gate, delayed stomach emptying, and the pressure difference between the chest and abdomen are items listed as causes of reflux (PMID 40562014). When these events happen frequently, or when the barrier weakens and the strength to sweep up what has risen into the esophagus and neutralize the acid decreases, the time the esophagus contacts the stomach contents grows longer (PMID 29037470). Even when the exact same thing happens, the degree to which a person feels it as pain varies from individual to individual (PMID 29037470).

Even if Helicobacter pylori lives in this person's stomach, most people feel nothing, yet inflammation takes hold in the stomach all the while (PMID 39725863). What we followed in this scene are two gates. The entrance gate blocks acid from rising backward into the esophagus, and the exit sends the churned food down into the intestine little by little.

Stomach Cancer and Stomach Screening in Korea

The Korean clinical practice guidelines for gastritis state that the incidence of stomach cancer in Korea is the highest in the world (PMID 40502844). Stomach cancer was the most common cancer in Korea until 2018 (PMID 40502340), and the incidence of stomach cancer in Korean men living in the United States is more than five times that of non-Hispanic white men (PMID 25605140).

That number is coming down. Age-adjusted stomach cancer incidence rates from national cancer registration data fell from 43.0 per 100,000 population in 2011 to 29.6 in 2019, mortality dropped from 23.9 in 1999 to 6.7 in 2019, and the 5-year relative survival rate for stomach cancer patients rose from 55.7% in 1999–2005 to 77.0% in 2013–2019 (PMID 35938363). A study analyzing mortality statistics from 2000 to 2020 by age, period, and birth cohort concluded that the drop in mortality was largely explained by generational differences—where those born later had lower mortality rates—and that generational differences explained the decrease in mortality more than changes that occurred simultaneously across all ages during the same period (period effect) (PMID 36097804).

Korea’s national stomach cancer screening began in 1999 (PMID 40502340), offering adults aged 40 and older either an upper endoscopy or an upper gastrointestinal series every two years (PMID 35568752). In 2021, approximately 7.76 million endoscopies were performed through this screening, and 37.2% of the 29,361 stomach cancer cases that year were diagnosed via this screening (PMID 40502340). As of 2014, Korea and Japan were among the few countries with such screening programs (PMID 25505712).

The effectiveness of screening has mainly been evaluated using observational data. The authors of a 2024 review summarizing the outcomes of stomach cancer screening in Korea evaluated that screening endoscopy contributed to the early detection of stomach cancer and a reduction in mortality (PMID 40502340). The authors of the 2022 national cancer statistics report also concluded that since the national cancer screening program began in 2002, early-detected cancers and survival rates have increased, demonstrating the effectiveness of the national cancer control program (PMID 40083085).

In nationwide data following 46,701 patients diagnosed with stomach cancer between 2008 and 2009 for over 10 years, patients who had undergone screening prior to diagnosis had a lower rate of dying from stomach cancer than those who had never undergone it (53% lower risk) (PMID 35568752). Because this comparison weighed post-diagnosis survival among patients already diagnosed with stomach cancer, it does not directly measure how much screening reduced stomach cancer mortality across the entire population. The conclusions of the national statistical report also came from observational data comparing periods before and after screening. A 2014 review concluded that the extent to which the screening program contributed to the reduction in mortality needs further study, and how much of the drop in mortality should be attributed to screening remains an open question (PMID 25505712).

Whether to perform screening depends on guidance that varies according to local stomach cancer risk. A 2025 guideline by three European societies suggests endoscopy screening every 2 to 3 years in high-risk areas exceeding 20 cases per 100,000 population per year, every 5 years in intermediate areas with 10 to 20 cases where cost-effectiveness has been confirmed, and does not recommend it in areas with fewer than 10 cases (PMID 40112834). The 2025 guidelines from the American College of Gastroenterology (ACG) concluded that there is still insufficient evidence to decide whether or not to recommend endoscopy screening even for populations considered at high risk in the United States (PMID 40072510).

In Korea, where screening endoscopy is widespread, atrophic gastritis and intestinal-like changes are commonly diagnosed in the general population (PMID 40502844). The European guideline seen earlier notes that most people encountered in clinical practice fall into a mild group with no separately scheduled surveillance, but the abstracts gathered by this article do not state what proportion of people diagnosed in Korea fall into that group. Which group one belongs to is sorted out by looking at the extent of the changes and other risk factors together (PMID 40112834).

Where to Look Next

Among the things this article covered, the questions still open are when is the best time to perform an infection test, how precisely to screen out people at high risk, and what all those antibiotics do over the long term to other bacteria living in the body. The 2025 consensus statement also left these as tasks for further research (PMID 40912906).

The spot in the throat where the food path and the airway split before swallowed food touches the esophagus is in "Swallowing, Speech and Language — The Crossing Where the Food Path Meets the Airway". The story of how the meaning of a result changes depending on whether a disease is common or rare, even with the same test, is in "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability". "Better Numbers, Better Patients? — An Introduction to Surrogate Endpoints" helps read the result that eradication treatment reduced gastric cancer and gastric cancer deaths but did not change all-cause mortality.

Among the other parts of this series, "How Does Digestion Work? — A Tube Through the Body, and a Wall Only Small Pieces Can Cross" follows how food that has passed the stomach is broken down and absorbed in the small intestine, and "What Do Gut Microbes Do? — Guests Who Eat the Leftovers, Guests Who Hold the Room" follows the bacteria living at the end of the tube. Among the bleeding risk factors of the stomach and esophagus, a history of liver disease is where it connects with "How Do Fatty Liver, Hepatitis and Cirrhosis Connect? — Ground That Hardens as Scars Build Up, and the Stretch Where You Can Still Turn Back".

Source Papers

• "Global prevalence of, and risk factors for, gastro-oesophageal reflux symptoms: a meta-analysis." (2018) — PMID 28232473 — 102 studies and roughly 460,000 people, pooled prevalence of 13.3% based on heartburn or regurgitation at least once a week, large variation across countries, higher in those aged 50 and older, smokers, NSAID users, and individuals with obesity, though the associations are not large.
• "Helicobacter pylori infection." (2023) — PMID 37081005 — infects roughly half of the global population, varies by region and sanitation, acquired in childhood and persists for life if untreated, treatment combines strong acid suppressants and antibiotics, and a rapid rise in resistance to key antibiotics makes susceptibility testing, surveillance, and careful use necessary.
• "Gastric acid and digestive physiology." (2011) — PMID 21889024 — the stomach's main function is preparation for intestinal digestion and absorption, with acid at the center, helping wet food masses to aid digestion, while intact mucosal defense is essential to avoid ulcers.
• "Gastric acid secretion." (2016) — PMID 27607343 — gastric acid kills microbes, assists protein digestion, and helps absorb iron, calcium, and B12, while concerns about links between PPIs and kidney disease, dementia, and myocardial infarction have very low levels of evidence.
• "The Physiology of the Gastric Parietal Cell." (2020) — PMID 31670611 — parietal cells secrete gastric acid, regulated closely by the vagus nerve and hormones to balance digestion and prevent mucosal injury, and parietal cells also release growth factors involved in mucosal homeostasis and repair.
• "Pathophysiology of Gastroesophageal Reflux Disease." (2018) — PMID 29037470 — esophageal exposure to refluxate is the primary determinant of severity, exposure arises from weakened anti-reflux barriers and reduced esophageal clearance and buffering capacity, and impaired epithelial resistance or visceral hypersensitivity leads to symptoms and complications even at normal reflux volumes.
• "Pathophysiology of Gastroesophageal Reflux Disease." (2026) — PMID 40562014 — imbalance between defensive and offensive factors, esophagogastric junction dysfunction, transient lower esophageal sphincter relaxations, esophageal motility disorders, delayed gastric emptying, and thoracoabdominal pressure gradients, with acid and bile exposure and reduced clearance worsening injury, and neural regulation involved in symptom perception.
• "Gastro-oesophageal reflux disease." (2021) — PMID 34326345 — typical symptoms are heartburn and regurgitation, non-erosive reflux disease is the most common form, clinical diagnosis is often based on treatment response, and endoscopy and reflux monitoring are needed for accurate diagnosis.
• "Global Prevalence and Risk Factors of Gastro-oesophageal Reflux Disease (GORD): Systematic Review with Meta-analysis." (2020) — PMID 32242117 — 102 studies across 37 countries, global pooled prevalence of 13.98%, large variation across regions and countries (4.16% in China to 22.40% in Turkey), estimated at roughly 1.03 billion people.
• "Gastroesophageal Reflux Disease: A Review." (2020) — PMID 33351048 — obesity, smoking, and genetics increase risk, typical symptoms are often enough for diagnosis, endoscopy is indicated if alarm symptoms (dysphagia, weight loss, bleeding) or risk factors like older age, male sex, or obesity are present, PPIs are the most common treatment, long-term PPI harms are suggested by observational studies and should not guide clinical decisions before confirmation, and long-term treatment requires follow-up and re-evaluation.
• "AGA Clinical Practice Update on the Personalized Approach to the Evaluation and Management of GERD: Expert Review." (2022) — PMID 35123084 — roughly half of patients with suspected reflux gain no benefit from acid suppression, an expert review without graded evidence.
• "Italian guidelines for the diagnosis and management of gastro-esophageal reflux disease." (2025) — PMID 40450492 — Delphi consensus by 5 societies, supports symptom-based diagnosis, and recommends endoscopy if alarm symptoms are present or if there is no response to PPIs.
• "American Society for Gastrointestinal Endoscopy guideline on the diagnosis and management of GERD: summary and recommendations." (2025) — PMID 39692638 — suggests endoscopy for alarm symptoms, multiple risk factors for Barrett's esophagus, or a history of sleeve gastrectomy, and advises using PPIs at the lowest possible dose for the shortest duration.
• "Proton Pump Inhibitors (PPIs)-An Evidence-Based Review of Indications, Efficacy, Harms, and Deprescribing." (2025) — PMID 41010960 — associations between long-term PPIs and enteric infections, nutrient deficiencies, fractures, chronic kidney disease, and dementia come from observational studies, causality is not always established, and guidelines recommend periodic review and appropriate tapering.
• "Barrett Esophagus: A Review." (2022) — PMID 35972481 — roughly 5% in the US and roughly 1% globally, found in 2.3% to 8.3% of GERD patients and 1.2% to 5.6% of non-GERD individuals, progresses to esophageal adenocarcinoma at 0.2% to 0.5% per year, and surveillance endoscopy is recommended by guidelines despite a lack of randomized trials.
• "Diagnosis and Management of Barrett's Esophagus: An Updated ACG Guideline." (2022) — PMID 35354777 — Barrett's esophagus is a common condition associated with chronic GERD and the only known precursor lesion for esophageal adenocarcinoma.
• "An Overview of Helicobacter pylori Infection." (2021) — PMID 33765303 — pathogen research became active after Marshall and Warren's discovery in the early 1980s, increasing the risk of chronic gastritis, ulcers, and gastric cancer.
• "Pathogenicity and virulence of Helicobacter pylori: A paradigm of chronic infection." (2025) — PMID 39725863 — one of the most common infections in humans, most infected individuals are asymptomatic, it causes gastritis as well as ulcers and gastric cancer, and utilizes acid-defense enzymes, flagella, and adhesion proteins.
• "Screening and eradication of Helicobacter pylori for gastric cancer prevention: Taipei Global Consensus II." (2025) — PMID 40912906 — Delphi and GRADE involving 32 experts from 12 countries, Helicobacter is the main cause of gastric cancer, eradication reduces risk at all ages (greatest before precancerous changes), intra-familial transmission occurs, high-risk groups should be prioritized for testing, there is no increased risk of reflux or esophageal adenocarcinoma, and long-term effects on the microbiome and resistance need further study, concluding that eradication should be suggested for all infected adults.
• "Helicobacter pylori World Gastroenterology Organization Global Guideline." (2023) — PMID 36598803 — improving socioeconomic levels cuts transmission and reduces the burden most, requiring management tailored to local conditions.
• "[Clinical Practice Guideline for Gastritis in Korea]." (2024) — PMID 40502844 — gastritis is very common, emphasizing Helicobacter gastritis based on evidence of the Helicobacter-gastric cancer link and preventable nature through eradication, South Korea has the world's highest gastric cancer incidence, and screening endoscopy proliferation frequently diagnoses atrophic gastritis and intestinal metaplasia.
• "Helicobacter pylori-induced gastric inflammation and gastric cancer." (2014) — PMID 23981572 — classified as a Group 1 carcinogen by the International Agency for Research on Cancer, causing gastritis, ulcers, gastric cancer, and MALT lymphoma.
• "AGA Clinical Practice Update on the Diagnosis and Management of Atrophic Gastritis: Expert Review." (2021) — PMID 34454714 — atrophic gastritis means the loss of gastric glands amidst chronic inflammation driven mainly by Helicobacter or autoimmunity.
• "Gastritis: The clinico-pathological spectrum." (2021) — PMID 33785282 — long-standing gastritis leads to atrophy, which is a major factor driving gastric cancer.
• "Gastric Intestinal Metaplasia: Real Culprit or Innocent Bystander as a Precancerous Condition for Gastric Cancer?" (2023) — PMID 37652306 — the link between intestinal metaplasia and gastric cancer, with Helicobacter as the main cause of gastric cancer, and while Correa's stage model faces recent doubts, the author supports it, noting eradication is the most important prevention method yet has limited effect on already established intestinal metaplasia.
• "Helicobacter pylori Oncogenicity: Mechanism, Prevention, and Risk Factors." (2020) — PMID 32765194 — roughly 20% of infected individuals develop precancerous lesions, roughly 2% develop gastric cancer, and most are asymptomatic.
• "Management of epithelial precancerous conditions and early neoplasia of the stomach (MAPS III)." (2025) — PMID 40112834 — suggests endoscopic screening every 2 to 3 years in high-risk areas (>20 per 100,000 person-years), every 5 years if cost-effective in intermediate areas (10 to 20), does not suggest it in low-risk areas (<10), mild-to-moderate atrophy or intestinal metaplasia restricted to the antrum requires no surveillance if no other risk factors are present (most clinical cases), and extensive or advanced stages require surveillance every 3 years.
• "Helicobacter pylori eradication therapy to prevent gastric cancer: systematic review and meta-analysis." (2020) — PMID 32205420 — 7 RCTs of healthy individuals involving 8,323 people, gastric cancer RR 0.54 (NNT 72), gastric cancer mortality RR 0.61, no effect on overall mortality, with "moderate" certainty in East Asia.
• "Eradication Therapy to Prevent Gastric Cancer in Helicobacterpylori-Positive Individuals: Systematic Review and Meta-Analysis of Randomized Controlled Trials and Observational Studies." (2025) — PMID 39824392 — 8 RCTs of healthy individuals show an RR of 0.64, 5 RCTs on gastric cancer mortality show an RR of 0.78, and 11 observational studies show an RR of 0.56, with consistency across study designs.
• "Association Between Helicobacter pylori Eradication and Gastric Cancer Incidence: A Systematic Review and Meta-analysis." (2016) — PMID 26836587 — 24 studies involving 48,064 people, incidence rate ratio of 0.53, greater benefit with higher baseline gastric cancer incidence, but applicable across all levels.
• "Helicobacter pylori Infection and Eradication in Relation to Gastroesophageal Reflux Disease." (2025) — PMID 40662427 — 18 cohorts and 3 RCTs show increased GERD risk after eradication, author conclusion: infection is associated with reduced GERD, while eradication increases risk (Mendelian randomization using infection antibodies shows no association).
• "Peptic Ulcer Disease: A Review." (2024) — PMID 39466269 — 54,000 bleeding ulcer hospitalizations per year in the US, roughly 42% due to Helicobacter and roughly 36% due to NSAIDs, acid suppression achieves 80% to 100% healing within 4 weeks, eradication drops recurrence from 50% to 60% down to 0% to 2%, and NSAID cessation achieves 95% healing while dropping recurrence from 40% down to 9%.
• "Gastrointestinal Conditions: Peptic Ulcer Disease." (2024) — PMID 38767885 — main causes are Helicobacter and NSAIDs, cut by more than half over 20 years (presumed due to Helicobacter management, careful NSAID use, and PPI dissemination), and endoscopy is the diagnostic standard for older age or alarm symptoms.
• "Diagnosis and Treatment of Peptic Ulcer Disease." (2019) — PMID 30611829 — roughly two-thirds are asymptomatic, epigastric pain is the most common symptom, and most cases stem from Helicobacter, NSAIDs, or both.
• "Peptic ulcer disease." (2017) — PMID 28242110 — ulcers have declined due to reduced Helicobacter and widespread acid suppressants, making ulcers unrelated to Helicobacter or NSAIDs a diagnostic and therapeutic challenge.
• "Inflammation, acid and ulcers." (1994) — PMID 7502522 — chronic active type B gastritis results from Helicobacter infection and is a major factor in duodenal ulcers.
• "Peptic ulcer." (2023) — PMID 37365037 — mostly asymptomatic, sometimes first revealed by complications such as bleeding, perforation, or stricture, with diagnosis via upper endoscopy.
• "Evidence-based clinical practice guidelines for peptic ulcer disease 2020." (2021) — PMID 33620586 — Japanese Society of Gastroenterology guidelines, providing an algorithm for ulcer treatment and prevention when NSAIDs cannot be stopped.
• "Gastric cancer in asian american populations: a neglected health disparity." (2014) — PMID 25605140 — gastric cancer incidence in Korean men living in the US is more than 5 times that of non-Hispanic white men, and Japan and South Korea improved gastric cancer mortality after implementing early detection programs.
• "Prevention strategies for gastric cancer: a global perspective." (2014) — PMID 25505712 — South Korea and Japan are rare countries with endoscopy or radiography screening programs, and quantifying screening's contribution to mortality reduction needs further study.
• "[Helicobacter pylori]." (2025) — PMID 40924085 — first described as a pathogenic bacterium in 1983, with guidelines revised due to increasing resistance.
• "Gastroduodenal mucosal defense." (2014) — PMID 25229259 — research trends on mediators (such as mucins) involved in mucosal defense and healing.
• "Upper Gastrointestinal Bleeding." (2021) — PMID 33213769 — common cause of hospitalization in older adults, risk factors include older age, Helicobacter, drugs, smoking, and liver disease, and endoscopy serves as both a diagnostic and therapeutic tool.
• "Performance of the National Cancer Screening Program for Gastric Cancer in Korea." (2024) — PMID 40502340 — began in 1999, gastric cancer was South Korea's most frequent cancer until 2018, about 7.76 million screening endoscopies were performed in 2021, diagnosing 37.2% of the 29,361 gastric cancer cases that year, and the authors evaluate it as contributing to early detection and mortality reduction while discussing limitations.
• "Effect of gastric cancer screening on long-term survival of gastric cancer patients: results of Korean national cancer screening program." (2022) — PMID 35568752 — radiography or endoscopy every 2 years for those aged 40 and older, cohort of 46,701 patients diagnosed in 2008 to 2009, screened patients had a 53% lower risk of gastric cancer death (HR 0.47), with an even lower risk in the endoscopy group.
• "Epidemiology of Gastric Cancer in Korea: Trends in Incidence and Survival Based on Korea Central Cancer Registry Data (1999-2019)." (2022) — PMID 35938363 — age-standardized incidence dropped from 43.0 in 2011 to 29.6 in 2019, mortality dropped from 23.9 in 1999 to 6.7 in 2019, and 5-year relative survival rose from 55.7% (1999–2005) to 77.0% (2013–2019), with an increased proportion of localized stage diagnoses.
• "Descriptive Analysis of Gastric Cancer Mortality in Korea, 2000-2020." (2023) — PMID 36097804 — age-standardized mortality dropped from 29.0 to 7.9, with the reduction driven mainly by birth cohort effects (larger than period effects).
• "Cancer Statistics in Korea: Incidence, Mortality, Survival, and Prevalence in 2022." (2025) — PMID 40083085 — authors conclude that early detection and increased survival followed the introduction of the National Cancer Screening Program (2002), with the 5-year relative survival for gastric cancer increasing by 20.4 percentage points compared to 2001–2005.
• "ACG Clinical Guideline: Diagnosis and Management of Gastric Premalignant Conditions." (2025) — PMID 40072510 — insufficient evidence to recommend endoscopic screening for gastric cancer and precancerous conditions in US high-risk populations.