What Causes GERD?
GERD happens when the barrier between the stomach and esophagus weakens, or when the esophagus cannot clear refluxed contents fast enough. That is the conclusion of this 2021 review in the International Journal of Biological Sciences, which pulled together research on the “dynamic,” or mechanical, side of reflux disease. Normally the esophagus’s defenses and the damaging effect of refluxed stomach contents are in balance. GERD develops when that balance tips.
The review is a literature summary, not a new study. The authors searched PubMed, Web of Science and Embase up to August 2021 and organized what is known into two main failures: disruption of the anti-reflux barrier at the junction of the esophagus and stomach, and impaired esophageal clearance.
Dr. Kumar’s Take
This paper is a useful reminder that reflux is largely a plumbing problem. Acid is what burns, but the reason it ends up in the esophagus is mechanical: a valve that relaxes when it should not, a diaphragm that does not squeeze well, a hernia that moves the valve out of position, or an esophagus that does not push the acid back down. The authors are candid that the full picture is still not worked out, and that this gap is part of why treatment results are often unsatisfying. Knowing which mechanism is at fault matters, because a problem with the barrier and a problem with clearance are not fixed the same way.
The Anti-Reflux Barrier
A weak lower esophageal sphincter (LES). The LES is the most important part of the barrier. In healthy people its resting pressure is roughly 10 to 30 mmHg, which keeps stomach contents where they belong. Reflux occurs when that resting pressure is abnormally low and stomach pressure exceeds esophageal pressure.
Transient LES relaxations. These are brief relaxations of the sphincter that happen without swallowing and can last 10 to 45 seconds or more. The authors note they are now generally believed to be the main cause of reflux. They happen in healthy people too, but in healthy people the reflux is mostly gas, while in GERD it is more often acid. Only 40 to 50% of these relaxations come with acid reflux in healthy people, compared with 60 to 70% in people with GERD.
The crural diaphragm. Pressure at the junction of the esophagus and stomach comes from both the LES and the surrounding diaphragm muscle, which tightens with each breath. People with GERD have lower diaphragm tension at rest than healthy people.
Hiatal hernia. When part of the stomach slides up through the opening in the diaphragm, the LES and the diaphragm no longer line up, and the barrier weakens. Raised pressure inside the abdomen is the most common reason these hernias form, and GERD with a hiatal hernia is common in practice.
Esophageal Clearance
Once reflux happens, the esophagus normally clears it with saliva, gravity and coordinated waves of muscle contraction called peristalsis. When those waves are weak or uncoordinated, a pattern called ineffective esophageal motility, acid stays in contact with the lining longer and damage worsens. A test called multiple rapid swallowing, done during esophageal manometry, checks whether the esophagus has reserve strength to contract.
What Is Still Unknown
The authors list three open questions: exactly how hiatal hernia leads to GERD, whether weak esophageal contractions cause reflux or result from it, and how to measure esophageal clearance well during a reflux episode.
Practical Takeaways
- GERD is driven mainly by mechanical failures: a weak or inappropriately relaxing LES, a weak diaphragm, hiatal hernia, and poor esophageal clearance.
- Acid suppression lowers how damaging the refluxed fluid is, but it does not fix these mechanical problems.
- Risk factors the review lists include smoking, obesity, alcohol, NSAID use, psychosomatic conditions and genetics.
- If reflux persists despite treatment, esophageal testing such as manometry can show which mechanism is involved.
Related Studies and Research
- Specific Movement of Esophagus During Transient Lower Esophageal Sphincter Relaxation
- Hiatal Hernia, Lower Esophageal Sphincter and Their Combined Effect
- Global Prevalence and Risk Factors of Gastroesophageal Reflux Disease
- ACG Clinical Guideline: Guidelines for the Diagnosis and Management of Gastroesophageal Reflux Disease
- Episode 25: The Great GERD Mistake: How Medicine Made Heartburn Worse and How to Fix It
FAQs
What is the main cause of acid reflux according to this review?
Transient relaxations of the lower esophageal sphincter, brief openings of the valve that happen without swallowing, are now generally believed to be the main cause of reflux.
How does a hiatal hernia cause reflux?
A hiatal hernia moves the top of the stomach and the LES above the diaphragm, so the two structures that normally work together to block reflux no longer line up.
Why does weak esophageal movement matter?
Coordinated contractions push refluxed acid back into the stomach. When they are weak, acid stays in the esophagus longer and can cause more damage.
Can GERD lead to serious complications?
Yes. As the disease progresses, some people develop esophagitis, ulcers or narrowing of the esophagus, and in severe cases Barrett’s esophagus or esophageal cancer.
Bottom Line
This review frames GERD as a mechanical disease: a weakened anti-reflux barrier at the junction of the esophagus and stomach, plus an esophagus that clears refluxed contents poorly. The authors stress that the mechanisms are not fully understood, and that better understanding of them is the path to better treatment.
