Autoimmune gastritis is a chronic inflammatory condition where the body's own antibodies attack acid-producing cells in the stomach, preventing proper nutrient absorption and increasing the risk of serious complications like anemia and stomach cancer. The disease affects an estimated 4% of people globally, yet it remains notoriously difficult to diagnose, often slipping past even experienced gastroenterologists.

What Happens Inside the Stomach When Autoimmune Gastritis Develops?

In autoimmune gastritis, the immune system mistakenly targets parietal cells, which produce stomach acid needed to break down food and absorb iron. Without adequate acid production, the body cannot properly absorb this essential mineral, leading to low ferritin levels, a blood protein that indicates how much iron the body is storing.

The condition creates a dangerous physiological feedback loop. When stomach acid drops too low, the stomach responds by secreting more gastrin, a hormone that normally signals acid production. But since the parietal cells that make acid are already destroyed, acid levels never rise. The stomach keeps producing gastrin in an attempt to fix the problem, and over time, excessive gastrin can trigger the growth of neuroendocrine tumors, a type of cancer that develops in hormone-producing cells.

What makes autoimmune gastritis particularly insidious is that it often remains silent for years. Symptoms frequently appear outside the digestive system entirely, manifesting as fatigue, weakness, or neurological issues rather than stomach pain or digestive complaints. This disconnect makes it easy for patients and doctors alike to miss the underlying cause.

Why Is Autoimmune Gastritis So Hard to Catch?

One major reason for delayed diagnosis is that early warning signs can be subtle and easily overlooked. Low ferritin levels are often an early indicator, but standard blood tests measuring hemoglobin and hematocrit, which detect anemia, may appear normal in the early stages. This creates a confusing picture where a patient has clear evidence of iron storage problems but no obvious anemia, making it easy to dismiss the concern.

A definitive diagnosis requires an upper endoscopy with biopsies, a procedure that allows doctors to examine the stomach lining directly and confirm the presence of antibodies attacking parietal cells. However, many gastroenterologists do not routinely perform biopsies on stomachs that appear normal during visual inspection, even when patients have a history of iron deficiency.

"I think gastroenterologists should really be sampling more 'normal'-appearing stomachs in patients with a history of iron deficiency that's been treated, because many of those patients will actually turn out to have autoimmune gastritis," said Toby Cornish, a gastrointestinal pathologist and professor at the Medical College of Wisconsin.

Toby Cornish, Gastrointestinal Pathologist and Professor, Medical College of Wisconsin

Experts recommend that anyone with low ferritin levels or iron deficiency anemia should receive an upper endoscopy and colonoscopy to screen not only for autoimmune gastritis but also for other causes of anemia, including colorectal cancer, colon polyps, and Helicobacter pylori stomach infections.

How to Recognize Early Signs and Seek Proper Testing

• Monitor ferritin levels: Regular blood tests showing consistently low ferritin, even when hemoglobin and hematocrit appear normal, warrant further investigation and discussion with your doctor about endoscopy screening.
• Report non-digestive symptoms: Unexplained fatigue, weakness, or neurological issues like tingling or numbness should be mentioned to your healthcare provider, as these can signal nutrient absorption problems rather than primary neurological disease.
• Request biopsies during endoscopy: If you have a history of iron deficiency and undergo upper endoscopy, ask your gastroenterologist whether biopsies of the stomach lining are being taken, even if the stomach appears visually normal.
• Discuss family history: People with autoimmune thyroid disease are more likely to develop autoimmune gastritis, so mention any autoimmune conditions in your medical history to your doctor.

What Are the Long-Term Health Risks?

The consequences of untreated autoimmune gastritis extend far beyond iron deficiency. Over time, the condition leads to vitamin B12 deficiency, which causes anemia and can trigger serious neurological complications if left unaddressed. Additionally, patients with autoimmune gastritis have a 13-fold increased risk of developing neuroendocrine tumors and a higher risk of adenocarcinomas, a serious form of stomach cancer.

The good news is that when neuroendocrine tumors are caught early through regular monitoring, the prognosis tends to be favorable, and they can often be treated endoscopically rather than requiring surgery.

What Treatment Options Are Currently Available?

Current standard medical care for autoimmune gastritis focuses on managing symptoms and preventing complications rather than curing the underlying condition. Patients typically receive iron supplementation, either taken orally or administered intravenously, to address nutritional deficiencies. They also require regular monitoring through endoscopy to screen for the development of stomach cancers.

Researchers are exploring experimental approaches, including CAR-T therapy, a personalized form of gene therapy that has shown promise in treating various autoimmune conditions. However, CAR-T therapy has not been extensively studied for autoimmune gastritis specifically, and it remains in early investigation stages.

"It's probably the best line of investigation for finding a cure in autoimmune gastritis. However, it's still very early," noted Toby Cornish.

Toby Cornish, Gastrointestinal Pathologist and Professor, Medical College of Wisconsin

The case of Bryan Johnson, a 48-year-old longevity entrepreneur who recently announced his autoimmune gastritis diagnosis, has brought unexpected attention to this overlooked condition. Despite spending millions of dollars on health optimization and describing himself as "the most biologically measured person ever," Johnson still missed his diagnosis until he underwent colonoscopy screening. His public disclosure may help raise awareness among both patients and healthcare providers about the importance of thorough diagnostic workup in cases of unexplained iron deficiency.

The key takeaway from experts is clear: no amount of health optimization can completely prevent autoimmune disease, and early detection through appropriate testing remains the most effective strategy for managing this condition and preventing serious complications.