Autoimmune Gastritis: Signs, Causes & What to Know

Longevity guru Bryan Johnson recently shared his autoimmune gastritis diagnosis, and it made headlines. His story is a wake-up call for anyone with low iron that just won’t improve. Autoimmune gastritis is a condition where your immune system attacks your stomach lining. It can be silent for years. But there’s a key clue: low ferritin (stored iron) that stays low even after taking supplements. In this article, we’ll explain what autoimmune gastritis is, how it relates to iron deficiency, and what you can do about it.

What Is Autoimmune Gastritis?

Let’s break it down. In autoimmune gastritis, your immune system attacks certain cells in your stomach. These cells, called parietal cells, make stomach acid and a protein needed to absorb B12. When they get damaged, acid levels drop. That makes it hard for your body to release iron from food. B12 absorption also suffers.

About 0.5% to 2% of people in the U.S. have this condition. It’s not the same as H. pylori gastritis, which is a bacterial infection treatable with antibiotics. Autoimmune gastritis isn’t caused by an infection, and it can’t be reversed. But it can be managed.

The Hidden Link Between Autoimmune Gastritis and Low Iron

Here’s the part that matters: autoimmune gastritis is often missed as a cause of iron deficiency. “It can absolutely be missed, even in someone who is getting very thorough medical care,” says Dr. Felice Schnoll-Sussman, a gastroenterologist at Weill Cornell Medicine. She notes the condition is “often quiet for a long time.” Symptoms like fatigue, poor focus, low energy, and mild indigestion are easy to blame on stress or lack of sleep.

The key clue is a low ferritin level that stays low even after you take iron pills. You may not have anemia yet. You may not feel sick. But your iron stores remain low because your stomach can’t absorb it properly. That’s the signal to dig deeper.

Subtle Symptoms You Should Know

Most people with early autoimmune gastritis have no symptoms at all. That’s why it’s called silent. But as the stomach lining gets thinner, symptoms can show up. Fatigue is the most common, and it’s easy to brush off. “The overwhelming majority of these cases are asymptomatic,” says Dr. Ashkan Farhadi, a gastroenterologist at MemorialCare Orange Coast Medical Center.

Other signs include heartburn, reflux, feeling full after a small meal, or bloating. Over time, iron deficiency anemia may develop, causing pale skin, weakness, and shortness of breath. B12 deficiency can cause nerve problems like numbness, tingling, or memory trouble. But remember: you can have autoimmune gastritis for years without obvious symptoms. That’s why stubborn low iron is such a big clue.

How Is Autoimmune Gastritis Diagnosed?

If you and your doctor suspect autoimmune gastritis, the next step is blood tests. These can check for antibodies that attack stomach cells. Your doctor will also check your iron, ferritin, B12, and look for anemia.

The best way to confirm it is an upper endoscopy with biopsies. A thin tube with a camera goes into your stomach. The doctor takes tiny samples of the lining to look for thinning and cell loss. That’s how Bryan Johnson finally got his answer after years of low ferritin.

Dr. Schnoll-Sussman advises: “In patients with unexplained iron deficiency, whether or not anemia is already present, autoimmune atrophic gastritis should be considered as a possible cause.”

What to Expect: Treatment and Monitoring

There’s no cure for autoimmune gastritis. No pill can stop the immune attack on your stomach. But that doesn’t mean nothing works. Treatment focuses on managing the results and preventing problems.

The main approach is replacing the nutrients you can’t absorb. That might mean high-dose iron (sometimes through an IV if pills don’t work), vitamin B12 shots or high-dose oral B12, and sometimes other vitamins like D or calcium if levels drop.

“We are going after the consequences and preventing complications,” says Dr. Farhadi. “Our role is damage control.”

Because autoimmune gastritis raises the risk of stomach cancer — about 0.12% of patients develop it each year — doctors often recommend a follow-up endoscopy every 2 to 5 years. This catches any precancerous changes early.

On the lifestyle side, managing stress can help. Dr. Farhadi notes that stress affects the gut — a topic covered in depth in our guide on how fiber and inflammation are connected. While it won’t cure the condition, eating well, exercising, and sleeping enough can support your overall health.

FAQ About Autoimmune Gastritis

The Bottom Line

If your iron stays low no matter what, you are not alone. Autoimmune gastritis is more common than many think, and it’s easy to overlook. The good news is that once it’s found, it can be managed. You may need iron through an IV or B12 shots, but you can feel much better.

The key takeaway is simple: listen to your body and your lab results. If your iron is low and supplements don’t fix it, or you have tiredness with mild stomach upset, bring up autoimmune gastritis with your doctor. You don’t need a celebrity story to get the right tests — just the right questions.