Tech entrepreneur and biohacker Bryan Johnson has revealed that he has been diagnosed with autoimmune gastritis, a chronic autoimmune disorder that damages the stomach lining and can lead to iron deficiency, vitamin B12 deficiency, and an increased risk of certain stomach cancers.
Johnson, 48, shared the diagnosis in a post on social media, describing the condition as one in which his "stomach is eating itself." He said he plans to continue researching ways to manage the disease, despite the fact that there is currently no cure.
The founder of the longevity-focused "Don't Die" movement said the diagnosis came after physicians investigated persistently low iron stores that failed to improve despite supplementation.
Low iron levels prompted further testing
According to Johnson, he had experienced low ferritin levels for years without developing anemia. Ferritin is a blood protein that stores iron, and low levels often indicate depleted iron reserves even before anemia develops.
He said his medical team initially ruled out gastrointestinal bleeding and colorectal cancer through a colonoscopy before conducting additional testing, including upper endoscopy, blood work, and stomach biopsies.
Johnson said laboratory tests revealed elevated anti-parietal cell antibodies, while biopsies showed early damage to the stomach lining consistent with autoimmune gastritis.
He also noted that he had been diagnosed with hypothyroidism at age 21 and has long taken thyroid hormone replacement medications, including levothyroxine and desiccated thyroid hormone. According to Johnson, physicians determined that his autoimmune thyroid disease and autoimmune gastritis were related and contributed to his chronic iron deficiency.
What is autoimmune gastritis?
Autoimmune gastritis (AIG), sometimes called autoimmune metaplastic atrophic gastritis, is a rare chronic condition in which the body's immune system mistakenly attacks parietal cells in the stomach. These cells produce stomach acid and intrinsic factor, a protein essential for vitamin B12 absorption.
Over time, destruction of these cells can lead to chronic inflammation, thinning of the stomach lining, and impaired absorption of nutrients.
According to the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), chronic gastritis may develop gradually over many years and often causes few or no symptoms in its early stages.
When symptoms do occur, they may include:
- Fatigue
- Abdominal discomfort
- Nausea
- Loss of appetite
- Unexplained weight loss
- Iron deficiency
- Vitamin B12 deficiency
Because the disease can progress silently, many patients are diagnosed only after laboratory tests reveal persistent nutritional deficiencies.
Autoimmune diseases often occur together
Autoimmune gastritis is frequently associated with other autoimmune disorders, particularly autoimmune thyroid disease.
The U.S. National Library of Medicine's MedlinePlus notes that people with one autoimmune condition are at higher risk of developing additional autoimmune diseases.
Johnson said this relationship complicated his treatment because low iron levels can interfere with thyroid hormone metabolism, while hypothyroidism may also affect the body's ability to utilize iron efficiently.
Medical experts have described this interaction as a cycle in which each condition may worsen the other if left untreated.
No cure exists, but treatment focuses on managing complications
There is currently no treatment that reverses autoimmune gastritis. Instead, management centers on correcting nutritional deficiencies, monitoring stomach health and screening for complications.
The Mayo Clinic says patients commonly require vitamin B12 replacement because intrinsic factor deficiency eventually prevents normal absorption of the vitamin. Iron supplementation or intravenous iron infusions may also be necessary if oral supplements fail to restore iron levels.
Johnson said he recently received a 1,000-milligram Monoferric iron infusion after oral iron supplements failed to normalize his ferritin levels.
Patients with autoimmune gastritis may also undergo periodic endoscopic surveillance because chronic inflammation and stomach atrophy have been associated with an increased risk of gastric adenocarcinoma and type 1 gastric neuroendocrine tumors, according to the National Cancer Institute.
Public disclosure highlights challenges of early diagnosis
Johnson's announcement adds to his long-running public documentation of health testing as part of his longevity initiative, in which he regularly shares laboratory results, imaging studies and experimental interventions intended to slow biological aging.
While autoimmune gastritis remains relatively uncommon, gastroenterologists emphasize that persistent iron deficiency—especially when unexplained or resistant to treatment—may warrant further evaluation for underlying gastrointestinal or autoimmune disorders.
Health experts also caution that people should not self-diagnose based on isolated laboratory findings. Persistent low ferritin, anemia, unexplained fatigue, or vitamin B12 deficiency should be evaluated by a healthcare professional, who may recommend blood tests, endoscopy or other diagnostic procedures depending on the patient's medical history and risk factors.
Although autoimmune gastritis cannot currently be cured, early recognition and ongoing monitoring can help reduce complications by addressing nutritional deficiencies and identifying changes in the stomach lining before more serious conditions develop.
