Celiac disease is an autoimmune condition where eating gluten triggers your immune system to attack the lining of your small intestine. This damages the tiny finger-like projections (called villi) that absorb nutrients from food, leading to malnutrition and a wide range of symptoms that extend far beyond the gut. About 1.4% of the global population has it, though many remain undiagnosed.
How Gluten Triggers an Immune Attack
When someone with celiac disease eats gluten, a protein found in wheat, rye, and barley, their immune system treats it as a threat. The response has two parts. First, specialized immune cells flood into the intestinal lining and begin attacking the tissue directly. Second, the body produces antibodies that target an enzyme called tissue transglutaminase, which is found throughout your own intestinal wall. This means celiac disease isn’t just an immune reaction to gluten. It’s an autoimmune reaction where the body turns on itself.
Over time, this repeated assault flattens the villi that line the small intestine. Healthy villi look like a shag carpet under a microscope, maximizing the surface area available to pull nutrients from food. In celiac disease, they gradually wear down to something closer to a tile floor. The crypts between them also deepen and multiply as the body tries to regenerate damaged tissue. This structural damage is what drives most of the disease’s consequences.
Digestive Symptoms
The classic symptoms are what you’d expect from intestinal damage: diarrhea, bloating, abdominal pain, and gas. Some people experience constipation instead. Because the damaged intestine can’t break down lactose efficiently, many people with celiac disease also develop temporary lactose intolerance, which adds another layer of digestive discomfort until the gut heals.
But here’s what surprises many people: digestive symptoms aren’t universal. Some adults with celiac disease have minimal gut complaints, which is one reason the condition goes undiagnosed for years. The damage is still happening beneath the surface, even without obvious stomach problems.
Nutrient Deficiencies at Diagnosis
Flattened villi can’t absorb nutrients properly, so deficiencies are extremely common by the time someone is diagnosed. A Mayo Clinic study found that zinc deficiency was the most frequent, affecting 59.4% of patients at diagnosis. Iron, vitamin D, copper, vitamin B12, and folate deficiencies were also widespread.
These aren’t minor shortfalls. Iron deficiency causes anemia, which is actually the second most common way celiac disease shows up in adults, accounting for about 15% of initial presentations. The fatigue, weakness, and shortness of breath from anemia can be severe enough to prompt medical evaluation on their own. In fact, guidelines in both the UK and US recommend that anyone with unexplained iron-deficiency anemia be tested for celiac disease, since endoscopic studies have found celiac disease in up to 8.7% of anemia patients.
Vitamin D and copper deficiencies contribute to bone thinning and neurological problems, respectively. Folate and B12 shortfalls can cause their own forms of anemia and nerve dysfunction. Many of these deficiencies resolve on a gluten-free diet as the intestine heals, but some, particularly severe bone loss, may not fully reverse.
Effects Beyond the Gut
Celiac disease reaches well beyond the digestive tract. The same immune process that damages the intestine can affect the skin, brain, bones, and reproductive system.
Skin
Dermatitis herpetiformis is a painful, intensely itchy rash that develops on the elbows, knees, buttocks, and lower back. It happens because the antibodies produced during the intestinal immune reaction travel through the bloodstream and bind to a related enzyme in the skin, triggering inflammation there. It’s essentially celiac disease expressing itself through the skin rather than the gut, and it responds to the same gluten-free diet.
Nervous System
Gluten ataxia is one of the most common neurological effects, responsible for roughly half of all neurological presentations of celiac disease. It causes problems with balance, coordination, walking, and sometimes eye movements. The mechanism involves antibodies that cross-react with cells in the cerebellum, the brain region that controls coordinated movement. Nerve damage in the hands and feet (peripheral neuropathy) is another possibility.
Bones and Fertility
Chronic malabsorption of calcium and vitamin D leads to progressive bone weakening. Left untreated long enough, this can become severe osteoporosis, and advanced bone loss may be irreversible even after starting a gluten-free diet. Celiac disease also contributes to infertility in both men and women, another complication that may not be fully reversible if the disease goes unmanaged for years.
Linked Autoimmune Conditions
People with celiac disease are significantly more likely to develop other autoimmune disorders. One study found that 35.3% of celiac patients had at least one additional autoimmune condition, compared to 15.2% of the general population.
Hashimoto’s thyroiditis (autoimmune thyroid disease) is the most common overlap, affecting about 24% of celiac patients, roughly 2.5 times the rate seen in the general population. Type 1 diabetes, psoriasis, Sjögren syndrome, inflammatory bowel disease, and autoimmune arthritis also occur at elevated rates. A large Israeli study of over two million adolescents found celiac disease was associated with a 5.5-fold increased risk of type 1 diabetes and a 3.8-fold increased risk of inflammatory bowel disease.
How It’s Diagnosed
Diagnosis typically starts with a blood test that looks for specific antibodies. The most common screening test checks for antibodies targeting tissue transglutaminase. If that test is positive, a small intestinal biopsy confirms the diagnosis by showing the characteristic flattening of villi and increased immune cells in the tissue. You need to be actively eating gluten for both tests to be accurate, so going gluten-free before testing can produce a false negative.
Genetic testing can also play a role. Nearly all celiac patients carry one or both of two specific gene variants (HLA-DQ2 and HLA-DQ8). Having the genes doesn’t mean you’ll develop celiac disease, but not having them essentially rules it out. This makes genetic testing most useful for excluding the diagnosis in uncertain cases.
Treatment: A Strict Gluten-Free Diet
The only established treatment for celiac disease is a lifelong, strictly gluten-free diet. This means completely eliminating wheat, rye, and barley from your food. In the US, foods labeled “gluten-free” must contain less than 20 parts per million of gluten, which is the lowest level that can be reliably detected with current testing methods. Most people with celiac disease tolerate foods at or below that threshold.
Once gluten is removed, the intestinal lining begins to heal. Villi gradually regrow, nutrient absorption improves, and many symptoms resolve within weeks to months. Antibody levels drop back toward normal. For most people, a well-maintained gluten-free diet is enough to put the disease into remission and prevent complications.
The challenge is that even small, unintentional gluten exposures can reactivate the immune response and restart intestinal damage. Cross-contamination in shared kitchens, hidden gluten in sauces or processed foods, and dining out all pose ongoing risks. Learning to navigate these situations is a major part of living with celiac disease.
When the Diet Doesn’t Work
In roughly 1% of celiac patients, intestinal damage persists despite strict gluten avoidance. This is called refractory celiac disease, and it comes in two forms. Type 1 involves ongoing villous damage but a normal immune cell population, and it generally responds to additional treatment. Type 2 involves abnormal, clonal immune cells expanding in the gut and potentially other organs. This form carries a poorer prognosis and an increased risk of a rare intestinal lymphoma. Refractory celiac disease is uncommon, but it’s why ongoing monitoring matters even after diagnosis.