What is celiac disease?

Wheat has been a basic staple of the human diet for around 10,000 years. Its success as a food source is largely due to its adaptability to growing conditions in temperate countries, its high yield and nutritional value, and because of gluten, a mixture of proteins contained within the wheat seed (and other related grains including barley and rye). Gluten forms a rubbery protein mass that gives dough its elasticity and helps it keep its shape, properties that make it ideally suited for processing into a wide variety of different foods including breads, pasta, and sweet treats like cakes and pastries.

Unfortunately, some people have an autoimmune disorder in which the immune system reacts to gluten, causing damage to the lining of the small intestine. This disorder is known as celiac disease.

Your digestive tract, or gut, is a tube that runs from your mouth to your anus. Digestion, or the breakdown of food, begins in your mouth. Once you have chewed and swallowed, the food travels to your stomach, and then into your small intestine, where most of the digestion and absorption of nutrients occurs. The small intestine has three distinct sections, called the duodenum, jejunum, and ileum that are uniquely designed for this function, and is where things may go wrong in celiac disease.

The duodenum receives partly digested food from the stomach, called acid chyme, as well as digestives enzymes from the pancreas that break down proteins and starch, and bile from the gall bladder that emulsifies fats. It produces an alkaline secretion that together with bicarbonate from the pancreas neutralizes the stomach acid that is in the chyme, allowing further digestion to take place.

The jejunum is the mid section of the small intestine. It contains circular folds that slow the passage of chyme and increase the surface area for absorption. The folds are covered in villi (from the latin word villos meaning “shaggy”), which are small finger-like projections. Each villus is covered in microvilli, which provide a vast surface area for absorption of fats and nutrients from chyme. Most of the nutrients produced from the food you eat are absorbed here.

The ileum is the final section of the small intestine. It also contains villi and microvilli that absorb any remaining nutrients, as well as vitamin B12 and bile acids.

The gut microflora: In addition to digesting the three major classes of nutrients (proteins, carbohydrates, and fats) and absorbing the majority of nutrients (amino acids, simple sugars, and lipids) present in your food, your small intestine is home to trillions of microbes that colonize the gut, known as the gut microflora. These mutually beneficial organisms not only help with digestion, but also stimulate your gut’s immune system to produce antibodies against potentially harmful organisms.

The gut immune system: your gut’s immune system is exposed to a multitude of disease-causing (pathogenic) organisms every day. Although its job is to eliminate them, it must do this without destroying the beneficial microbes in the gut microflora. Various immune system adaptations enable this, including that the intestinal lining itself is a strong physical barrier that protects against pathogens and prevents any undigested food components from stimulating an immune response. The result of the immune adaptations is that pathogenic organisms are quickly detected and efficiently eliminated, with any inflammation, a normal part of the immune response that occurs when tissues are injured by pathogens or any other cause, quickly subsiding. At the same time, the immune system is able to tolerate the beneficial organisms and ignore potential food allergens that could activate an immune response (most often proteins that are resistant to breakdown by the digestive enzymes in the digestive tract).

Gluten is a mixture of proteins, called prolamins that are found in cereal grains, especially wheat (gliadins and a glutenins), barley (hordeins), and rye (secalins). Gluten is somewhat resistant to digestion in the small intestine, so that when you eat food containing gluten, the digestive enzymes that normally break down proteins into their amino acids building blocks produce short strings of amino acids, called peptides, instead. For people with celiac disease, gluten peptides disrupt the lining of the small intestine and trigger an immune response that attracts inflammatory cells and increases the release of inflammatory chemicals. With continued exposure to gluten, the inflammatory response erodes the tiny villi (known as villous atrophy) of the intestinal wall, shortening and flattening them so they are unable to effectively absorb nutrients (malabsorption).

Genetic link: The inappropriate immune response to gluten is linked to your genetic makeup, particularly the human leukocyte antigen (HLA) gene family. These genes provide instructions for making proteins that help the immune system distinguish the body's own proteins from foreign proteins produced by pathogens or found in foods. The vast majority of people with celiac disease have either the HLA-DQ2 gene or the HLA-DQ8 gene; although, there are also many people who have these genes but do not have celiac disease. This means that having these genes is typically necessary but not sufficient to cause sensitivity to gluten. In addition to these genes a number of other genes have been associated with celiac diseases, although they do not seem to have as much influence on whether or not you will develop the disease.

The damage to the intestines caused by celiac disease can cause weight loss and malnourishment of organs and tissues, and may reduce growth and development of children. However, signs and symptoms can vary widely, from mild to severe, may or may not involve gastrointestinal symptoms, and for some people there may even be no symptoms at all. The classic symptoms of celiac disease are diarrhea, with or without symptoms caused by faulty absorption of nutrients by the intestines (malabsorption). However, only a minority of people have these classic symptoms, with many people experiencing few or atypical symptoms that may affect any organ from the the central nervous system to skin, joints, liver or teeth. To complicate matters further, many of the other signs and symptoms are nonspecific, which means they may occur in many disorders.

Intestinal symptoms: in addition to the classic symptom of diarrhea, intestinal damage may cause abdominal pain, bloating, mouth ulcers, and food intolerances; e.g, to lactose. Continued exposure to gluten causes chronic inflammation that may increase the risk of developing gastrointestinal cancers such as cancer of the intestine or esophagus, as well as ulcerative jejunitis (ulceration within the jejunum), or narrowing and obstruction of the intestine due to scarring.

Malabsorption-related symptoms: the damaged intestinal lining it less able to absorb a wide range of nutrients, minerals and fat-soluble vitamins including vitamins A, D, E, and K, and wide ranging symptoms may occur. For example: weight loss, or failure to thrive if you are a child may occur as a result of malabsorption of carbohydrates and fat; anemia may occur due to inadequate levels of iron, copper, or folic acid and vitamin B12; osteopenia or osteoporosis may result from a lack of calcium and vitamin D, while a zinc deficiency can cause stunted growth and mental slowness, hair loss, diarrhea, impotence, eye and skin conditions, and loss of appetite.

Miscellaneous symptoms: Various other signs and symptoms have been linked to celiac disease, although exactly how they are related to the immune reaction to gluten in the intestine is unclear. These include: neurological problems such as migraine headaches, depression, attention deficit hyperactivity disorder, and epilepsy; increased risk of infections and other autoimmune diseases such as Type 1 diabetes and rheumatoid arthritis; dermatitis herpetiformis, an itchy skin condition that may also be an autoimmune disease; delayed puberty; miscarriage; and symptoms associated with spleen and/or liver malfunction.

If you are genetically predisposed to celiac disease, it can develop at any age once you start eating foods containing gluten, although exactly why it happens, and why some people have mild symptoms and others have severe symptoms is unknown.

Genes: Because the risk of getting celiac disease increases if you have certain variants of genes that make proteins that control immune function, celiac disease tends to cluster in families, with first-degree family members (parents, siblings, children) having up to a 15% chance of getting it.${}^1$‍ Because having an autoimmune disease, such as Type 1 diabetes mellitus, thyroid disease, and primary biliary cirrhosis, makes you more likely to develop other autoimmune diseases, you also have an increased chance of getting celiac disease if you have any of these conditions.

Environmental triggers: The primary environmental trigger in celiac disease is gluten and gluten-related proteins that are present in wheat, barley and rye. This fits well with observations that introducing gluten into the diet of children who are genetically predisposed to celiac disease at 12 months of age rather than 6 months of age delayed onset of disease, but did not prevent it.${}^2$‍

The worldwide distribution of gluten-containing foods and the genes that predispose you to an immune reaction to gluten have made celiac disease the most common autoimmune disorder known, with around 1% of people affected in most parts of the world.${}^3$‍ That said, experts think this likely represents just the tip of the iceberg, as for each person who has been diagnosed there are many other people who are living with celiac disease but don’t know it. In addition, there is often a lag of many years before an immune reaction to gluten exposure develops. As such adult onset celiac disease is fairly common.

Its very straightforward, if you have celiac disease, you can prevent symptoms and further damage to your intestines by eating a strict gluten-free diet. However, it is important to have the cause of any symptoms properly diagnosed first.

Diagnosis: There are blood tests that can detect specific antibodies that indicate you have had an immune reaction to gluten. These tests can detect whether or not you have celiac disease even whether you have severe, mild or no symptoms at all. It is important not to go gluten-free prior to these tests as this may give a false negative result.

If your blood test is positive for celiac disease, your healthcare provider may recommend that you have an endoscopy, a non surgical procedure in which a flexible tube with a light and camera attached is introduced into your digestive tract so as to view the lining of your intestine. It is also possible to collect a tissue sample (biopsy) during this procedure to look for villous atrophy, and assess the extent of intestinal damage.

Treatment: There is no cure for celiac disease, and the only effective treatment is complete avoidance of gluten for life. A gluten-free diet requires avoiding all foods made from wheat, rye, and barley; for example, breads, cereals, pasta, crackers, cakes, pies, pastries, cookies, biscuits. Oats contain prolamins known as avenins, which are non toxic to the vast majority of people with celiac disease.${}^4$‍ However, it may be advisable to avoid them too, at least initially, due to the possibility that oats or oat-based foods are contaminated with other grains. If you have celiac disease try to stick to that gluten free diet, as the intestinal villi will recover completely within a year in two out of three cases; however, even a year is not long enough for people with more severe intestinal damage.${}^5$‍

For most people, there is no reason to avoid eating foods containing gluten. However, in addition to the gluten intolerance that affects people with celiac disease, another group of people report experiencing a non-celiac gluten sensitivity that causes similar symptoms. Notably, people with this condition do not test positive for celiac disease or for a wheat allergy. Gluten sensitivity causes a range of symptoms such as “foggy mind”, lack of energy or lethargy, gas, bloating, abdominal pain or cramps, diarrhea and sometimes constipation, but does not do the intestinal damage that occurs with celiac disease. The pathophysiology of this condition is currently poorly understood, and at this point, although it is referred to as gluten sensitivity it is not known whether gluten or another chemical component in wheat is responsible for the symptoms. There is no specific diagnostic test for gluten sensitivity. A diagnosis is made if you test negative for celiac disease or wheat allergy, and your symptoms resolve when you start a gluten-free diet, and start again when gluten is reintroduced. As with celiac disease, there is no cure for gluten sensitivity, and the only treatment is a gluten-free diet.