Celiac disease is a disease of the small intestine. The small intestine is a 22 foot long tube that begins at the stomach and ends at the large intestine (colon). The first 10 inches (25cm) of the small intestine (the part that is attached to the stomach) is called the duodenum, the middle part is called the jejunum, and the last part (the part that is attached to the colon) is called the ileum. Food empties from the stomach into the small intestine where it is digested and absorbed into the body.
While food is being digested and absorbed, it is transported by the small intestine to the colon. What enters the colon is primarily undigested food. In celiac disease, there is an immunological (allergic) reaction within the inner lining of the small intestine to proteins (gluten) that are present in wheat, rye, barley and, to a lesser extent, in oats.
The immunological reaction causes inflammation that destroys the lining of the small intestine. This reduces the absorption of the dietary nutrients and can lead to symptoms and signs of nutritional, vitamin, and mineral deficiencies.
The other terms used forceliac disease include sprue, nontropical sprue, gluten enteropathy, and adult celiac disease. (Tropical sprue is another disease of the small intestine that occurs in tropical climates. Although tropical sprue may cause symptoms that are similar to celiac disease, the two diseases are not related.)
Celiac disease is common in European countries, particularly in Ireland, Italy, Sweden, and Austria. In Northern Ireland, for example, one in every 300 people has celiac disease. In Finland, the prevalence may be as high as one in every 100 persons. Celiac disease also occurs in North America where the prevalence has been estimated to be one in every 3000 people.
Unfortunately, most population studies underestimate the prevalence of celiac disease because many individuals who develop celiac disease have few or no symptoms until later in life. Moreover, a study suggests that the prevalence of celiac disease in the United States is similar to that in Europe.
The signs and symptoms of celiac disease vary depending on the degree of malabsorption, and ranges from no symptoms, few or mild signs and symptoms, to severe signs and symptoms.
There are two categories of signs and symptoms:
- signs and symptoms due to malabsorption,
- signs and symptoms due to malnutrition including vitamin and mineral deficiencies.
Signs and symptoms of malabsorption
The three major categories of dietary nutrients are carbohydrates, proteins, and fat. Absorption of all of these nutrients can be reduced in celiac disease; however, fat is the most commonly and severely affected nutrient. Most of the gastrointestinal symptoms and signs of celiac disease are due to the inadequate absorption of fat (fat malabsorption). Gastrointestinal symptoms of fat malabsorption include diarrhea, malodorous flatulence (foul smelling gas), abdominal bloating, and increased amounts of fat in the stool (steatorrhea).
The unabsorbed fat is broken down by intestinal bacteria into fatty acids, and these fatty acids promote secretion of water into the intestine, resulting in diarrhea. Fatty stools typically are large in volume, malodorous (foul smelling), greasy, light tan or light grey in color, and tend to float in the toilet bowl. Oil droplets (undigested fat) also may be seen floating on top of the water.
Loss of intestinal villi also causes malabsorption of carbohydrates, particularly the sugar lactose. Lactose is the primary sugar in milk. Lactose is made up of two smaller sugars, glucose and galactose. In order for lactose to be absorbed from the intestine and into the body, it must first be split into glucose and galactose.
The glucose and galactose can then be absorbed by the cells lining the small intestine. The enzyme that splits lactose into glucose and galactose is called lactase, and it is located on the surface of the small intestinal villi. In celiac disease the intestinal villi along with the lactase enzymes on their surface are destroyed, leading to the malabsorption of lactose.
The signs and symptoms of malabsorption of lactose are particularly prominent in individuals with celiac disease who have an underlying lactose intolerance, a genetically determined reduction in the activity of lactase. The symptoms of lactose malabsorption (diarrhea, excessive flatulence [passing gas], abdominal pain and abdominal bloating or distension) occur because unabsorbed lactose passes through the small intestine and into the colon. In the colon, the normal colony of bacteria contain lactase and are able to split the lactose, and utilize the resulting glucose and galactose for their own purposes.
Unfortunately, when they split the lactose into glucose and galactose, the bacteria also release gas (hydrogen and /or methane). A proportion of the gas is expelled and is responsible for the increased flatus (passing gas) that may occur in celiac disease. Increased gas mixed in the stool is responsible for the stools to float in the toilet bowl.
Not all of the lactose that reaches the colon is split and used by the colonic bacteria. The unsplit lactose that reaches the colon causes water to be drawn into the colon (by osmosis). This promotes diarrhea.
Signs and symptoms of malnutrition and vitamin or mineral deficiencies
Symptoms of malnutrition and vitamin or mineral deficiencies include: weight loss, fluid retention, anemia, osteoporosis, bruising easily, peripheral neuropathy (nerve damage), infertility, and muscle weakness.
Weight loss and fluid retention: Weight loss is the direct result of inadequate absorption of carbohydrates, proteins and fat. However, weight loss may not always occur because individuals with celiac disease often have an enormous appetite that compensates for the reduced absorption of nutrients.
Moreover, weight loss can be masked by fluid retention. Fluid retention occurs in advanced malnutrition because the reduced absorption of proteins results in low protein levels in the blood. Normal protein levels in the blood are necessary to keep fluid from leaking out of blood vessels and into the body's tissues. When blood protein levels fall as in celiac disease, fluid leaks into many tissues (edema) but particularly the ankles and feet, which swell due to the edema.
Lack of absorption of vitamin B12 and iron can lead to anemia.
Lack of absorption of vitamin D and calcium can lead to osteoporosis and bone fractures.
Lack of absorption of vitamin K can lead to diminished ability of blood to clot and hence to easy bruising or excessive bleeding.
Peripheral neuropathy (nerve damage):
Deficiencies of vitamins B12 and thiamine may contribute to nerve damage with symptoms of poor balance, muscle weakness, and numbness and tingling in the arms and legs.
Untreated celiac disease can lead to infertility in women, lack of menses (menstruation), spontaneous abortions and low birth weight infants.
Lack of absorption and low levels of potassiumand magnesium can lead to severe muscle weakness, muscle cramps, and numbness or tingling sensations in the arms and legs.
Abnormal liver tests: For unclear reasons, patients with celiac disease may have abnormal blood tests that suggest liver injury, specifically, elevated levels of aspartate amino transferase (AST) and/or leucine amino transferase (ALT). Occasionally, abnormalities of these tests may lead to a suspicion and subsequently a diagnosis of celiac disease.
The destruction of the inner lining of the small intestine in celiac disease is caused by an immunological (allergic) reaction to gluten in the diet that inflames and destroys the inner lining of the small intestine. There is evidence that this reaction is partially genetic and partially inherited.
Thus, approximately 10% of the first-degree relatives (parents, siblings or children) of individuals with celiac disease also will have celiac disease. In addition, in approximately 30% of fraternal twins and 70% of identical twins, both twins will have celiac disease. Finally, certain genes have been found to be more common in individuals with celiac disease than in those without celiac disease.
Gluten is a family of proteins present in wheat. Some of the proteins that make up gluten (the ones that are dissolved by alcohol) are called gliadin. It is the gliadin in gluten that causes the immunological reaction in celiac disease. The mechanism whereby gliadin becomes toxic (damaging) is not clear; however, much scientific study is being done, and we are beginning to understand the mechanism.
Proteins, including gliadin, are long chains of amino acids-up to several hundred-attached to each other. Normally during digestion, the digestive enzymes within the small intestine break-up proteins into single amino acids and smaller chains of amino acids.
This is necessary because the intestine can only absorb single amino acids or, at most, chains of 3-4 amino acids. Single amino acids and chains of several amino acids do not cause problems for the intestine. It appears, however, that gliadin is not completely broken-up by intestinal enzymes. Several longer chains of amino acids remain intact.
Somehow these larger chains enter the cells lining the intestine, perhaps because the cells are abnormally permeable (leaky) to longer chains of amino acids. Some of these longer chains are toxic (damaging) to the intestinal cells.
One of the longer chains attaches to an enzyme (tissue transglutaminase) inside the cells. In individuals with celiac disease, the complex of the longer chain of amino acids and tissue transglutaminase sets off an immune reaction that attacks the complex and at the same time damages the intestinal cells.
Barley and rye contain gliadin-like proteins and can cause celiac disease in genetically-predisposed individuals. Oats also contain gliadin-like proteins, but unlike barley and rye, the gliadin-like proteins in oats cause only a mild inflammation and that too in only a few individuals who are predisposed to develop celiac disease. Rice and corn do not cause celiac disease because they do not contain gliadin-like proteins.
There is no cure for celiac disease. The treatment of celiac disease is a gluten free diet. Celiac disease patients vary in their tolerance of gluten; some patients can ingest small amounts of gluten without developing symptoms while others experience massive diarrhea with only minute amounts of gluten. The standard treatment of disease patients calls for complete avoidance of gluten for life.
The principles of a gluten free diet include:
- Avoid all foods made from wheat, rye, and barley. Examples are breads, cereals, pasta, crackers, cakes, pies, cookies, and gravies.
- Avoid oats. Some patients with celiac disease can tolerate oats in the diet. But long-term safety of oats in celiac disease patients is unknown. Also some oat preparations can be contaminated with wheat. Thus, it is probably best to avoid oats at least during the initial treatment with a gluten free diet. Once disease remission is achieved with a strict gluten free diet, small quantities of oats can be reintroduced into the diet under medical supervision.
- Pay attention to processed foods that may contain gluten. Wheat flour is a common ingredient in many processed foods.
Examples of foods that may contain gluten, to name only a few, include:
- canned soups,
- salad dressings,
- ice cream,
- candy bars,
- instant coffee,
- luncheon meats,
- processed and canned meats,
- Beware of tablets, capsules, and vitamin preparations that contain gluten. Wheat starch is commonly employed as a binding agent in tablets and capsules. Gluten also can be found in many vitamin products, and cosmetic products such as lipstick.
- Avoid beer.
- It is all right to drink wine, brandy, whiskey and other non-wheat or barley alcohol (in moderation!).
- Avoid milk and other dairy products that contain lactose. Untreated patients with celiac disease often are lactose intolerant. With successful treatment, dairy products can be reintroduced slowly into the diet later.
- It is alright to consume fish, fresh meats, rice, corn, soybean, potato, poultry, fruits, vegetables, and dairy products (for patients who are not lactose intolerant).
- Consult dietitians and national celiac disease societies for lists of gluten free foods. Read the food and product labels before buying or consuming any product. This is necessary because a manufacturer may change a product's ingredients at any time. A product that was gluten-free in the past may now contain gluten. Even branded products may be gluten free in one country but contain gluten in another country. If one is not certain after reading the labels, call the manufacturer.
- Because patients with severe malabsorption can develop vitamin and mineral deficiencies, vitamin and mineral supplements are important. All patients should take a multivitamin daily. Patients with iron deficiency anemia should be treated with iron. Patients with anemia due to folate or B12 deficiency should be treated with folic acid and B12. Patients with an abnormal ProTime should be treated with vitamin K. Patients with low blood calcium levels or with osteoporosis should be treated with calcium and vitamin D supplements.