What causes constipation?
To understand constipation, it helps to know how the colon (large intestine) works. As food moves through the colon, it absorbs water while forming waste products, or stool. Muscle contractions in the colon push the stool toward the rectum. By the time stool reaches the rectum, it is solid because most of the water has been absorbed.
The hard and dry stools of constipation occur when the colon absorbs too much water or if the colon's muscle contractions are slow or sluggish, causing the stool to move through the colon too slowly. Common causes of constipation are
- not enough fiber in the diet
- not enough liquids
- lack of exercise
- irritable bowel syndrome
- changes in life or routine such as pregnancy, older age, and travel
- abuse of laxatives
- ignoring the urge to have a bowel movement
- specific diseases such as stroke (by far the most common)
- problems with the colon and rectum
- problems with intestinal function (chronic idiopathic constipation)
Not Enough Fiber in the Diet
The most common cause of constipation is a diet low in fiber found in vegetables, fruits, and whole grains and high in fats found in cheese, eggs, and meats. People who eat plenty of high-fiber foods are less likely to become constipated.
Fiber—both soluble and insoluble—is the part of fruits, vegetables, and grains that the body cannot digest. Soluble fiber dissolves easily in water and takes on a soft, gel-like texture in the intestines. Insoluble fiber passes through the intestines almost unchanged. The bulk and soft texture of fiber help prevent hard, dry stools that are difficult to pass.
According to the National Center for Health Statistics, Americans eat an average of 5 to 14 grams of fiber daily,* short of the 20 to 35 grams recommended by the American Dietetic Association. Both children and adults eat too many refined and processed foods from which the natural fiber has been removed.
A low-fiber diet also plays a key role in constipation among older adults, who may lose interest in eating and choose convenience foods low in fiber. In addition, difficulties with chewing or swallowing may force older people to eat soft foods that are processed and low in fiber.
*National Center for Health Statistics. Dietary Intake of Macronutrients, Micronutrients, and Other Dietary Constituents: United States, 1988–94. Vital and Health Statistics, Series 11, number 245. July 2002.
Not Enough Liquids
Liquids like water and juice add fluid to the colon and bulk to stools, making bowel movements softer and easier to pass. People who have problems with constipation should drink enough of these liquids every day, about eight 8-ounce glasses. Liquids that contain caffeine, like coffee and cola drinks, and alcohol have a dehydrating effect.
Lack of Exercise
Lack of exercise can lead to constipation, although doctors do not know precisely why. For example, constipation often occurs after an accident or during an illness when one must stay in bed and cannot exercise.
Some medications can cause constipation. They include
- pain medications (especially narcotics)
- antacids that contain aluminum and calcium
- blood pressure medications (calcium channel blockers)
- antiparkinson drugs
- iron supplements
Irritable Bowel Syndrome (IBS)
Some people with IBS, also known as spastic colon, have spasms in the colon that affect bowel movements. Constipation and diarrhea often alternate, and abdominal cramping, gassiness, and bloating are other common complaints. Although IBS can produce lifelong symptoms, it is not a life-threatening condition. It often worsens with stress, but there is no specific cause or anything unusual that the doctor can see in the colon.
Changes in Life or Routine
During pregnancy, women may be constipated because of hormonal changes or because the heavy uterus compresses the intestine. Aging may also affect bowel regularity because a slower metabolism results in less intestinal activity and muscle tone. In addition, people often become constipated when traveling because their normal diet and daily routines are disrupted.
Abuse of Laxatives
Myths about constipation have led to a serious abuse of laxatives. This is common among people who are preoccupied with having a daily bowel movement.
Laxatives usually are not necessary and can be habit-forming. The colon begins to rely on laxatives to bring on bowel movements. Over time, laxatives can damage nerve cells in the colon and interfere with the colon's natural ability to contract. For the same reason, regular use of enemas can also lead to a loss of normal bowel function.
Ignoring the Urge to Have a Bowel Movement
People who ignore the urge to have a bowel movement may eventually stop feeling the urge, which can lead to constipation. Some people delay having a bowel movement because they do not want to use toilets outside the home. Others ignore the urge because of emotional stress or because they are too busy. Children may postpone having a bowel movement because of stressful toilet training or because they do not want to interrupt their play.
Diseases that cause constipation include neurological disorders, metabolic and endocrine disorders, and systemic conditions that affect organ systems. These disorders can slow the movement of stool through the colon, rectum, or anus.
Several kinds of diseases can cause constipation:
Metabolic and endocrine conditions
- multiple sclerosis
- Parkinson's disease
- chronic idiopathic intestinal pseudo-obstruction
- spinal cord injuries
- underactive or overactive thyroid gland
Problems with the Colon and Rectum
Intestinal obstruction, scar tissue (adhesions), diverticulosis, tumors, colorectal stricture, Hirschsprung's disease, or cancer can compress, squeeze, or narrow the intestine and rectum and cause constipation.
Problems with Intestinal Function (Chronic Idiopathic Constipation)
Some people have chronic constipation that does not respond to standard treatment. This rare condition, known as idiopathic (of unknown origin) chronic constipation may be related to problems with intestinal function such as problems with hormonal control or with nerves and muscles in the colon, rectum, or anus. Functional constipation occurs in both children and adults and is most common in women.
Colonic inertia and delayed transit are two types of functional constipation caused by decreased muscle activity in the colon. These syndromes may affect the entire colon or may be confined to the lower or sigmoid colon.
Functional constipation that stems from abnormalities in the structure of the anus and rectum is known as anorectal dysfunction, or anismus. These abnormalities result in an inability to relax the rectal and anal muscles that allow stool to exit.