Constipation

Constipation is a condition of infrequent or uncomfortable bowel movements.

People often disagree over what is meant by "infrequent." Many people believe they are constipated if they do not have several bowel movements every day. However, even daily bowel movements are not normal for everyone. Having less frequent bowel movements does not necessarily indicate a problem unless the frequency has decreased noticeably. For many older people, constipation means straining with bowel movements; passage of small, hard stools; or a sense that they have not emptied their rectum completely.

Constipation sometimes develops suddenly and lasts briefly. Among older people, however, constipation more often begins gradually and persists for months or years. Fortunately, constipation usually responds well to treatment.

Causes

Constipation most commonly occurs when the waste (stool) that forms after food is digested moves too slowly (slow transit) as it passes through the digestive tract. Dehydration, changes in diet and activity, and certain drugs are frequently to blame for slow transit of stool. When stool moves slowly, too much water is absorbed from the stool, and it becomes hard and dry. Gradual enlargement of the rectum and impaired coordination of the pelvic and anal muscles sometimes contribute to or cause constipation. Sometimes a combination of these processes occurs. A fourth cause, bowel obstruction, is serious but very uncommon.

Slow transit of stool: When transit of stool slows, more water is pulled from the stool, resulting in hard and dry stools that are difficult to pass.

Dehydration slows transit, because the body's response to dehydration is to remove additional water from stool in an effort to conserve its supply of water. Similarly, changes in diet, particularly eating foods low in fiber, can slow transit, because fiber helps hold water in the stool and increases its bulk. Stool that contains less water moves more slowly through the digestive tract.

The decline in physical activity that often accompanies aging may slow transit, because physical activity stimulates the intestines to move stool along.

Many drugs slow transit of stool through the large intestine. These include iron; opioids; certain drugs taken for high blood pressure or coronary artery disease, such as calcium channel blockers; drugs with anticholinergic effects (for example, certain antihistamines, sedatives, and antidepressants); antacids that contain calcium or aluminum hydroxide; and some drugs used to relieve nausea (serotonin antagonists).

Certain disorders can slow intestinal transit, including an underactive thyroid gland (hypothyroidism), high blood calcium levels (hypercalcemia), and Parkinson's disease. Diabetes can damage nerves that normally help control intestinal transit. Nerve or spinal cord injury may also slow transit. Abdominal surgery may slow transit as well, because bands of fibrous tissues (adhesions) that can gradually form after surgery can slow or even block (obstruct) movement of stool through the digestive tract. Noncancerous (benign) and cancerous (malignant) tumors can obstruct the digestive tract. Chronic pain and certain mental health disorders, especially depression, can also slow transit by interfering with the digestive tract's ability to move stool.

Rectal enlargement: In some older people, the rectum enlarges for no obvious reason. As the rectum enlarges, it becomes less able to sense accumulating stool, and its contractions weaken. As rectal contractions weaken, stool is not expelled as effectively. Constipation results as more and more stool accumulates. This accumulating stool may be putty-like or may harden. Impaction results when the rectum can no longer empty the stool that accumulates. Once enlargement and weakened contractions have begun, added fiber (the indigestible part of food) in the diet or fiber taken in a laxative preparation can worsen constipation and promote impaction. Delaying bowel movements habitually can also contribute to enlargement of the rectum and impairment of rectal contractions.

Impaired coordination of pelvic and anal muscles: A normal bowel movement involves relaxation of the pelvic support muscles (the muscles that support the bladder, uterus, and rectum) and of the circular band of muscle that keeps the anus closed (anal sphincter). Contraction and relaxation of pelvic support muscles and anal muscles are coordinated by the brain, the spinal cord, and certain nerves. If coordination of the pelvic and anal muscles is impaired, the person may sense the need to have a bowel movement, but the pelvic support muscles and the anal sphincter do not relax. This faulty coordination leads to constipation.

Symptoms

In addition to infrequent bowel movements, a person with constipation may describe having to strain to have a bowel movement. Hemorrhoids can develop from increased pressure created by straining. Some people report passing stools that are hard or small and feeling as if the rectum has not been completely emptied after a bowel movement. Constipation involving impaction of stool in the rectum may be accompanied by loss of control of bowel movements or by leakage and soiling (fecal incontinence).

When constipation is caused by worsening obstruction, the person may first have a decreased appetite, followed by nausea and vomiting.

Diagnosis

A doctor usually relies on the person's account of constipation when making a diagnosis. But the doctor also examines the rectum with a gloved finger and, if stool is present, determines the amount and consistency. The person's symptoms and an examination are often all that are needed to confirm a diagnosis of constipation and to determine the likely cause.

When the cause remains unclear, blood tests may be done. The doctor may also recommend an examination with a flexible viewing tube, either of just the lower part (rectum and sigmoid colon) of the large intestine (sigmoidoscopy) or of the entire large intestine (colonoscopy). This examination is important if the constipation developed suddenly or if it is worsening noticeably.

Occasionally, other tests are needed to determine the cause. A plain x-ray may show evidence of bowel obstruction or suggest another cause. Another test involves swallowing several capsules containing tiny rings that can be seen on x-rays. An x-ray is taken several days later. If more than 20% of the rings remain in the digestive tract 5 days after they have been swallowed, transit time through the intestine is slow. Another type of test involves use of x-rays after a dye (barium) has been instilled into the rectum. X-rays are taken while the person tries to move his bowels and pass the barium.

Treatment

Constipation with impaction: When stool is impacted, tap water enemas are commonly used. Although people receiving an enema can be placed in a variety of positions, usually they are positioned so that they are lying on their left side, with knees flexed and drawn up toward the chest. About 5 to 10 ounces of water at body temperature are gently instilled into the rectum and sigmoid colon. The water is instilled through a tube with a bulb that is squeezed to draw the water up and then squeezed again to push the water out. When the water is expelled from the rectum, the impacted stool is expelled with it. Nonprescription prepackaged enemas containing sodium biphosphate can be used in place of tap water but offer no advantages.

If enemas fail to work, a health care practitioner may need to remove the stool manually using a gloved finger. The person is then sometimes asked to drink a solution containing dissolved salts (electrolytes) and polyethylene glycol, which cleanses the digestive tract.

After the impaction has been removed, the person may be told to add fiber to the diet or to use laxatives to prevent constipation. Small amounts of polyethylene glycol-containing solution may be given daily as well. Laxatives may be used every 2 to 3 days to stimulate bowel contractions if a bowel movement does not occur spontaneously.

Constipation without impaction: If the stool is not impacted, several options are available for treating constipation.

Diet and physical activity are often the most important treatment considerations. Increasing the intake of fluids and fiber is often the first step. Vegetables, fruits (especially prunes), whole-grain breads, and high-fiber cereals are excellent sources of fiber. Bran is an alternative source. Some people find it helpful to sprinkle 2 or 3 teaspoons of unrefined miller's bran on high-fiber cereal or fruit 2 or 3 times a day. Miller's bran also mixes well with applesauce, which also contains fiber. To work well, fiber must be consumed with plenty of fluids. Increased physical activity is also helpful because it stimulates contractions in the intestine, which helps move stool along.

Treatment of an underlying disease that is causing constipation may relieve the problem. Likewise, when a drug contributes to or causes constipation, a doctor may lower the dose or substitute another drug.

Laxatives and stool softeners are sometimes needed if changes in diet, physical activity, and drugs are insufficient. Most laxatives are safe for long-term use, whereas others should be used only occasionally. Some are better for preventing constipation, whereas others can be used for treating it. All laxatives must be used with caution, however, because overzealous use can lead to diarrhea, dehydration, or abdominal cramps.

Bulking agents, such as psyllium and methylcellulose, are laxatives that help hold water in the stool and add bulk to it. The increased bulk stimulates the natural contractions of the large intestine. Bulkier stools are softer and easier to pass. Bulking agents act slowly and gently. These agents generally are taken in small amounts at first. The dose is increased gradually until regularity is achieved. People who use bulking agents should always drink plenty of fluids.

Osmotic agents are laxatives that pull large amounts of water into the large intestine, making the stool soft and loose. The excess fluid also stimulates contractions. These laxatives consist of salts or sugars that are poorly absorbed. They may cause fluid retention in people with kidney disease or heart failure, especially if used frequently or in larger-than-recommended doses. Some contain magnesium and phosphate, which can be partially absorbed into the bloodstream, resulting in harm to people with kidney failure.

Stimulant laxatives contain substances that directly stimulate the walls of the large intestine (such as senna, cascara, and bisacodyl), causing them to contract. Taken by mouth, stimulant laxatives generally cause a semisolid bowel movement in 6 to 8 hours. However, stimulant laxatives may cause cramping. Some are available as suppositories. When taken as suppositories, these laxatives often work in 15 to 60 minutes. The body can become dependent on stimulant laxatives if they are not used correctly. For these reasons, stimulant laxatives are best used only for brief periods. If longer use is needed, they should be used no more often than every third day and under a doctor's supervision. They can help prevent constipation in people who are taking drugs that almost always cause constipation, such as opioids.

Stool softeners, such as docusate, help water to penetrate the stool more easily and soften the stool. Some people find the softened nature of the stool unpleasant. Used alone, stool softeners are unlikely to be helpful. Softeners are most helpful when taken together with laxatives for people who must avoid straining because they have hemorrhoids or have recently undergone surgery.

Prevention

A combination of an adequate intake of fluids, adequate exercise, and a high-fiber diet best prevents constipation. Laxatives are sometimes a helpful addition to these measures. For example, when a person needs to take a potentially constipating drug, a stimulant laxative along with increased intake of dietary fiber and fluids helps prevent constipation.

See the sidebar The Laxative Habit.

See the table Drugs and Agents Used to Prevent or Treat Constipation.