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Risk Factors For Constipation

Stool is formed in the colon, which is at the lower end of the gastrointestinal tract. By the time digested food reaches the colon, most of the nutrients have been absorbed. The colon’s primary job is to remove excess liquid from intestinal contents. A large number of beneficial bacteria colonize the colon and help with digestion of any remaining nutrients. Muscular peristaltic waves propel the stool (while it is in the process of being formed) toward the rectum. The stool is aided in its passage through the colon by mucus, which provides lubrication.

Bulk-forming fiber and water are essential to the healthy formation of stool. Insoluble fiber provides bulk to the stool and retains enough water to keep the stool pliable (Hsieh 2005). Likewise, adequate moisture is needed to keep the stool soft and prepare it for evacuation. There is, however, some disagreement among physicians about the role of fluid intake in constipation. Some studies have reported that liquid intake is not associated with constipation (Whitehead 1989).

For the most part, doctors usually consider the following to be the causes of constipation:

  • Lack of exercise. Constipation has been shown to be related to inactivity (Simren 2002). Abdominal and intestinal muscles work together to move the bowels. Weak abdominal muscles can contribute to weak bowel movements.
  • Some medications. Some pain medications, especially narcotics, can cause constipation, as can some antidepressants, iron supplements, and calcium supplements (Muller-Lissner 2002). Other medications that can cause constipation include calcium channel blockers, psychotropic drugs, and anticholinergics. Inadequate thyroid hormone supplementation is also thought to cause constipation.
  • Certain diseases. Tumors and some diseases may produce a rapid change in bowel movements, or even the cessation of all bowel movements.

During the diagnostic evaluation of constipation, physicians will attempt to determine if the condition is caused by an underlying disease, medication, or dietary cause. Constipation can be defined as the presence of two or more of the following symptoms, occurring for at least 12 weeks in the preceding 12 months (symptoms 1 through 5 must occur at least 25 percent of the time when defecating) (Corazziari 2004; Voskuijl 2004; Whitehead 2003):

  1. Straining
  2. Lumpy or hard stools
  3. Sensation of incomplete evacuation 
  4. Sensation of anal-rectal obstruction or blockage
  5. Manual maneuvers to facilitate defecation
  6. Infrequent (fewer than three) bowel movements per week

Measurement of colonic transit time (how long it takes stool to move through the colon) is sometimes used to evaluate patients with chronic constipation (Corazziari 2004; Sakakibara 2004).

Complications of constipation include hemorrhoids (which are caused by straining to have a bowel movement) and anal fissures (which are tears in the skin around the anus). As a result, rectal bleeding (appearing as bright red streaks on the surface of the stool) may occur (Chiarelli 2000; Pfenninger 2001; Wald 2003).

Sometimes straining causes a small amount of intestinal lining to push out from the anal opening. This condition is known as rectal prolapse. Treatment requires pushing the prolapsed portion of the bowel back into the body, which can be done manually in a doctor’s office. In some cases, incarcerated rectal prolapse (i.e., the prolapsed portion of the bowel becomes trapped) may occur. This is an emergency that requires surgery (Sarpel 2005).

Constipation can contribute to a loss of bladder control by weakening the pelvic floor muscles as a result of straining. A full bowel pressing on the bladder, causing it to empty prematurely or block the outflow of urine, is not uncommon. People who have bladder control problems often do not drink enough fluids for fear of incontinence, which can also worsen constipation (Chen 2003).

Among middle-aged or elderly people, severe constipation or an abrupt change in bowel habits should prompt a thorough medical evaluation. Patients should be screened for thyroid hormone levels as well as electrolyte levels (such as potassium, calcium, glucose, and creatinine). Other measures should include evaluation of fecal occult blood and a white blood cell count. Colorectal screening is mandatory in patients older than 50 years who experience a change in bowel habits. Screening tests include sigmoidoscopy or colonoscopy (flexible tube or virtual) and barium enema. These tests are used to detect colorectal cancer. Of all the diagnostic tests available, flexible-tube colonoscopy is superior at detecting polyps (defined as precancerous lesions). Polyps can be removed during flexible-tube colonoscopies.

Constipation is also a relatively common complaint among children, affecting up to an estimated 10 percent at some point. Although constipation in children is usually caused by diet, it may be an indication of a significant organic disorder that can be determined by a thorough medical history and physical examination. Constipation that is present from birth or that begins in the neonatal period is most likely congenital in origin.