Constipation: Overview and Risk Factors

The term "constipation" refers generally to the difficult or infrequent passage of stool. A common definition of constipation is fewer than 3 spontaneous, complete, bowel movements per week. It is the most common gastrointestinal complaint in the United States, with an adult prevalence of about 15% to 20%.

Constipation is also a common pediatric condition. Many cases are related to behavioral issues. However, the condition in children can result from dietary causes, which include fiber deficiencies, dehydration, and dairy intolerance.¹ Constipation also occurs in cystic fibrosis and lead poisoning.

Primary Causes

The most common primary cause of constipation is slow transit of stool through the colon, which accounts for 95% of cases. Less common primary causes include pelvic-floor dysfunction, anismus, and an irritable colon.

Secondary Causes in Adults

Common identifiable secondary causes in adults include:

• Medications. Constipation is a common side effect of antihistamines, narcotics, antacids, calcium channel blockers, tricyclic antidepressants, and many other drugs. Drugs are a particularly common contributor in older adults.
• Smoking cessation. Constipation is a temporary result of nicotine withdrawal.²
• Parkinson's disease.
• Anatomical obstruction (eg, tumor, stricture, or third-trimester pregnancy).
• Hemorrhoids, abscesses, fistulae, and fissures can decrease the desire to defecate due to pain and induce constipation.
• Diet (see Nutritional Considerations).
• Hormonal factors (eg, hypothyroidism).

Symptoms and Signs

• Hard, dry stool, which is difficult to pass or leaves the sensation of incomplete evacuation.
• Infrequent bowel movement.
• Bloating and abdominal discomfort. These symptoms are more common in irritable bowel syndrome (IBS) than in simple constipation. IBS can be differentiated from simple constipation by the presence of other digestive symptoms (see Irritable Bowel Syndrome chapter).
• Lower back pain. However, pain is uncommon in idiopathic chronic constipation.
• Rectal bleeding (eg, stercoral ulcerations/erosions).
• Hemorrhoids or, uncommonly, headaches due to straining in adults.

Risk Factors

The highest reported prevalence of constipation occurs in persons over 60 years of age, followed by children under age 10. The association with age is largely attributable to other factors, such as medication and diet. For unclear reasons, whites report constipation less frequently than other racial groups, and women are affected approximately twice as often as men. The condition is more common in individuals with relatively low incomes and less education.

Additional possible risk factors include:

• Family history.
• Pelvic floor dysfunction.
• Pelvic and abdominal surgery.
• Childbirth.
• Anorectal problems.^3,4