Chronic diarrhea is defined as the passage of loose or watery stools lasting four weeks or longer. This persistent condition should never be accepted as a normal consequence of aging, as it carries a high risk of dehydration, malnutrition, and electrolyte imbalance. Older adults are uniquely susceptible due to the combined effects of multiple health conditions, the use of numerous medications, and age-related changes in gastrointestinal function. A thorough medical investigation is always necessary to identify the underlying cause.
Medications and Polypharmacy
The complexity of chronic diarrhea in older adults often begins with polypharmacy, the concurrent use of multiple medications. Many commonly prescribed drugs have a direct or indirect effect on bowel function, making medication side effects a frequent cause of chronic diarrhea. A systematic review of all current prescriptions is a primary step in diagnosis.
Common culprits include nonsteroidal anti-inflammatory drugs (NSAIDs) and proton pump inhibitors (PPIs), which can directly irritate the gut lining or alter the gut microbiome. Metformin, used for type 2 diabetes, often causes diarrhea by increasing unabsorbed bile acids and altering gut motility. Other cardiovascular medications, such as ACE inhibitors and the heart drug digoxin, can also trigger chronic loose stools.
The overuse or misuse of laxatives is a common cause of chronic watery stool. While intended to treat constipation, chronic reliance on osmotic or herbal laxatives can lead to dependence and persistent diarrhea. This pattern creates an osmotic imbalance, drawing excessive water into the bowel. Recognizing drug-induced diarrhea is challenging because symptoms may not appear until weeks or months after a medication is started.
Infectious Agents and Immune-Mediated Colitis
Infectious causes of chronic diarrhea are severe due to the compromised immune status often seen in older adults. The bacterium Clostridioides difficile (C. diff) is the most prevalent infectious agent, primarily affecting individuals over age 65. This organism proliferates when the intestinal flora is disrupted, most often following antibiotic use.
C. diff infection manifests with severe, watery diarrhea, abdominal cramping, and fever, sometimes progressing to life-threatening conditions like toxic megacolon. The risk is higher for those who have been hospitalized or residing in long-term care facilities due to environmental exposure and frequent antibiotic use. The use of acid-suppressing medications, such as PPIs, has also been linked to an increased risk of acquiring C. diff infection.
Beyond acute infections, microscopic colitis is an immune-mediated condition causing chronic watery diarrhea in older adults. It includes two subtypes, lymphocytic colitis and collagenous colitis, diagnosed by microscopic examination of colon tissue. The colon appears normal upon standard endoscopy, necessitating biopsies for diagnosis. Microscopic colitis is associated with older age, particularly in women, and its onset is frequently linked to the use of NSAIDs, SSRIs, and PPIs.
Structural and Motility Changes
Physical and functional alterations within the digestive tract structure and its neural control contribute to chronic diarrhea in the elderly. One cause is fecal impaction, where a mass of hardened stool becomes lodged in the rectum or colon. This severe constipation leads to what is known as overflow diarrhea.
In overflow diarrhea, liquid stool produced higher up cannot pass the solid obstruction, leaking around the hardened mass as chronic, watery seepage. This condition is common in individuals with reduced mobility, neurological disorders, or those taking constipating medications like opioids. Diagnosis requires a physical examination to detect the impacted stool, as misinterpreting the leakage leads to inappropriate treatment.
Age-related changes can also affect the nerve and muscle coordination responsible for normal bowel movements. Conditions like Irritable Bowel Syndrome (IBS) may present or worsen later in life, characterized by chronic abdominal pain associated with changes in stool frequency and form. Investigation must also rule out colorectal cancer, a structural cause that can obstruct the bowel or cause chronic irritation and bleeding, necessitating a colonoscopy.
Dietary Factors and Malabsorption
The ability to process and absorb nutrients can decline with age, making dietary factors and malabsorption important considerations for chronic diarrhea. A common issue is lactose intolerance, where the production of the enzyme lactase decreases, making it difficult to digest the sugar in milk products. The unabsorbed lactose then draws water into the colon, causing osmotic diarrhea.
Certain food additives and artificial sweeteners, such as sorbitol and mannitol, are poorly absorbed by the small intestine and function as osmotic agents. These sugar alcohols are often found in “sugar-free” products and medications, and their consumption can lead to chronic watery stools. A careful dietary history can reveal these ingredients as the source of the problem.
Malabsorption syndromes involve the inability to absorb fats, proteins, or carbohydrates, often resulting in bulky, greasy, and foul-smelling diarrhea called steatorrhea. Conditions such as celiac disease (an intolerance to gluten) or chronic pancreatic insufficiency must be considered. Pancreatic insufficiency occurs when the pancreas does not produce enough digestive enzymes and may cause symptoms like micronutrient deficiency or unexplained weight loss.