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Constipation Myths and Facts

When it comes to health issues, bowels are big business. Bowel movements are part of everyday life, and we notice immediately when our routine changes. Constipation, from the Latin word constipare (“to crowd together”) is something almost everyone has some experience with. In most cases, it’s an occasional annoyance that resolves quickly. For others, particularly the elderly, constipation can be a chronic condition, significantly affecting quality of life.  Depending on the question and the sample surveyed, prevalence seems to vary widely.  It’s estimate that there are 2.5 million physician visits per year in the USA, and the costs of management are estimated at about $7.5 billion annually. It’s not a trivial issue.

One of the biggest challenges in interpreting both individual patient situations, as well as the literature overall, is understanding what’s defined as “constipation”. One person’s regular routine may be another person’s constipation. From my dialogue with patients, personal definitions seem to vary. Some panic after a single missed bowel movement, while others may be unconcerned with daily (or even less frequent) movements. What’s the optimal frequency? It depends. Infants may be 3x/day. Older children may be once daily. Adults may be daily or less frequently.  The literature generally, though not consistently, defines constipation as a delay or difficulty in bowel movements ( usually less than 3 per week) lasting two weeks. Symptoms can include infrequent, painful bowel movements, straining, and lumpy or hard stools.  When these problems last for more than three months, it’s termed chronic constipation. When constipation is accompanied by other symptoms like bloating, diarrhea, and abdominal pain, it may be termed  irritable bowel syndrome (IBS).

There are multiple causes of constipation. It may be a consequence of other illnesses (e.g., high/low thyroid, diabetes, cancer, and neurological diseases like multiple sclerosis). Drugs, both prescription and over-they-counter, can also cause constipation.  Primary or idiopathic constipation is a diagnosis of exclusion, after other causes have been ruled out.  If there are no signs of a more serious underlying condition, treatments can be considered.

Many have firmly-held opinions about their colon and their bowel movements: what’s normal, and what’s not. And there are equally strong opinions about the causes of, and solutions to, constipation. But despite the ubiquity of constipation and the firmly-held opinions on treatments, there’s a sizable chasm between practice and evidence.  This is an area with crappy (sorry) data, and it’s hard to sort out what are true treatment effects. But an absence of evidence isn’t evidence of absence, so we’re challenged to make the best decisions possible, despite a disappointing evidence base. Here are some common statements I’ve encountered, and an evidence check on their veracity.

The colon is the root of all illness

Colonic dysfunction as constipation has been described as a cause of disease since at least the 16th Century BC. It’s been a recurring medical motif as long as medicine has existed, starting with ideas of internal putrefaction, and later, once germ theory arrived, became a worry about autointoxication. This theory proposed that unnamed “toxins” were being absorbed from the bowel and causing systemic disease.  Now discredited in science-based medicine, these ideas continue to manifest today, largely in the realm of CAM with its warnings to “detox”, irrigate our colon, and indulge in other ritualistic “cleansing” practices. So today the colon continues to be blamed for all manners of illness, including eczema, cancer, high blood pressure, allergies, and more. There’s no evidence  to substantiate these claims.

I need to have a bowel movement at least every “X” to avoid toxins/allergies/chronic disease/certain death

This argument is an extension of beliefs about the necessity of bowel movements to avoid systemic disease. Interestingly, over hundreds of years, there’s always been the idea that constipation is a modern disease, one of urbanization and civilization: dietary changes, the busy pace of life and a lack of exercise.  So if you don’t feel constipated, you aren’t. Bowel habits can be evaluated on their own merits. As long as they’re not painful or hard, there is no ideal frequency. In the absence of constipation, the flushing of the colon, or the use of laxatives or other purgatives is at best unnecessary, and at worst, potentially harmful.

A lack of fibre can cause constipation, and fibre supplements are effective constipation treatments

The granddaddy of fibre cereals, All Bran, appeared on the market in the 1900s as a treatment for the diagnosis of the day,  autointoxication of the colon. Since then, fibre has held a special place in the armamentarium of health professionals and CAM advocates alike: It’s not only natural, but nature’s little broom, right?

Fibre, from cereal or other foods, serves multiple purposes in the bowel. It adds bulk to the stool and can increase the frequency of bowel movements. But there is a lack of correlation between dietary fibre intake, and the risk of constipation. And in patients given fibre supplements, the response in patients with chronic constipation is erratic. Fibre, particularly bran and other insoluble fibres causes gas formation, which can limit acceptance. Soluble fibres, like psyllium (Metamucil) are better tolerated.

Studies suggest that that low fibre diets may be a a contributing factor to constipation in a subset of patients, who may  respond to higher fibre diets. Consequently, Fibre supplements may be useful in some patients with mild or occasional constipation. But in more severe cases of chronic constipation, fibre can actually aggravate symptoms,and does not appear to be an effective therapy.

Drinking more fluids can help reduce the risk of constipation

The idea that consuming more water will result in softer, easier to pass stools hasn’t been substantiated when studied in patients with chronic constipation. Studies in the elderly have also failed to reveal an association between increased fluid intake and constipation. Constipated children, randomized to consume different amounts of fluid, didn’t experience any changes in stool frequency, consistency, or ease of defecation. Unless there’s evidence of dehydration, consuming extra fluid on its own is unlikely to make any difference in cases of constipation.

Exercise can help constipation

In most patients with constipation, this statement is true. There’s an established relationship between our activity level and our bowel habits, giving us the luxury of sleeping several hours without interruption. There seems to be a relationship between exercise levels and incidence of constipation, though across several studies, it’s not clearly a causal relationship. And in cases of vigorous exercise (e.g., running) there is clearly evidence of a significant increase in activity. While it’s not possible to do a truly randomized, double-blind trial, the evidence available supports the use of  physical exercise can be helpful for modest constipation, but it does not seem to be effective for severe cases.

Stool softeners are effective
Stool softeners (e.g., docusate sodium (Colace)) are among the most popular products prescribed for the prevention or treatment of constipation. They’re often a reflex prescription that accompanies narcotic prescriptions, because constipation is a frequent side effect of narcotic drug use, mainly due to effects on transit time through the colon. Stool softeners are essentially soap, and the theory is that they make the stool easier to pass. Despite their widespread use, there’s no good evidence that docusate sodium or docusate calcium are effective for the treatment of constipation. I find it quite fascinating that docusate sodium is one of the active ingredients in Corexit, last seen being dumped in large quantities into the Gulf of Mexico to disperse the Deepwater Horizon oil spill. Presumably the evidence is better for that indication.

Natural or synthetic, the drugs don’t work

Before treating constipation, getting an understanding of symptoms, other medications, and other illnesses is important. In cases where reversible factors  have been ruled out, drug therapy may be warranted. Despite the lack of good evidence, dietary and lifestyle changes usually precede drug therapy. In cases that don’t respond or resolve on their own, medications are next. Broadly, categories of treatments include bulk-forming products, stool softeners, osmotic agents, and stimulant laxatives.  Products available are a mix of naturally-derived and synthetic products. Some of the most popular laxatives are naturally-derived. The strange smell of Senokot tablets gives a clue to its origin: They’re senna glycosides, a product of the senna plant. The naturally occuring glucosides it contains are colonic irritants, stimulating colon contraction. Metamucil is psyllium seed husks, which swell into a gelatinous mass in the stomach, carrying water and bulk to the colon. Most of the other fibre supplements are naturally-derived as well.

The other commonly used products are synthetically derived. Milk of magnesia, despite its natural sounding name, is a suspension of magnesium hydroxide.When consumed, most of the magnesium isn’t absorbed, and it pulls fluid with it (via osmotic pressure) when it’s shunted to the colon. Polyethylene glycol (PEG) works this way, as does lactulose, a non-digestible sugar. The cathartics taken before endoscopy are all osmotic agents, too.

Bisacodyl (Dulcolax) is another popular over-the-counter product. A stimulant laxative like senna, bisacodyl stimulates colon contraction.

Despite the number of products, and prevalence of constipation, the evidence base for drug treatments is weak. There’s little head-to-head evidence that has pitted on treatment against another. So we’re largely left to make inferences from poor studies on different populations. The best evidence (which is still pretty weak) exists for the osmotic agents like PEG. Some evidence exists for psyllium, but it’s underwhelming. There’s evidence for lactulose as a treatment, as well. An excellent systematic review from the Oregon Evidence-Based Practice Center summarizes the evidence base in greater detail.

Probiotics can be effective for constipation

Probiotics, covered in depth by Mark Crislip already, are live microorganisms administered with intent of a therapeutic effect. If you like yogurt that does double duty, you’ll probably see brands that include Bifidobacterium and Lactobacillus, and, depending on your national regulator, there may be vague health claims about intestinal “wellness” on the label. The idea of probiotics for constipation is at least plausible, as probiotics have the potential to disrupt the colon’s bacteria ecosystem – if only to a very limited extent, as Mark noted in his post.  For constipation, their effectiveness hasn’t been demonstrated though. A systematic review published in 2010 examined the data supporting their use in adults and children.  Five high quality trials were identified and the results were unimpressive:

Data published to date suggest that adults with constipation might benefit from ingestion of B. lactis DN-173 010, L. casei Shirota, and E. coli Nissle 1917, which were shown to increase defecation frequency and improve stool consistency. However, in some cases, even if there was a significant difference in results, their clinical relevance is unclear.

Their conclusion:

Until more data are available, we believe the use of probiotics for the treatment of constipation condition should be considered investigational.

Overall, not encouraging. And little reason to recommend their use. That’s the opinion of some regulators, too. The European Food Safety Authority has largely rejected general health claims for probiotics.

Taking laxatives continuously is dangerous and leads to tolerance and then dependence

This is a common myth, but not substantiated by fact. [PDF] As a pharmacist I see a lot of chronic laxative use – some appropriate, and some clearly inappropriate. Something that was planted in my head in pharmacy school was the warning that chronic use would lead to dependence, and a near-certain risk of constipation if their use was suddenly stopped.  The warning is primarily with the stimulant laxatives, which have been believed to affect nerve conduction and muscle damage, largely based on anecdotal evidence. Microsope examination of colon tissue in chronic laxative users reveal some differences from normal subjects. But whether these changes are caused by stimulant laxatives, or are a product of an underlying disorder, is unclear. The best evidence we have suggests that risks of of most  laxatives, when used to treat constipation, at recommended doses, is probably small.  Risks seem restricted to patients with severe symptoms on high doses of stimulant laxatives.  Notably, because laxatives are generally not even absorbed, there is no risk of them directly causing nervous system effects. Consequently, there’s no risk of a actual addiction, through there’s no question that they can be misused. Misuse beyond the treatment of constipation can be problematic, potentially leading to electrolyte disturbances.

Children are little adults

False. Constipation is children is common, and it causes distress to parents, too. I’ve spoken with parents of infants only weeks old, already set on giving their child a suppository because the “regular” bowel movement is hours late. In infants, parents often ask me about iron-free formulas, thinking the iron may be causing constipation. However iron-fortified formulas haven’t been shown to be more constipating that iron-containing formulas. So switching to an iron-free formula may have no effect, and introduce the challenge of ensuring adequate iron intake.

The most common cause of constipation in children is functional constipation – constipation without an intrinsic cause, usually caused by children deliberately delaying or avoiding bowel movements, usually due to a painful past movement. Delaying causes further constipation, and further pain with bowel movements. Functional constipation is the cause of almost all constipation in children. Constipation that’s accompanied by abdominal pain, nausea, anorexia, or vomiting needs a physician examination to rule out other causes.

Despite its frequency, constipation in children rarely lasts and generally doesn’t require medication. Which is good, because there’s little evidence to demonstrate that laxatives are effective in children. A systematic review published earlier this year summarized the evidence base. Like treatment for adults, the data are limited. Because of the lack of evidence, dietary changes, while also not well supported by evidence, should precede any drug therapy. Acute treatments should be followed with longer term strategies to prevent further episodes. While the effectiveness of fibre for the treatment of constipation in children hasn’t been demonstrated, encouraging fibre-rich fruits or vegetables as a first step may plausibly help, and have numerous other health benefits as well.

Conclusion

Constipation is is common condition, yet there’s little high quality evidence to guide our actions. Myths about constipation further complicate treatment strategies. In the absence of high quality evidence, it would seem most conservative to carefully evaluate each situation for potentially causal factors, and introduce the treatments backed by the best evidence only after core dietary and lifestyle factors have been implemented.

Posted in: Science and Medicine

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