17 Causes Of Constipation - A Dietitian Explains

Constipation can be classified as primary or secondary causes:

With that said, let’s break down the primary and secondary CC causes that may be associated with causing bowel movement dysfunction...

Primary causes

1. Normal transit or functional constipation (most common)

• Characterized by muscles in the colon functioning properly (not too fast or too slow) and bowel movements are at the right speed but still, caused by your stool being too hard or too difficult to pass.

2. Slow transit

• Characterized by reduced motility, delayed movement, of the stool through the large intestines caused by an underlying dysfunction and abnormality of the colonic smooth muscle or neuropathy.

3. Evacuation disorder

• Characterized by the inability to correctly relax and coordinate the abdominal and anorectal muscles (pelvic floor muscles) to have a bowel movement from the rectum.

4. Mixed type

(combination of the above, eg slow transit and pelvic floor disorder)

•  Combination of the above symptoms

Secondary Causes

5. Medications

• Analgesics (NSAIDs, opioids)
• Antihypertensive agents (diuretics, calcium channel blockers)
• Antidepressants
• Antihistamines
• Antiparkinson agents
• Metallic ions

6. Neuropathy

• Autonomic neuropathy
• Hirschsprung disease
• Amyloidosis
• Central nervous system (CNS) lesion
• Parkinson disease

7. Metabolic disorders

• Diabetes
• Hypothyroidism
• Hyperparathyroidism
• Metabolic and electrolyte imbalance (hypocalcaemia, hypokalaemia, hypomagnesaemia)

8. Idiopathic and other associated conditions

• Paraneoplastic syndromes
• Eating disorders
• Diet: low fiber, low intake, high protein
• Colonic obstructions
• Mass lesions
• Pseudo-obstruction
• Cancer
• Stricture

Primary Constipation

Primary CC is a symptom-based disorder (1). This happens due to dysfunction of the colon muscles contracting and stimulating together to move the stool towards the rectum in a coordinated and predictable fashion. In other words, arise from intrinsic defects in colonic function or malfunction of the defecation process (1). These causes are often considered after secondary causes of constipation are ruled out (3). In this case, with no obvious alarm causes identified for secondary chronic diseases in medical history, empiric treatment often starts with fiber and/or laxative treatment (3).

With primary CC, there are several subtypes, of which can overlap and are rare, but occasionally must be taken into consideration when CC remains unresponsive to treatment (1):

• Normal transit / IBS-C
• Slow Transit Consti
• Pelvic Floor / evacuation disorders
• Mixed type

Which we broke down and went into detail in our first article on ‘What is Constipation and its Symptoms’.

Diagnostic criteria for constipation

Chronic constipation is characterized by symptoms of unsatisfactory defecation with infrequent stools, difficult stool passage or both (2). These symptoms must be present for at least 3 of the previous 12 months (2). To break the symptoms down even further, difficult stool passage includes:

• Straining
• A sense of difficulty passing stool
• Incomplete evacuation of bowel movements
• Hard/lumpy stools
• Prolonged time to stool
• or need for manual manoeuvres to pass stool

Slow transit and pelvic floor disorders are two different subtypes of constipation. Slow transit is caused when a bowel movement has longer transit time through the colon.

Whereas with pelvic floor / evacuation disorders is caused by the inability to have the final ‘push’ of the stool out of the rectum.

Potential Causes of Primary Constipation 

9. Lifestyle Factors

• Lack of movement
• Question to ask: Do you have low levels of physical activity, less than 30 minutes of movement each day?
• This causes decreased stimulation of gut muscles
• Changes in routine

• Our bowel movements work in a routine rhythm, changing eating, sleep, and toilet habits times confuses our bodies natural patterns, similar to when sleep is affected when we travel to different time zones and we’re out of our normal schedule.
• Ignoring the urge to go

• When we stop the natural urge to have a bowel movement, this allows more time for our body to absorb water from our stool, making our stool more compact and dry, thus harder for our gut to pass.
• Childhood toileting

• Yes, these types of bodily functions, being pressured or interrupted during defecation, may be a root cause adapted all the way back to childhood toileting! Individual’s bodies may have developed poor bowel habits and never corrected themselves.

10. Dietary Factors

• Not eating enough fiber
• Question to ask: are you meeting your 30g fiber goal per day, with a focus on whole grain fiber?
• Whole grain and plant fibers help to add bulk to our stool which provides our gut more to work making it easier to push out.
• Also, not eating enough overall, such as eating disorders, will cause the same effect on our stool load.
• Lack of hydration

• Question to ask: Are you drinking at least 50 ounces of water (1.5L) of fluid per day?
• Fluids help to keep our stool at a healthy consistency, smooth and snake-like in shape, so that it's painless and easy for our gut to pass.

11. Psychological

• Stress, anxiety or depression
• This disrupts our gut-brain connection. This causes altered communication from our brain to our gut musicals, aka the natural gut-brain axis, to have normal, consistent bowel movements.
• History of physical or psychological abuse

• Trauma can also have a similar effect on our bowel habits. This too can cause disconnecting between our gut-brain axis impacting the muscles guts properly functioning in defecation. 

Secondary Constipation

Secondary constipation happens as a result of many different factors, as seen in the table above. Secondary causes are related to organic disease, systemic disease or medication, such as anorectal and colonic diseases, diet, drugs, metabolic disorders (diabetes or hypothyroidism), and neurological problems such as parkinsons (1)(3).

Many diseases involving the nervous system may cause chronic constipation such as -- neuropathy, diabetes, and other endocrine disease as well as uncommon causes like Chagas disease and Hirschsprung’s disease. (3)

Less common but complex and serious secondary causes of constipation can be more mechanical in nature such as causing inflammation (diverticulitis or Crohn’s) which can cause our intestines to scar and narrow. Other causes are tumors or growths in the colon that physically block bowel movements.

Secondary CC can be an acute or chronic problem. These causes are often considered and ruled out first and often identified in an individual's detailed past medical history (3). This might require stool disimpaction, withdrawal of medications or correcting the colonic issue (1).

Therefore, secondary causes will only be relieved after the underlying health issue(s) are resolved (1).

Medication and Constipation 

Drugs causing constipation are very common side effects (3). A detailed medical history should be done to pinpoint potential root cause of medication induced constipation. Antihypertensive medications reduce smooth muscle contractility, thus impairing bowel function (3). Patients that have constipation should swap their antihypertensive medications (clonidine, calcium antagonists, and ganglionic blockers) to be on beta-blockers, angiotensin-converting enzyme inhibitors or angiotensin II receptor antagonists (3).

Antidepressants also commonly cause constipation symptoms and side effects, specifically tricyclic antidepressants (3). Alternatively, what might be more preferred in constipation patients are 5HT reuptake inhibitors and 5HT norepinephrine reuptake inhibitors as they are less likely to cause constipation (3).

Another medication that frequently causes constipation are oral iron supplements (3). When iron supplementation is deemed necessary in these patients, intravenous iron supplement is best (3).

Other drugs that fall under the category of increasing constipation are aluminum-containing drugs, sucralfate and antacids, and can be swapped out for proton pump inhibitors (3). Analgesics, opiates and cannabinoids, can be switched to a different class of opiates or in combination with a peripherally active opiate receptor antagonist (3).

Anti-parkinson, antiepileptic, and antipsychotic drugs should be replaced due to their blocking of neurotransmitters and parasympathetic nerve system function for bowel movements should be avoided when possible or combined with consistent use of laxatives (3).

Lastly, antihistamines, antispasmodics and vinca alkaloids should also be swapped, see suggested drug replacement table below as a simple reference guide when medically apperirate in constipated patients (3).

Medications that commonly cause constipation:	In constipated patients, alternative options to discuss with your healthcare practitioner:
Analgesics (NSAIDs, opioids, cannabinoids)	Switch to another class of analgesics or opiate in combination with peripherally active opiate receptor antagonist (naloxone or methylnaltrexone)
Antihypertensive agents (diuretics, calcium channel blockers)	Beta-blockers, angiotensin-converting enzyme inhibitors or angiotensin II receptor antagonists
Antidepressants	5HT reuptake inhibitors and 5HT norepinephrine reuptake inhibitors
Antihistamines, antispasmodics and vinca alkaloids	Unclear
Antiparkinson agents, antiepileptic and antipsychotic drugs	Avoided if possible or combined with regular use of laxatives
oral iron supplements	Intravenous iron or oral iron supplement in combination with laxatives
Aluminum-containing drugs	Proton pump inhibitors

Neurogenic bowel dysfunction and Constipation

Conditions such as spinal cord injuries, multiple sclerosis, and Parkinson's disease commonly cause constipation (3). These types of neurogenic diseases cause imparied colonic motility and pelvic nerve dysfunction, which can lead to the origin of constipation (3). There are also systemic factors that make the cause of constipation in these individuals very complex.

Constipation could also be associated with altered textured diets, liquid diets, impaired mobility, and/or psychological disturbances (3). In addition, medication used in treatment for these conditions may cause constipation (3). Because of this, it is advised in these patients to have regular use of laxatives for regularity in bowel movements (3).

Thus, so often medical conditions are listed out as a cause of constipation. However, there is very little discussion regarding what predominates in these cases, is it the condition or the type of constipation?

For example, is constipation related to Parkinson’s disease secondary to nerve dysfunction in the bowels, thus creating more of a slow transit subtype of constipation? ... Or is it related to medications used to manage the condition? Or maybe perhaps it is both?

Diabetes and Constipation

For instance uncontrolled blood sugars, leading to neuropathy that causes intestinal enteropathy may be the principle underlying mechanism for diabetic patients, but the exact cause of diabetes related secondary CC is poorly defined in the literature (3).

For both patients with type 1 and type 2 diabetes, no single risk factor for the development of GI issues has been identified (3). 

Both hyperglycemia and hypoglycemia were shown in acute and chronic patients to impair their enteric neuron regulation and cause constipation (3). Constipation for these individuals may improve or resolve with better controlled blood sugars, and thus optimizing glycemic control should be the first priority (3).

Iodine and Thyroid mediated Constipation

Likewise, general strategies, such as ensuring iodine sufficiency in hypothyroidism and making sure to avoid impacting medication efficacy with meal timing, might be especially helpful for preventing the cause of thyroid mediated constipation.

I could go on, but what I’m getting at is that there may be some lifestyle factors which can help with managing aspects of disease states which stimulate secondary causes of constipation, and this appears to not be part of the current discussion surrounding constipation in the literature.

Further, some people with slow transit constipation have no nerve cell deficiencies, but simply have inadequate calorie intakes, which may be the root cause of slowing their GI motility.

The root cause approach:

The root cause could add more to the constipation discussion beyond simply telling people to employ the same simple strategies they’ve been trailing out for years -- fiber and fluids.

And thus, better lifestyle related management of certain disease states, such as the above, may be helpful in improving the cause of secondary constipation. Unfortunately, there aren’t many studies that dive into the efficacy of constipation treatment with OTC medications or lifestyle changes for these types of secondary conditions.

With so many underlying causes and different types of chronic constipation, getting specialized medical advice is critical. Even still, figuring out the root cause and best treatment can take time to sort out, especially without good record keeping of symptoms, diet, stool consistency, etc.

Our Summary

• The purpose of defecation is an essential bodily function to evacuate the body's toxins and metabolic wastes and on a consistent basis. 
• Constipation should be taken seriously, as the extra time the stool has in the colon allows for toxins to potentially leak back into your system, causing and manifesting more serious health problems.
• Primary causes of constipation happens due to dysfunction of the colon muscles contracting and stimulating together to move the stool towards the rectum in a coordinated and predictable fashion.
• There are 4 subtypes of primary CC: 
• Normal transit or functional constipation (most common)
• Slow transit
• Evacuation disorders
• Mixed Type
• Secondary causes of constipation are related to organic disease, systemic disease or medication, such as:
• Anorectal and colonic diseases
• Poly-pharmacy and medications
• Metabolic disorders (diabetes or hypothyroidism)
• Neurological problems
• Idiopathic and other associated condition such as obstructions, diet, eating disorders, etc
• With so many potential underlying causes and different types of chronic constipation, primary or secondary, understanding the root cause of an individual's constipation and getting specialized medical advice is critical for long-term solutions to resolve CC.