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Underactive Thyroid and Constipation

By 1st March 2023May 24th, 2023Health Conditions

What is constipation?

Constipation is a common and often chronic digestive symptom that impacts patients throughout the world. It is estimated that 14% of the global population suffers from constipation with females experiencing this more frequently than males. [Source: Pubmed]

Constipation is where it’s hard to pass a stool. This can happen with or without the additional symptoms of IBS. These symptoms of IBS generally include:

  • Bloating
  • Pain
  • Abdominal discomfort

The diagnosis of constipation can be made using specific symptoms that are specified in the ROME diagnostic criteria for constipation. The ROME criteria for constipation term this gut issue, functional constipation.

For many with chronic constipation (with or without IBS) the term can mean that someone is experiencing a range of gut symptoms. These can include a reduced number of bowel movements per week, lots of straining, the sensation of incomplete bowel movements as well as the requirement of digital manoeuvres (the use of fingers to manually remove stool from the rectum). [Source: Pubmed]

Do I have constipation?

There are clear criteria that can be used to diagnose constipation. The diagnostic criteria for constipation state that 2 or more of the following need to be present for a diagnosis of functional constipation to be given.

  • Straining during more than ¼ (25%) of defecations
  • Lumpy or hard stools (Bristol Stool Form Scale 1-2) more than ¼ (25%) of defecations
  • Sensation of incomplete evacuation more than ¼ (25%) of defecations
  • Sensation of anorectal obstruction/blockage more than ¼ (25%) of defecations
  • Manual manoeuvres to facilitate more than ¼ (25%) of defecations (e.g., digital evacuation, support of the pelvic floor)
  • Fewer than three spontaneous bowel movements per week
  • Loose stools are rarely present without the use of laxatives
  • Insufficient criteria for irritable bowel syndrome (IBS)

The final point on this list (insufficient criteria for IBS) refers to the fact that for a diagnosis of IBS, recurrent abdominal pain also needs to be present. For many with constipation, pain may not be an issue.

This means that constipation can be an isolated symptom and not a type of IBS. [Source: ROME Foundation]

Is constipation the same as IBS?

While constipation can be a symptom of IBS, they are not the same thing.

This is due to the fact that the symptom of constipation can be present in isolation. Here, there can be slow bowel movements which involve straining and the sensation of incomplete evacuation. These symptoms are used to indicate constipation.

However, for a diagnosis of IBS recurrent abdominal pain is a symptom that is required. Therefore, if constipation is present with abdominal pain as well as symptoms such as bloating, then this will likely be diagnosed as IBS-C (irritable bowel syndrome with constipation). [Source: Pubmed]

Also Read: Where Is Constipation Pain Felt?

What causes constipation?

A range of factors may contribute to constipation. These causes of constipation can be divided into 2 categories.

  1. Primary constipation
  2. Secondary constipation

Causes of primary constipation include:

  • Irritable bowel syndrome (IBS)
  • Slow transit constipation (nerve or muscle related)
  • Dyssynergic defecation

Causes of secondary constipation include:

  • Metabolic (hypothyroidism)
  • Medications (opiates, calcium channel blockers, antipsychotics)
  • Neurologic disorders (parkinsons, spinal cord injury, diabetes mellitus)
  • Primary colonic disorders (stricture, cancer, anal fissure, proctitis)

This means constipation has many possible causes. It’s also possible for there to be an overlap with a number of these causes being present in each individual with gut issues such as constipation.

Each of these causes may then present further steps on how to address it. For example, if the constipation is caused by IBS, then working to identify and address the causes of the IBS would be the next step.

The same is also true for hypothyroidism and how this can impact gut health and constipation.  [Source: Pubmed]

How to treat constipation

Before considering in-depth testing or restrictive diets, there are foundational ways to support gut health and constipation. These ways to address constipation consist of dietary and lifestyle changes.

The first is fluid intake with poor hydration impacting the ability of stool to travel through the large intestine. Along with this, fibre intake can also work to support the bulk of the stool to support bowel movements.

Regular movement and exercise are also important to help with going to the toilet. This is due to the ability of movements to the contractions of the muscles required for bowel movements as well as the improved composition of the gut microbiome. [Source: Pubmed]

Is fibre helpful for constipation?

Fibre is described as a dietary substance that is resistant to the action of digestive enzymes. This can act to add bulk to the stool to support bowel movements. These bulk-forming fibres are referred to as insoluble fibres.

  • Sources of insoluble fibre include wheat bran, whole grains, corn, kale, kiwi, raisins, and lentils.
  • Sources of soluble fibre include: oats, peas, beans, apples, citrus fruits, carrots and barley.

Fibre can also be introduced into the gut by using psyllium husk (Plantago ovata) which contains a combination of soluble and insoluble. [Source: Pubmed].

Along with this, prunes, as well as flaxseeds, have also been found to help with constipation. [Source: Pubmed]. A 2020 study found flaxseeds to be more effective that the commonly prescribed laxative lactulose at improving functional constipation. [Source: Pubmed]

Fibre Foods

Fibre has been shown to:

  • Accelerate colonic transit time
  • Increase biomass (bulk)
  • Support the balance of the gut microbiome
  • Improve the pH of the colon. [Source: Pubmed]

However, in some individuals, particularly if there are symptoms of IBS (that include bloating and pain), the reduction in fibre may be a helpful way to improve symptoms. This may be in the form of a Low FODMAP diet.

This diet removes highly fermentable fibres and carbohydrates. However, this is described as a short-term diet to help reduce symptoms, rather than a treatment. [Source: Pubmed]

Why does an underactive thyroid lead to constipation?

Hypothyroidism is the term used to describe the underperformance of the thyroid gland. This leads to lower levels of thyroid hormones and can result in a range of issues such as:

  • Heart disease
  • Increased body weight
  • Dry skin
  • Constipation
  • Fatigue

In the majority of cases of an underactive thyroid, the issue is caused by the actual thyroid gland failing to produce adequate levels of hormones. This is referred to as primary thyroiditis. The remaining percentage is caused by other causes (referred to as secondary hypothyroidism) which can include issues with the pituitary gland. [Source: Pubmed]

In many developing parts of the world, the main cause of an underactive thyroid (hypothyroidism) that leads to constipation is low levels of dietary iodine. This is a key mineral that supports the production of thyroid hormones.

This has led many regions to support iodine intake by adding it to their salt to support thyroid health. Iodine can also be found in foods such as fish (such as cod and tuna), seaweed, shrimp, and other seafood. [Source: Pubmed]

In more developed regions of the globe, the cause of hypothyroidism is Hashimoto’s thyroiditis, an autoimmune disease. In this condition, the body’s own immune system attacks the thyroid gland leading to tissue destruction and suboptimal thyroid hormone production.

For Hashimoto’s thyroiditis, several approaches have been researched to support thyroid health.

These include:

Underactive thyroid and stomach problems

The hormones produced by the thyroid gland are required for energy production. This means that low levels of thyroid hormones can lead to impair energy levels throughout the entire body, including the gut.

This is why many people with Hashimoto’s thyroiditis can also experience gut symptoms such as IBS.  This is often due to slow transit time/constipation. Changes in the composition of bile can also lead to bile stone formation.  [Source: Pubmed]. This is reinforced in studies indicating a higher rate of removal of a gallbladder removal in those with Hashimoto’s [Source: Pubmed].

Additionally, gut bacteria influence the levels of key nutrients required for thyroid health and thyroid hormone conversion. These include iron, iodine, copper, selenium, zinc and vitamin D.

This connection between the gut and the thyroid is termed the thyroid-gut axis and has led to studies being carried out on the use of probiotic supplements to support thyroid health. [Source: Pubmed]

Is there a connection between Hashimotos and IBS?

Imbalances in gut bacteria have also been noted in those with an underactive thyroid which can contribute to the ongoing gut issues in these patients. SIBO (bacterial overgrowth in the small intestine) has been found in more than 50% of those with an underactive thyroid. [Source: Pubmed]

Studies have indicated that dysbiosis (imbalances in the gut bacteria) can increase intestinal permeability (leaky gut) and lead to increased inflammation which can then impact thyroid function. [Source: Pubmed]

Addressing SIBO and thyroid imbalance often needs to be addressed at the same time. This is due to gut issues and microbiome imbalances potentially impacting thyroid health while at the same time, the thyroid imbalances impacting gut health.  This creates a feedback loop or vicious cycle. [Source: Pubmed]

SIBO and constipation

Methane SIBO type of overgrowth where the organisms that have overgrown produce methane gas. This is highly associated with constipation. This is due to the ability of methane to impact the ability of the muscles in the gut to contract leading to slow bowel motility. [Source: Pubmed]

The term methane SIBO has also been questioned as it may not be the appropriate way to name this condition. This is primarily due to SIBO referring to bacterial overgrowth and the methane-producing organisms within the gut belonging to the archaea family, which technically speaking are not bacteria. While these were originally defined as bacteria they are now considered separate.

This has led to the use of the term intestinal methane overgrowth (IMO) rather than the use of the term methane SIBO or methane dominant SIBO. However, as will be mentioned below, it is also possible for certain bacterial species to produce methane. Therefore, it may be more accurate to describe the condition as methane SIBO if bacteria as responsible for the elevated levels of methane and to use IMO when archaea are responsible.

The main methane-producing organism in the digestive tract has been identified as Methanobrevibacter smithii. is not possible to assess for the presence of this organism in a SIBO breath test, however, a microbiome analysis can help to identify its presence. with the gut microbiome. [Source: PubmedPubmed]

Methaninobrevibacter smithii is followed by Methanospaera stadmagnae as the second methane producer. The methanogen Methannobrevibacter oralis is present in the oral cavity which is linked to periodontal disease. [Source: Pubmed]

It has also been shown that bacterial species such as Clostridium and Bacteroides also have the ability to produce methane. As mentioned, a microbiome analysis may help to identify which of these organisms is responsible or contributing to the methane levels. [Source: Pubmed]

Thyroid health and constipation

With one of the most common symptoms of an underactive thyroid gland being constipation, there is a strong relationship between the health of the thyroid gland and gut health. Working to support one also helps to support the other.

As described in this article, there are many possible reasons for symptoms as well as ways to approach these issues. Working with a registered nutritional therapist and gut health practitioner can help to guide this process to restore your gut health.