Can Hypothyroidism Cause Diarrhea?

11 min readSep 22, 2023

Hypothyroidism is a common endocrine disorder that affects millions of people worldwide. Characterized by an underactive thyroid gland, this condition leads to a variety of symptoms, including fatigue, weight gain, and cold intolerance. However, while many are aware of the more typical symptoms of hypothyroidism, there’s often confusion and curiosity surrounding less common symptoms, such as diarrhea. Can hypothyroidism cause diarrhea?

This article delves into the intricate relationship between hypothyroidism and gastrointestinal issues to provide a comprehensive understanding of the topic.

The Thyroid Gland and Its Functions

Before delving into the connection between hypothyroidism and diarrhea, it’s crucial to comprehend the thyroid gland’s role in the body. The thyroid gland, a butterfly-shaped organ located in the neck, is responsible for producing hormones that regulate metabolism.

These hormones, primarily thyroxine (T4) and triiodothyronine (T3) influence various bodily functions, including:

Metabolism: Thyroid hormones play a central role in regulating the body’s metabolic rate. They affect how the body converts food into energy, impacting weight management and overall energy levels.
Heart Rate: Thyroid hormones influence the heart rate and rhythm, ensuring proper cardiovascular function.
Temperature Regulation: They help maintain body temperature by affecting how the body generates and conserves heat.
Brain Function: Thyroid hormones are essential for brain development in infants and cognitive function in adults.
Muscle Function: These hormones affect muscle strength and coordination.
Digestive Function: Thyroid hormones influence the speed at which food moves through the digestive tract, impacting digestion and nutrient absorption.

Hypothyroidism: A Brief Overview

Hypothyroidism occurs when the thyroid gland fails to produce an adequate amount of thyroid hormones. This deficiency disrupts the body’s normal functions, leading to a range of symptoms. The most common signs and symptoms of hypothyroidism include:

Fatigue: Individuals with hypothyroidism often experience extreme tiredness, even after a full night’s sleep.
Weight Gain: A slower metabolism caused by inadequate thyroid hormones can lead to weight gain or difficulty losing weight.
Cold Sensitivity: Hypothyroidism can make individuals more sensitive to cold temperatures.
Dry Skin and Hair: Skin may become dry and hair brittle.
Depression and Mood Changes: Changes in thyroid hormone levels can affect mood and may lead to symptoms of depression.
Muscle Weakness: Muscle weakness and pain are common in individuals with hypothyroidism.
Constipation: Sluggish digestion often results in constipation.

These are some of the well-recognized symptoms, but it’s important to note that the presentation of hypothyroidism can vary from person to person. Additionally, some individuals may experience less common symptoms, such as diarrhea.

Hypothyroidism and Diarrhea: The Connection

The relationship between hypothyroidism and diarrhea is complex and not fully understood. While diarrhea is not a classic symptom of hypothyroidism, some individuals with this condition do experience it. Several mechanisms may explain this connection:

1. Gastrointestinal Motility:

Gastrointestinal motility refers to the coordinated muscular contractions that propel food and waste products through the digestive system. This process is crucial for the efficient digestion and absorption of nutrients while ensuring the elimination of waste. The muscles in the walls of the digestive tract contract rhythmically, pushing food and its byproducts along the gastrointestinal (GI) tract.

In individuals with hypothyroidism, the reduced production of thyroid hormones can have a notable impact on gastrointestinal motility. Thyroid hormones play a vital role in regulating the speed and intensity of these muscular contractions. When thyroid hormone levels are insufficient, as is the case in hypothyroidism, several changes can occur:

Slower Transit Time: Hypothyroidism often leads to slower GI transit times. This means that food and waste products move through the digestive tract at a sluggish pace. Slower transit times are more commonly associated with constipation, a hallmark symptom of hypothyroidism.
Irregular Contractions: In some instances, hypothyroidism can disrupt the normal pattern of muscular contractions in the digestive tract. Instead of coordinated, rhythmic contractions, irregular and uncoordinated movements may occur. These irregular contractions can lead to a condition known as “spastic colon” or irritable bowel syndrome (IBS), which is characterized by diarrhea as one of its primary symptoms.
Altered Secretions: Thyroid hormones also influence the secretion of digestive enzymes and fluids in the GI tract. Reduced thyroid hormone levels can lead to changes in these secretions, potentially affecting digestion and bowel movements.

The net result of these motility-related changes can manifest as a wide spectrum of GI symptoms, including diarrhea in some individuals. While hypothyroidism typically leans towards causing constipation due to its inhibitory effects on motility, the complex interplay of factors within the digestive system can lead to variations in how individuals experience GI symptoms.

It’s important to note that the impact of hypothyroidism on gastrointestinal motility can vary from person to person. Factors such as the severity of hypothyroidism, individual physiology, and the presence of other coexisting GI conditions can all influence the likelihood and nature of GI symptoms, including diarrhea.

2. Malabsorption:

Malabsorption is a term used to describe the inadequate absorption of nutrients from the gastrointestinal (GI) tract into the bloodstream. This can occur when the normal processes of digestion and absorption are disrupted, leading to a range of nutritional deficiencies and GI symptoms. In the context of hypothyroidism, malabsorption can occur due to several interrelated factors:

Slowed Digestive Processes: Hypothyroidism, characterized by low thyroid hormone levels, often leads to a slowdown in the overall digestive process. This sluggishness can affect the breakdown of food and the release of digestive enzymes, which are essential for the proper absorption of nutrients. As a result, nutrients, including fats and carbohydrates, may not be adequately broken down and absorbed.
Altered Intestinal Lining: Thyroid hormones play a role in maintaining the integrity of the intestinal lining. In hypothyroidism, changes in the structure and function of the intestinal lining can occur. This can lead to a condition known as “leaky gut,” where the intestinal barrier becomes more permeable, allowing substances that should be contained within the intestines to pass into the bloodstream. This increased permeability can contribute to malabsorption and GI symptoms, including diarrhea.
Nutrient Transport: Thyroid hormones also influence the transport of nutrients across the intestinal lining and into the bloodstream. In hypothyroidism, impaired thyroid function can hinder this transport mechanism, further exacerbating malabsorption issues.

Malabsorption can result in a variety of nutritional deficiencies, including deficiencies in fat-soluble vitamins (A, D, E, and K), B vitamins (such as B12), and minerals like iron and calcium. These deficiencies can have widespread effects on the body, including changes in bowel habits.

Here’s how malabsorption can lead to diarrhea:

Fat Malabsorption: Inadequate digestion and absorption of fats can lead to an excess of undigested fats in the GI tract. These fats can have a laxative effect, causing diarrhea, often referred to as “steatorrhea.” Steatorrhea is characterized by foul-smelling, pale, and bulky stools.
Bacterial Overgrowth: Malabsorption can disrupt the balance of bacteria in the GI tract, leading to bacterial overgrowth in the small intestine. This overgrowth can produce excess gas and substances that irritate the gut lining, leading to diarrhea and abdominal discomfort.
Osmotic Diarrhea: Malabsorption of carbohydrates can lead to the presence of undigested sugars in the intestines. These sugars can draw water into the intestines, leading to osmotic diarrhea, which is characterized by watery stools.

It’s important to note that malabsorption in hypothyroidism can be multifactorial, and not all individuals with hypothyroidism will experience diarrhea as a result.

Factors such as the severity of thyroid hormone deficiency, the presence of other gastrointestinal conditions, and individual variations in GI function can influence the likelihood and nature of GI symptoms.

3. Coexisting Conditions:

Hypothyroidism often coexists with other medical conditions, and these concurrent health issues can significantly influence the gastrointestinal tract, potentially leading to diarrhea.

Here are some key coexisting conditions:

Celiac Disease: Individuals with autoimmune thyroid disorders, including hypothyroidism, have an increased risk of celiac disease. Celiac disease can cause damage to the intestinal lining, leading to malabsorption and diarrhea.
Inflammatory Bowel Disease (IBD): Conditions like Crohn’s disease and ulcerative colitis, both forms of IBD, can co-occur with hypothyroidism. Inflammation and immune system involvement in IBD may contribute to diarrhea.
Small Intestinal Bacterial Overgrowth (SIBO): Hypothyroidism can slow gut motility, predisposing individuals to SIBO. SIBO can result in diarrhea due to bacterial interference with nutrient absorption.
Nutritional Deficiencies: Hypothyroidism can disrupt appetite and metabolism, potentially causing nutrient deficiencies that impact the gut and contribute to diarrhea.
Stress and Anxiety: Mood changes in hypothyroidism, such as increased stress and anxiety, can disrupt normal bowel function and lead to diarrhea.
Medication Side Effects: Some medications used to manage hypothyroidism may have gastrointestinal side effects, including diarrhea.

These coexisting conditions emphasize the need for comprehensive evaluation and tailored management to address not only hypothyroidism but also its associated factors when addressing diarrhea in affected individuals.

4. Medications:

Medications used to treat hypothyroidism, such as levothyroxine (Synthroid), are typically well-tolerated by most patients. However, in some cases, these medications can lead to gastrointestinal side effects, including diarrhea.

Here’s how this can happen:

Dosage Adjustment: Determining the correct dosage of thyroid medication is a delicate process. If the dosage is too high or rapidly increased, it can result in hyperthyroidism-like symptoms, including diarrhea. Conversely, if the dosage is too low, hypothyroidism symptoms may persist, which can also include gastrointestinal issues.
Sensitivity to Fillers or Excipients: Some formulations of thyroid medication contain fillers, dyes, or excipients that individuals may be sensitive or allergic to. These additives can potentially irritate the gastrointestinal tract and lead to diarrhea or other digestive disturbances.
Individual Variation: Every individual’s response to medications can vary. While many people with hypothyroidism tolerate thyroid hormone replacement medications well, some may experience gastrointestinal side effects, including diarrhea, as an idiosyncratic reaction.
Interactions with Other Medications: Medications for other conditions taken concurrently with thyroid medications can interact and potentially lead to gastrointestinal symptoms, including diarrhea. This underscores the importance of a comprehensive medication review by healthcare providers.

It’s essential to communicate any new or unusual symptoms, including diarrhea, to your healthcare provider when taking thyroid medications. They can adjust the dosage, switch to a different medication formulation, or evaluate potential interactions with other drugs.

Close monitoring and collaboration with a healthcare professional can help mitigate medication-related gastrointestinal issues and ensure optimal thyroid management for individuals with hypothyroidism.

5. Stress and Anxiety:

Stress and anxiety are complex emotional factors that can exert significant influence over the gastrointestinal system, potentially leading to diarrhea in individuals with hypothyroidism. Here’s a more detailed explanation of this relationship:

Gut-Brain Connection: The gut and brain are intricately connected through the gut-brain axis. This bidirectional communication system allows emotions, such as stress and anxiety, to impact gut function. Stress and anxiety can trigger physiological responses in the gut, including changes in motility, secretion, and sensitivity. In hypothyroidism, where the endocrine system is already disrupted, these emotional factors can further destabilize the balance in the gut.
Altered Gut Motility: Stress and anxiety can accelerate gut motility, leading to increased contractions and faster transit of contents through the digestive tract. In some individuals, this heightened motility can result in diarrhea, characterized by frequent, loose, and watery stools.
Irritable Bowel Syndrome (IBS): Hypothyroidism and stress are both associated with an increased risk of developing irritable bowel syndrome (IBS), a chronic gastrointestinal disorder characterized by abdominal pain, bloating, and diarrhea or constipation. Stress can exacerbate IBS symptoms, making diarrhea more likely in individuals with hypothyroidism.
Hypervigilance: Individuals with hypothyroidism may become hypervigilant about their health due to concerns about their thyroid condition. This heightened awareness can lead to increased stress and anxiety, which, in turn, can further disrupt gastrointestinal function.
Medication Effects: Stress and anxiety can influence medication compliance and absorption. Inconsistent thyroid medication intake due to anxiety or stress-related forgetfulness can result in fluctuating thyroid hormone levels, potentially exacerbating gastrointestinal symptoms, including diarrhea.

Recognizing and addressing stress and anxiety as potential contributors to diarrhea in individuals with hypothyroidism is crucial. Stress management techniques such as mindfulness, relaxation exercises, counseling, and lifestyle adjustments can help mitigate these emotional factors.

6. Autoimmune Factors:

Hypothyroidism can be caused by autoimmune thyroiditis, commonly known as Hashimoto’s disease, where the immune system mistakenly attacks and damages the thyroid gland.

This autoimmune process can extend beyond the thyroid and affect other parts of the body, including the gastrointestinal (GI) system. Here’s a more comprehensive explanation:

Systemic Autoimmune Involvement: Autoimmune thyroiditis, like other autoimmune diseases, can involve systemic immune responses. This means that the autoimmune process isn’t limited to the thyroid gland but can affect various organs, including the GI tract. Inflammation triggered by autoimmune responses can disrupt normal GI function.
Inflammation and Intestinal Permeability: Autoimmune processes can lead to chronic inflammation in the GI tract. This inflammation can damage the lining of the intestines, leading to increased permeability, often referred to as “leaky gut.” A leaky gut allows substances that should remain in the intestines to pass into the bloodstream, potentially triggering immune responses and GI symptoms, including diarrhea.
Antibodies and Cross-Reactivity: Autoimmune thyroiditis is characterized by the production of specific antibodies against thyroid tissue. These antibodies can sometimes cross-react with other tissues, including the gut lining. This molecular mimicry can lead to autoimmune reactions in the GI tract, contributing to diarrhea.
Coexisting Autoimmune Conditions: Individuals with autoimmune thyroiditis are at an increased risk of developing other autoimmune conditions, such as celiac disease, which can cause diarrhea as a primary symptom. The presence of multiple autoimmune conditions can complicate the clinical picture and contribute to GI symptoms.

When to Seek Medical Evaluation

Experiencing diarrhea alongside other symptoms of hypothyroidism should prompt individuals to seek medical evaluation. It’s crucial to differentiate between diarrhea caused by hypothyroidism and other potential underlying causes, such as infections, dietary factors, or gastrointestinal disorders.

A healthcare provider will conduct a thorough evaluation, which may include blood tests to measure thyroid hormone levels (TSH, T4, and T3) and other relevant tests to assess gastrointestinal function. Based on the findings, they can determine the cause of diarrhea and develop an appropriate treatment plan.

Treating Diarrhea in Hypothyroidism

The treatment approach for diarrhea in individuals with hypothyroidism depends on the underlying cause.

Here are some potential strategies:

Optimizing Thyroid Hormone Replacement: If diarrhea is a result of inadequate thyroid hormone replacement therapy, adjusting the dosage of thyroid medication can help resolve the issue. It’s essential for individuals with hypothyroidism to work closely with their healthcare provider to ensure their medication dosage is appropriate.
Managing Coexisting Conditions: If a gastrointestinal condition like celiac disease is contributing to diarrhea, addressing that condition through dietary modifications and other treatments may be necessary.
Stress Management: Managing stress and anxiety, which can exacerbate gastrointestinal symptoms, can be beneficial. Techniques such as mindfulness, meditation, and counseling may help reduce stress levels.
Dietary Changes: In some cases, dietary modifications, such as avoiding certain trigger foods, may help alleviate diarrhea symptoms. Consulting with a registered dietitian can be valuable in creating a suitable dietary plan.
Medication Management: If medications used to treat hypothyroidism are causing diarrhea, a healthcare provider may adjust the medication type or dosage to minimize gastrointestinal side effects.

Conclusion

In conclusion, while diarrhea is not a classic symptom of hypothyroidism, there is a complex and multifaceted relationship between the two. Hypothyroidism can affect gastrointestinal function in various ways, potentially leading to diarrhea in some individuals. Understanding this connection is essential for accurate diagnosis and appropriate management.

If you or someone you know is experiencing diarrhea along with other symptoms of hypothyroidism, it is crucial to seek medical evaluation to determine the underlying cause and receive proper treatment. Effective management often involves optimizing thyroid hormone replacement therapy, addressing coexisting gastrointestinal conditions, managing stress, making dietary adjustments, or modifying medication regimens.

Note: This article is for informational purposes only and should not replace professional medical advice. If you suspect you have Hypothyroidism or any other thyroid condition, please consult with a healthcare professional.