The digestive system is a complex part of human biology that the body uses to break down food and provide our cells with the energy and nutrients they need to function. Though what we eat and drink is of major importance to how the digestive system functions, there are also many other factors that have an impact. The thyroid gland is an example of another factor that affects digestion, even though it isn’t technically part of the digestive system. Through the hormones it releases, the thyroid regulates numerous aspects of human health, including metabolism and digestion. This is also why problems like thyroid disease can cause gastrointestinal symptoms.
How Does the Thyroid Function?
The thyroid gland is a butterfly-shaped gland located in the lower front part of the neck next to the trachea, and it responds to the release of TSH (thyroid-stimulating hormone) that is released by the pituitary gland. As an endocrine organ, the thyroid works by secreting hormones directly into the bloodstream where they are carried around the body. Thyroid hormone works as a messaging system that the body uses to regulate a wide variety of functions like heart rate, breathing, body temperature, cholesterol, menstrual cycles in women, weight and metabolism.
Thyroid Disease: Hyperthyroidism vs Hypothyroidism
Because thyroid hormone is so versatile and important, the amount that is released into the bloodstream is crucial for maintaining normal health. Thyroid disease is characterized by dysfunction of the thyroid, and the two most common types are related to the production of thyroid hormone. When the body produces more thyroid hormone than is needed, this is called hyperthyroidism; when the body produces less thyroid hormone than needed, it is called hypothyroidism. Both conditions are considered a health problem and typically cause a number of symptoms:
Symptoms of Hyperthyroidism
- increased sensitivity to heat
- increased heart rate
- nervousness or anxiety
- hand tremors
- difficulty sleeping
- muscle weakness
- weight loss
- increased appetite
- menstrual cycle changes
- goiter (visibly enlarged thyroid gland)
Symptoms of Hypothyroidism
- increased sensitivity to cold
- reduced heart rate
- fatigue or weakness
- joint or muscle pain
- weight gain
- dry or coarse skin
- heavier menstrual periods
- paleness of the skin
It is estimated that approximately 20 million Americans suffer from some form of thyroid disease, though many don’t even realize they have it. Many people dismiss the symptoms as indicative of other conditions, and they don’t get checked out by a healthcare professional. For reasons that aren’t fully understood, women are eight times more likely to develop a thyroid disorder than men. Moreover, undiagnosed thyroid disorders increase the risk for more serious conditions like heart disease, infertility, and osteoporosis.
How Does the Thyroid Affect the Digestive System?
Though the symptoms associated with thyroid disease may be different for different people, in general hyperthyroidism tends to cause diarrhea and hypothyroidism tends to cause constipation. This is because the amount of thyroid hormone in the body has a direct impact on the speed of metabolism and bowel motility. Under normal circumstances, digested food moves into the colon and a sufficient amount of water is absorbed so that the stool that forms is solid but still relatively soft and easy to pass.
In cases of hyperthyroidism, the process is sped up and stool moves through the colon too quickly, before enough water is absorbed. This results in loose or watery stools; this is typically considered diarrhea when it occurs three or more times a day. Conversely, in cases of hypothyroidism, the process is slowed down and too much water is absorbed because the stool remains in the colon too long. This leads to hard, dry stools that are difficult to pass; it is typically considered constipation when a person has fewer than three bowel movements in a week.
Another way the thyroid gland can indirectly affect the gastrointestinal system is through the gut microbiome. Having too much or too little thyroid hormone in the body can cause an imbalance in the amount and diversity of gut bacteria in the intestines; recent research has shown a link between microbiome imbalance and problems with immune system health, among others. This has been known to lead to thyroid related autoimmune conditions like Hashimoto's thyroiditis and Graves' disease, two diseases that can cause an enlarged thyroid gland and a host of additional symptoms and complications.
How to Treat Thyroid-Related Digestion Problems
One of the challenges of having a thyroid problem is that it’s difficult to know the underlying cause. Once hyperthyroidism or hypothyroidism are diagnosed, however, the standard treatment involves returning thyroid hormone levels to normal. If the problem is too much thyroid hormone, antithyroid medications like methimazole and propylthiouracil may be prescribed; if the problem is an underactive thyroid gland, thyroid replacement medication like levothyroxine can be prescribed to fill in the gap. In severe cases of overactive thyroid, surgery (thyroidectomy) may be necessary; in such cases thyroid hormone replacement medication will be required for the rest of the patient’s life.
Other Ways to Improve Gut Health
For some people, thyroid problems may be causing gastrointestinal symptoms and negatively affecting gut health; for other people, the reverse may be true. Research into the connection between thyroid and the microbiome is ongoing, but there are some tips for improving gut health that may also have a positive impact on thyroid function:
- Stay hydrated: drinking sufficient water is important in general for digestive health because it helps maintain regular bowel motility
- Eat vegetables: the fiber content of vegetables is highly beneficial for digestion and the formation and passage of regular stools
- Probiotics: though more research is needed, there is evidence that fermented probiotic foods like yogurt and sauerkraut have a positive effect on gut bacteria
- Increase physical activity: exercise and physical movement in general is good for overall health and digestive health
Be Proactive With Your Gastrointestinal Health
The truth is that many people have thyroid problems and don’t even know it. If you have been experiencing recurrent diarrhea or constipation—or any other gastrointestinal symptoms—you may benefit from talking with a gastroenterologist. At Cary Gastro, we are passionate about providing excellent digestive healthcare so that you can improve your quality of life. To speak with someone about your symptoms, please contact us today to request an appointment.