Is There a Link Between IBS and Thyroid Disease?

If you have thyroid disease as well as irritable bowel syndrome (IBS), it's understandable to wonder if there's a connection between the two. Although there are numerous health problems that IBS patients experience at a higher rate than others, there's no evidence that having thyroid disease causes IBS or vice versa. That said, thyroid disease can cause similar gastrointestinal symptoms to those of IBS, so it can be easy to conflate them.

Your thyroid gland is responsible for releasing hormones that affect the way cells work throughout your body. When the thyroid is not functioning properly, this release of hormones is either excessive, resulting in hyperthyroidism, or deficient, resulting in hypothyroidism. As these hormones are involved in metabolism and digestion, a problem with the thyroid can result in gastrointestinal (GI) symptoms.

When hormone levels are high, as in Graves' disease (the most common form of hyperthyroidism), intestinal motility is increased and the lining of the intestine may secrete more fluids, resulting in symptoms such as:

• Diarrhea
• Indigestion (dyspepsia)
• Increased appetite
• Fat malabsorption

With hypothyroidism, the action of the gut is slowed, leading to:

• Constipation
• Less frequent bowel movements
• Abdominal discomfort and bloating
• Bouts of diarrhea

Small intestinal bacterial overgrowth, known as SIBO, occurs when excessive amounts of gut bacteria accumulate in the small intestine and cause symptoms such as bloating, constipation, and diarrhea. Hypothyroidism and IBS are two of the conditions associated with SIBO, as both can result in decreased intestinal motility. This essentially causes the bacteria to "back up" instead of being released during the normal digestive process.

While the relationship between IBS and SIBO is not clear—and is, in fact, controversial—a 2014 review of the literature concluded that SIBO may be present in as many as 50 percent of people with hypothyroidism.

Because GI symptoms in IBS and thyroid disease often overlap, it can be tricky to determine the underlying cause. As part of the routine diagnostic workup for IBS, it's essential that your doctor rule out the presence of thyroid abnormalities; this can be done via a simple blood test.

Getting proper treatment for thyroid disease should help relieve your related digestive symptoms, but it will not relieve symptoms caused by IBS. Make sure to work with your doctors to get to the bottom of which condition is causing which symptoms so you can get an appropriate diagnosis and effective treatment.