Gut Health Series, Part 2: The Gut-Thyroid Connection
Did you know the most common cause of hypothyroidism in the US is not an iodine deficiency, but an autoimmune condition? Over 90% of hypothyroid cases in this country are caused by Hashimoto’s, or autoimmune thyroid. Hashimoto’s occurs when the immune system becomes overactive and launches an attack on the thyroid gland. These immune attacks can damage the thyroid, reducing its ability to produce hormones and causing symptoms of hypo, or low, thyroid function. Symptoms of hypothyroid include fatigue, dry skin, hair loss, constipation, and weight gain. These immune attacks can also cause too much thyroid hormone to spill into the blood stream, causing hyperthyroid symptoms like heart palpitations, weight loss, anxiety, and insomnia. Many Hashimoto’s patients experience “swings” between hypo and hyperthyroid symptoms. Levels of TSH, the most common lab used to measure thyroid function, will often fluctuate, leading to frequent changes in medication dosages but no symptom relief.
This common approach of “chasing” TSH levels and constantly adjusting doses of thyroid medication is often ineffective. This is because it does not address the root cause, which is dysfunction in the immune system. Poor gut health may be the biggest contributor to thyroid problems because around 80% of the immune system is located in the gut! A healthy gut and balanced immune system are absolutely essential for thyroid health. Conversely, getting your thyroid back in working order improves digestion, as thyroid hormones help control gut function.
How exactly are the gut and thyroid connected?
The thyroid gland produces two thyroid hormones: T4 (thyroxine) and T3 (triiodothyronine). 80% of hormone produced by the thyroid is T4 and twenty percent is T3. T4 is “inactive” while T3 is the “active” version utilized by your cells to regulate energy, metabolism and many other functions. T4 must be converted into T3, a process that occurs primarily in the gut and liver. So digestive health is key to producing enough “active,” or usable, thyroid hormone.
There are a number of factors that can compromise digestive health, including antibiotics, NSAIDs, birth control pills, chronic stress, and poor diet. These create inflammation in the gut and a breakdown of the protective barrier lining your small intestine, a condition known as “leaky gut.” This allows undigested proteins, bacteria, and other particles to “leak” into the bloodstream where they don’t belong. The immune system does not recognize these particles and flags them as “invaders,” launching an attack. This can cause an increase in food allergies/sensitivities, but also poses a risk to body tissues, such as your thyroid. When the immune system becomes overactive, it starts to attack proteins that looks alike, a process called molecular mimicry. Certain proteins found in food, for example gluten or dairy, look similar to proteins found in your thyroid gland. Once you develop a sensitivity to a food, your immune system may also go after the look-alike proteins in your thyroid. This cascade is an example of the close connection between gut and thyroid health- if one is off, the other can not function properly and a vicious cycle begins.
As discussed in the first article of this series, the gut also communicates with the brain. An imbalance of bacteria in the gut, known as dysbiosis, can trigger an inflammatory response throughout your entire body. Over time, inflammation lights a fire in the brain and decreases TSH (thyroid stimulating hormone), which controls production of thyroid hormones. Low TSH equals low thyroid hormones, resulting in hypothyroid symptoms.
Gut health is also important for proper production of T3- the active form of thyroid hormone. Remember, your thyroid produces mostly T4, which is inactive. 20% of your T4 is converted to the active T3 form by bacteria in the gut. In addition to converting T4 to T3, the gut is also responsible for absorbing the building blocks of thyroid hormones, including iodine, iron, selenium, zinc, copper, and B vitamins.
Just like the gut controls the thyroid, the thyroid controls the gut!
Hypothyroidism can lead to hypochlorhydria, or low levels of stomach acid. Stomach acid is the first step in digesting proteins and also kills of harmful food borne bacteria. When it’s low, food passes into the small intestine undigested and potentially full of bacteria, leading to poor digestion, inflammation, and possible infection.
Hypothyroidism can also cause the gallbladder to become sluggish and congested. The gallbladder secretes a substance called bile, which helps break down fats. When the gallbladder is compromised, you don’t break down fats and hormone production suffers (you need dietary fat to make cholesterol, the backbone of hormones). A sluggish gallbladder also affects liver function and detoxification- remember that the majority of T4 to T3 conversion, up to 60%, occurs in the liver. Poor liver detoxification can also cause high estrogen levels. High estrogen increases a protein that binds to thyroid hormone in the bloodstream. These bound hormones are essentially inactive, as they can not be used by cells. This is why many people show “normal” levels of thyroid hormones on tests, but are still symptomatic.
What if I don’t have digestive symptoms?
Keep in mind that you do not have to have digestive symptoms to have poor gut health!
People with serious gut issues may or may not have symptoms. Even Celiac disease, an autoimmune disease that destroys the small intestine, can be “silent,” meaning those affected don’t complain of digestive symptoms. In many people, gut conditions can present in seemingly unrelated symptoms such as headaches, fatigue, sinus congestion, depression, mood swings, rashes, or skin outbreaks.
What can I do to improve gut health and support my thyroid?
Focus on fresh foods. Minerals like iodine, zinc, selenium are vital for thyroid hormone production- they are also seriously lacking in most processed foods. Eating antioxidant rich fruits and vegetables also helps to lower inflammation, which can stress the thyroid.
Support detoxification. Thyroid hormone conversion (the process used to make the hormone “active”) occurs mainly in the liver. If the liver is stressed due to poor diet, alcohol, or exposure to toxins, mold or heavy metals, this process slows down. Drinking plenty of water and adding leafy greens and cruciferous vegetables (kale, cabbage, broccoli, cauliflower, Brussels sprouts) help support healthy detoxification.
Add a probiotic supplement. Adding a quality probiotic is one of the best ways to increase levels of healthy bacteria in the gut. Remember, these bacteria help convert inactive thyroid hormones into their active form!
Consider cutting out gluten and dairy. Gluten and dairy are some of the most common food sensitivities and can cause inflammation in the gut. Their proteins also look similar to proteins found in the thyroid gland, and can worsen symptoms in people with Hashimoto’s or other autoimmune conditions.