How Your Gut Microbiota Affects Your Thyroid

Your gut microbiota has an intimate connection with your thyroid including connections with hypothyroidism, Hashimoto’s disease and Graves’ disease. In this research review I’d like to cover a recent paper entitled, “Microbiota and Thyroid Interaction in Health and Disease” published in the journal Trends in Endocrinology and Metabolism by Eleonare Frohlich and Richard Wahl.

The authors begin by stating that the gut microbiota can act on thyroid function due to the region of where someones lives, their diet including iodine intake, obesity, age, sex hormones, and how autoimmunity can impact the microbiota. I was impressed to see them state that the gut microbiota is linked to autoimmune disease, estrogen, iodine, and obesity. Estrogen can be a key factor in Hashimoto’s disease and a healthy gut is required for optimal estrogen metabolism and excretion through the feces.

They also mention the connection between the gut and the liver in relation to thyroid hormone metabolism in both these organ systems. Your gut is key to properly absorbing and utilizing the thyroid medication that you’re taking and they mention this as well.

How Your Gut Microbiota Affects Your Thyroid

Your Gut Microbiota and Hashimoto’s Disease

Thyroid hormone is a vital part of a healthy gut barrier and a healthy gut barrier is vital for Hashimoto’s disease. When the gut microbiota become out of balance, the chances of developing Hashimoto’s disease increases.

The author’s make a very important point that the severity of Hashimoto’s disease is not correlated with the levels of thyroid antibodies such thyroid peroxidase and anti-thyroglobulin. I’ve written about this before that it is unwise to chase antibody levels and get them as low as possible because there is no evidence that lower levels improve Hashimoto’s disease.

The microbiota of patients with Hashimoto’s disease tends to be more diverse and the authors state that this is probably due to slower transit time due to hypothyroidism. I have written about this previously in my Hashimoto’s and SIBO connection article. It’s important to understand that increased diversity of the gut microbiota may be are harmful or beneficial depending on the individual so it isn’t always a good thing to increase diversity.

Interestingly, the authors also state that supplementation with Lactobacillus reuterii improved thyroid function in mice by increasing T4 levels. And when chickens were given lactic acid producing bacteria they had higher T3 levels. We are uncertain if this would also happen in humans however.

As women enter perimenopause, their progesterone levels drop more than estrogen leading to estrogen dominance. Estrogen dominance will have a negative effect on the microbiota but an imbalance microbiota will negatively affect estrogen metabolism and clearance. One of the reasons why some women go through menopause much more smoothly than others is due to the fact that they enter this process with a healthier gut. Increasing estrogen levels can drive autoimmunity so one of the main key factors in Hashimoto’s disease is to focus on a healthy gut so estrogen is in proper balance.

Thyroid medications like levothyroxine may not be absorbed well if there is dysbiosis or small intestinal bacterial overgrowth. Hypothyroidism leads to lower stomach acid levels which can decrease absorption of the medication as well as begin to cause overgrowth and dysbiosis in the the small bowel. Helicobacter pylori infection in the stomach can lower hydrochloric acid levels thus impairing absorption of medication as well. And we know that there is a connection between H. pylori and Hashimoto’s disease.

What about iodine?

Iodine is absorbed in the stomach and upper small bowel but it can be inhibited by inflammation in these areas due to H. pylori, food sensitivities like gluten, and dysbiosis. Fluoride will interfere with absorption of iodine in these areas so be sure you’re filtering your water if it contains fluoride.

Selenium, Iron, Zinc and the Thyroid

The authors point out that these three minerals are vital for proper thyroid function. The thyroid contains more selenium per mg than any other tissue in the body. Selenium is also important for the conversion of T4 to T3. Interestingly, your gut microbiota competes with you for utilization of selenium. You’ll only absorb what gets past your gut bacteria and what they don’t use themselves.

Zinc deficiency has been shown to cause a 30% decrease in T4 and T3 levels. Hypothyroidism causes zinc deficiency and zinc deficiency causes hypothyroidism. Zinc is required for the conversion of T4 to T3 as well. Zinc supplementation inhibits diarrhea and it also promotes the growth of Lactobacillus which can be beneficial.

Iron is required for the production of thyroid hormone in the thyroid gland. Iron is also required for the utilization of T3 in the cell. Iron does decrease microbial diversity which can be a good or bad thing depending in the individual as mentioned above. You must have healthy stomach acid levels to absorb iron which happens primarily in the small intestine.

Another fascinating statement in this paper is that gut bacteria can act as a reservoir for T3 levels thus decreasing the need for T4 medications and also this can prevent fluctuations in thyroid hormone levels. In fact, a study was done on the commercial probiotic product VSL #3 which resulted in fewer thyroid medication dose adjustments compared to those who didn’t take this probiotic.

Your gut microbiota even regulates your neurotransmitters including dopamine which inhibits TSH production. They even interact with your hypothalamic-pituitary-adrenal axis (HPA axis) which is intimately connected to your thyroid through the production of cortisol and adrenaline.

The Link Between Your Gut and Thyroid Disorders

The authors state that the gut-thyroid connection was actually discussed in the 1950’s using the term “thyrogastric syndrome.” Your gut and your thyroid actually come from the same embryonic tissue, in fact the thyroid actually develops from primitive gut cells!

Author Conclusions

There is a connection between altered gut microbiota and Hashimoto’s disease as well as Graves’ disease and hypothyroidism. Key points:

  • The microbiota influences the uptake of iodine in the intestine as well as utilization in the liver.
  • The microbiota influences selenium, iron, and zinc which are vital for thyroid health.
  • The microbiota influences absorption and utilization of thyroid medications.
  • Probiotics may be a useful therapy for thyroid disease.

We don’t know for certain at this point if there is a single direct connection between microbiota imbalances and autoimmune thyroid diseases.

Dr. Hedberg’s Comments

This paper is a real gem with some many excellent key statements. It does a great job tying together the connection between the gut microbiota and the thyroid. I was impressed to see them discuss minerals like zinc, iron, and selenium as well as key points about absorption of thyroid medication, iodine, the HPA-axis, estrogen, and they even mentioned leaky gut.

If anything, this review should be a strong reminder of how important it is to focus on gut health if you have hypothyroidism, Hashimoto’s disease, or Graves’ disease. Be sure you work with a functional medicine practitioner who truly understands the gut-thyroid connection like Dr. Hedberg so you can get well and stay well.

Healing Hashimoto’s is within your reach.

Get started with our free ebook today.