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.

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,