Can SIBO Cause Thyroid Autoimmunity?

Being hypothyroid or on thyroid medication has been shown to significantly enhance your risk of SIBO.  But could it be that it’s actually the SIBO that is driving the thyroid problem? Let’s discuss how SIBO may contribute to thyroid autoimmunity.

Clinicians – for a detailed write-up on the gut-thyroid connection, see

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Can SIBO Cause Thyroid Autoimmunity?

Dr. Michael Ruscio: Hi, this is Dr. Ruscio. And let’s discuss if SIBO, or small intestinal bacterial overgrowth, could actually cause thyroid autoimmunity. And just quickly, thyroid autoimmunity, also known as Hashimoto’s, is the main cause of thyroid autoimmunity in Westernized countries. So it’s definitely an important underlying factor in hypothyroidism and thyroid disease.

We’re learning more and more about the importance of the gut and how that connects to the immune system, most namely in this case, how it connects to the thyroid. And there is some preliminary evidence, most notably in the treatment of H. pylori bacterial infections in the stomach being shown to have the ability to help improve thyroid autoimmunity. So there could definitely be a connection here.

Now, other studies have shown us that one of the strongest predictors of if someone will have SIBO is if they have hypothyroid or if they are on thyroid medication. So we definitely know that hypothyroidism and SIBO tend to have some overlap. The question is, could the SIBO actually be causing the thyroid autoimmunity? And while this is speculative, I think it’s interesting and something that we could all benefit from understanding.

Some evidence has shown that intestinal bacteria actually utilize selenium. And if these bacteria overgrow, there may be an increased demand for selenium in the gut by these bacteria as they’re eating the selenium. That may cause a selenium deficiency in the host, in the person who has the SIBO. And selenium deficiencies have been documented to be one of the underlying factors that contributes to thyroid autoimmunity. This is why we see some trials showing that when people who have thyroid autoimmunity take supplemental selenium, we see an improvement in the thyroid autoimmunity.

So, again, the reason why we see SIBO and hypothyroid and thyroid autoimmunity go hand in hand may be because bacterial overgrowths are present. Those bacterial overgrowths utilize more of your selenium, creating a slight selenium deficiency. And that selenium deficiency has been shown to underlie thyroid autoimmunity.

Now, one question that comes up is, if intestinal bacteria can feed on selenium, would giving selenium cause or contribute to or exacerbate a bacterial overgrowth? Most likely not, because in the clinical trials where we give patients selenium, I have not seen any notable adverse reactions reported that would indicate that the SIBO is overgrowing, meaning gas, constipation, diarrhea, abdominal pain, what have you. So, most likely, if someone has SIBO and thyroid autoimmunity, a trial of selenium would be a safe bet for them.

So in recap, we know that thyroid autoimmunity is the main driver of hypothyroidism. We also know that thyroid autoimmunity and small intestinal bacterial overgrowth tend to go hand in hand in many cases. And what may happen and what may contribute to that in part is, overgrowth of bacteria utilizes your selenium, this utilization of selenium may create a subtle deficiency, and that may contribute to thyroid autoimmunity.

So what this means is if you have thyroid autoimmunity, you should look to your gut health as an important part of the process for improving your immune system and improving the status of your thyroid autoimmunity. Also remember that many times, the symptoms that we think are hypothyroid or coming from hypothyroid are actually coming from the gut. So the gut is a crucial part of the successful management of hypothyroidism and thyroid autoimmunity.

This is Dr. Ruscio. And I hope this information helps you get healthy and get back to your life. Thank you.

If you need help with SIBO or thyroid autoimmunity, click here.
To be notified when my print book becomes available & get a free gut health eBook, click here.
If you are a healthcare provider looking to sharpen your clinical skills, click here.

What do you think? I would like to hear your thoughts or experience with this.

Dr. Ruscio is your leading functional and integrative doctor specializing in gut related disorders such as SIBO, leaky gut, Celiac, IBS and in thyroid disorders such as hypothyroid and hyperthyroid. For more information on how to become a patient, please contact our office. Serving the San Francisco bay area and distance patients via phone and Skype.


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