Is Your Thyroid the cause of your SIBO?

Is Your Thyroid Causing Your SIBO?

Who here has thought about their thyroid lately? Probably not many of us! But if you have SIBO, you definitely should. It could be your underactive thyroid causing your SIBO.

I’ve had thyroid issues since right around when I developed SIBO, ten years ago. However, I only recently realized the connection between my thyroid and SIBO. I didn’t think much about it before because, although I have hypothyroidism (meaning my thyroid is lazy and isn’t making enough hormone), it’s been well controlled with medication for years.

However, a while ago I learned that low thyroid function is one of the leading causes of SIBO!

While I’m pretty sure my SIBO was caused by an autoimmune reaction to food poisoning, I developed hypothyroidism the same year that I got SIBO. I can’t help but think there must be some connection there.

If you haven’t figured out what the root of your SIBO is, it could be your thyroid causing your SIBO!

Is your thyroid causing your SIBO?

What is the Thyroid and why is it important?

Basically, the thyroid is a butterfly-shaped endocrine gland at the base of the front of your neck. If you place your fingers to either side above the dip where your neck meets your collarbone, that’s where it is.

thyroid gland SIBO

Why are thyroids so important? The thyroid produces hormones that control your body’s metabolism. This includes how fast food leaves the stomach, enters the intestines, and moves through the intestines (known as transit time). The thyroid also controls other critical functions like the peripheral nervous system, temperature regulation, muscle strength, heart rate, and more.

Symptoms of an under or overactive thyroid

That’s why a malfunctioning thyroid throws your entire body into chaos. I remember that before I got treated, I found myself freezing in normal temperatures, extremely exhausted, weak, and with major brain fog. I knew something wasn’t quite right. Fortunately, my mom and my aunt (a nurse) suggested I get my thyroid levels checked.

Other symptoms of hypothyroidism can include losing your hair, dry skin, constipation, slowed heart rate, depression or sadness, a puffy face, weight gain, and irregular periods.

Hyperthyroidism occurs when the thyroid becomes overactive and makes too much hormone. Many of the symptoms of hyperthyroidism are the opposite of hypothyroidism, which makes sense. This means you might have weight loss, a feeling of anxiety or jitters, diarrhea, overheating or sweating, trouble sleeping (read my post about insomnia and SIBO here), as well as irregular periods and fatigue.

In some unusual cases your thyroid might feel enlarged, or you might see a lump on one side of your neck. While it could be a symptom of hyper or hypothyroidism, it could be a sign of thyroid cancer as well. So if you notice that, please see an endocrinologist ASAP!

Why does an underactive thyroid cause SIBO?

So, how can hypothyrodism lead to SIBO?

The thyroid controls the speed of your digestive system. This includes the migrating motor complex, which is the system that sends electrical impulses to the smooth muscle of the intestines which tell it to sweep bacteria from the small to the large intestine where it belongs.

Because the digestive system becomes consistently sluggish when the thyroid isn’t producing enough hormone, this can cause SIBO because the intestines aren’t sweeping the bacteria from the small intestine into the large one.

Although it might sound like hypothyroidism only causes SIBO with constipation, that isn’t true. SIBO caused by the thyroid can manifest with both diarrhea and/or constipation. Super fun, right?

If you have an overactive thyroid (hyperthyroidism), this doesn’t appear to contribute to SIBO that I can tell. Hyperthyroidism causes the digestive system to speed up. So while hyperthyroidism can cause diarrhea it doesn’t stem from the same reason that SIBO causes diarrhea.

What can you do if this is the cause of your SIBO?

First, if you are still trying to figure out what’s causing your SIBO, get those thyroid levels checked! Any general practitioner or endocrinologist can order the blood test.

If your thyroid levels are off, your doctor will probably prescribe you synthetic T4. Usually the drug is called Synthroid or the generic form of Levothyroxine. Some people also take synthetic T3 because they don’t feel energetic enough on just T4. Some people also take a natural form of thyroid hormone, called Armour. It’s made from desiccated cow or pig thyroid glands. I myself take Levothyroxine.

The big question is, will correcting your thyroid levels cure your SIBO?

Unfortunately, one study on the association between hypothyroidism and SIBO found that over fifty percent of hypothyroid patients that already had corrected their thyroid levels tested positive for SIBO. That seems to indicate that it isn’t enough to fix thyroid levels and expect your SIBO will clear itself.

More likely the right course of action is to clear your bacteria using pharmaceutical or herbal antibiotics (read my guide to treating SIBO with herbal antibiotics here). At the same time, make sure your thyroid hormone levels have been corrected.

You can read about how I treated my SIBO here.

Some final thoughts…

What’s interesting to me is that it seems an underactive thyroid must be a pretty common cause of SIBO. One study found that, when they tested a group of hypothyroid patients for SIBO, over fifty percent of them had SIBO!

I definitely wonder if my thyroid a factor for me, because I developed hypothyroidism after SIBO. But, it seems like it should be the other way around–thyroid first, then SIBO. It’s possible that the combination of the autoimmune reaction to food poisoning I had plus my lazy thyroid both contributed.

But, I haven’t really heard a lot of patients talking about their thyroid causing SIBO. If your thyroid caused your SIBO, I would love to hear your experience in the comments. Did balancing your thyroid hormones help? What do you take for it?





  1. I had never heard of this connection, and definitely think it applies to me. I’m going to look further into it. I was undermedicated for years (thyroid dose of armour and/or t3 too low), and then overmedicated (during which time my bloating issues reduced significantly), and last few years undermedicated again (and interestingly my bloating issues returned). Thank you!

    1. Yes, definitely something worth researching more for you it sounds like! It can be really hard to get the dosages right. Best of luck and I hope you have a good endocrinologist you’re working with.

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