thyroid and your gut

Is there a link? 

Thyroid and gut diseases often co-exist, for example, autoimmune thyroid disease and celiac disease often show up together. We’ve known about this link since the 1950’s but it’s only just starting to gain traction now. 

Gut dysbiosis is often found in those with thyroid disease, like Hashimoto’s thyroiditis and Graves’ disease (more on these below). Poor gut health may impair thyroid function and poor thyroid function can contribute to inflammation and ‘leaky gut’.

Decreases in specific species have been found in those with thyroid conditions, such as hyperthyroid individuals, whereby less bifidobacterial and lactobacillaceae and more enterococcus spp were observed compared to controls. 

What is your thyroid 

Your thyroid is a gland and belongs to your endocrine system. It is butterfly shaped and found on your neck. It is responsible for many bodily functions and produces and secrets thyroid hormones and regulates iodine levels.

Your thyroid produces thyroid hormones, T3 and T4. T4 is inactive and T3 considered active (think of T4 like a teabag, you’ve got to add hot water to make the most out of it).

Thyroid hormones effect how your heart works, basal metabolic rate, respiration, CNS and hormonal health, including the regulation of normal productive function in both men and women. 

Here are a few common thyroid conditions: 

• Hypothyroidism (underactive thyroid) – this is where your thyroid doesn’t produce enough thyroid hormones. 
• Hyperthyroidism (overactive thyroid) – this is where your thyroid produces too many thyroid hormones (3 out of 4 people also have Graves’ disease). 
• Hashimotos Thyroiditis – an autoimmune condition where the immune system attacks your thyroid gland, causing inflammation and damage. Damage to the thyroid ultimately stops your thyroid from being able to produce enough thyroid hormone. 
• Graves’ disease – this is an autoimmune condition where your immune system attacks your thyroid and hyperthyroidism occurs as a result. 

Immune system 

Your gut is home to 70% of your immune system in the form of gut associated lymphoid tissue (or GALT as it is affectionately known). GALT is VERY important and acts like a larder for storing part of your immune system’s defence system, immune cells. Immune cells, like T and B lymphocytes are deployed to defend you against potential threats and in the case of Hashimotos, immune cells attack self.

But what does this mean for thyroid health? We were struggling to see the link too, but let us explain. Your immune system can be triggered through something going on in your gut, take leaky gut (we aren’t just talking the normal leakiness we all get), stuff can get through that shouldn’t and so your body amounts an immune response. If a thyroid condition has your immune system working overtime, this can have a negative effect on your gut health.

Converting hormones into the useful ones 

Some T4 actually gets converted into the active T3 in the gut using an enzyme, intestinal sulfatase which comes from your beneficial microbes! If your gut is out of whack (commonly termed dysbiosis – see our infographic above), it may reduce the conversion of the inactive T4 to the active T3.   

Nutrients 

The state of your gut and its microbes can also influence the absorption of micronutrients like iodine, iron and copper, which you need for thyroid health. Your microbes have the ability to increase the bioavailability of iron in the gut by producing short chain fatty acids. Your gut microbes also regulate how much iodine you use and how it is broken down and circulated in the body. Iodine is essential for thyroid health. Inflammatory bowel disease can also impair iodine absorption.

Stress 

When we are stressed, we produce more cortisol (aka your stress hormone), which may also reduce the amount T3 (the active thyroid hormone). Stress comes in all shapes and sizes, perceived or actual, but one source is your gut. Inflammation in your gut, whether through dysbiosis, immune response or gastrointestinal disease, will increase circulating cortisol, which if prolonged can have a negative effect on your T3. 

Constipation 

Low thyroid function can slow down how often you go. We know that transit time is linked with diversity of gut microbes. Constipation comes with its own issues, in particular, the effect on circulating oestrogen levels, which may affect fertility and menopausal symptoms.  

Gallbladder 

Your gall bladder is a bit of an unsung hero. It stores bile. Bile regulates metabolism through changes in thyroid hormones and helps you digest and absorb fats. Research has shown that in those with hypothyroidism, bile acids levels were reduced. Insufficient bile can impair how well you digest and absorb nutrients and how well your body deals with hormones and toxins that it needs to get rid of. 

Probiotics 

Research indicates that specific probiotics may be beneficial on thyroid hormone and function and the availability of minerals. We aren’t at a point to conclusively say which strains do what so more research is needed. 

Final thoughts

Be wary of claims that fixing your gut will fix your thyroid. It simply isn’t that simple and there are so many other factors that play a part. A lot of the research has been done in animals (rats mostly) and us humans are rather different to them! We need bigger trials on humans to understand the complex relationship between thyroid health and gut.