• Dr Izzy Smith

Gluten and Hashimoto's Disease... What's the deal?

Back in late 2019 at an endocrinology conference I asked the head of the American Thyroid Association about a small study regarding gluten and Hashimoto’s (HD) and if she thought it was worth recommending cutting out gluten in HD? She said, "No, but more research would be beneficial."

I have been meaning to do a post on it since, and after doing some exploring online, I can see why so many people are confused about this topic!

I found many functional health coaches/wellness pages claiming gluten worsens thyroid disease (with citations and sciency explanations), but they were also making claims like adrenal fatigue is real and IgG tests are accurate to diagnose food intolerances (both of which I know are utter BS). Knowing who and what to trust with so many conflicting messages must be so confusing!

If we look at the main study they used to justify that thyroid function is benefited from eliminating gluten, we can see it puts forward an unsubstantiated hypothesis with no solid evidence. The study was small (16 people) and examined patients with both celiac disease and raised thyroid antibodies, but NORMAL thyroid function.

The blog has probably taken me awhile because I knew the evidence was poor but I didn’t want to be biased from my own ideologies e.g. the demonisation of gluten irritates me, but not explain the parts of the study that support a potential hypothesis of gluten impacting Hashimotos.

Furthermore, it touches on complicated/not fully understood topics such as, should people with normal thyroid function have thyroid antibodies tested? And if levels of antibodies alone, are clinically significant/cause symptoms? E.g. If you have Hashimotos on thyroxine, do your thyroid antibodies impact correlate with symptoms.

Before we examine the studies, let's take a refresher on Hashimoto’s (HD); HD is a slow grumbly auto-immune destruction of the thyroid associated with antibodies against two proteins inside the thyroid (Anti- TPO and TG). The course of the disease is usually high antibodies, followed by subclinical hypothyroidism (raised TSH but normal thyroid function) and then low thyroid function requiring hormone replacement in the form of thyroxine. Once someone is on thyroxine, they usually need it lifelong.

However around 20% of the population have these antibodies but only 1-5% have altered thyroid function. Having HD is associated with increased risk of celiac disease, diabetes and other auto-immune conditions.

After a pub-med search I can find two actual studies with control groups looking at gluten and thyroid disease.

A Polish study looked at people with positive TG and TPO antibodies and NORMAL thyroid function. 16 people were put on a gluten free diet, and 18 remained on a normal diet. The gluten free diet had a decrease in their antibody levels by about 20% but thyroid function remained normal and unchanged in both groups.

Apart from that the clinical significance of antibodies alone is unclear… The MAJOR caveat to this study was that these people were also all positive for the highly specific Celiac Disease antibody, anti-TTG. Unlike the antibodies in HD where 20% of the population are positive but only a few % have HD, the presence of celiac antibodies means you highly likely have celiac disease.

Consequently, it’s likely, most, if not all of these people had early or undiagnosed celiac disease. By treating the inflammatory process from the celiac disease, this could potentially impact thyroid health through a variety of mechanisms (e.g. celiac disease is associated with selenium deficiency which is known to exacerbate HD) and regardless of thyroid function, everyone with celiac disease needs to avoid gluten.

Furthermore, these people all had normal thyroid function the entire time and the majority of people with raised thyroid antibodies don’t go on to get low thyroid function anyway.

These studies demonstrate how people must not properly read or understand research, or alternatively choose to manipulate the findings of a study in order to support an unproven idea.

To actually understand if gluten was relevant in thyroid disease you’d need to;

1. Do a study with bigger numbers (16 people is tinsy)

2. Do a study on people without celiac disease (apart from confounding results, anyone with celiac disease needs a gluten free diet anyway so what’s the point?)

3. Follow people for longer and see if a gluten free-diet decreased the progression of people with raised thyroid antibodies with normal or sub-clinical thyroid function, developing low thyroid function?

4. Do a study on people with low thyroid function/ advanced HD to see if gluten impacted thyroid function/thyroxin requirements? And if it impacted antibodies, did this have a clinical impact? The latter is important as most people with HD on thyroxine, need it lifelong as essentially the thyroid has already been too damaged. However, the clinical significance of antibodies in people with established HD and symptoms such as fatigue needs further investigation.

The other study was an Italian study that also looked at people with newly diagnosed celiac disease and found some people’s thyroid function improved once their celiac disease was also treated through the elimination of gluten. Similar to the polish study, it can’t really be applied as findings in people without celiac disease.

Long story short… If you have HD should you cut out gluten?

Essentially there isn’t any evidence that gluten impacts thyroid function, unless you already have celiac disease and, in that case, it needs to be eliminated anyway. The studies on thyroid/celiac/gluten create a hypothesis that gluten could potentially impact thyroid antibodies, but no real evidence that it happens outside of celiac disease, or that it impacts actual thyroid function.

If you have HD, it is definitely important to be screened for celiac as they commonly occur together. However, if you don’t have celiac, from the available evidence I would not currently recommend cutting out gluten as these foods are usually higher in fibre, protein and certain micronutrients than their GF versions.

However, if you’ve heard positive anecdotes about gluten and thyroid function and want to try a gluten-free diet despite the lack of evidence, there’s no harm done (provided you’ve still got a healthy diet with lots of fibre) and these studies do provide a potential hypothesis that it could benefit antibody levels (but with all the caveats I listed above).

If you are doing this, I would consider having your thyroid antibodies and function tested before and after. Obviously from individual results it’s impossible to gain actual evidence of cause and effect, but it may benefit you having something objective to help you decide what lifestyle measures impact your thyroid function. If there’s no change, it seems silly to cut out so many foods for no reason.

Finally, remember there is evidence that severe Vitamin D and selenium deficiency or excessive iodine supplementation (taking actual supplements not the amounts found in salt or food) can increase the risk of HD and thyroid problems so make sure you’ve got those basics covered before trialing treatments with no or minimal evidence😊

Prevalence of thyroid disorders in untreated adult celiac disease patients and effect of gluten withdrawal: an Italian multicenter study - PubMed (nih.gov)

The Effect of Gluten-Free Diet on Thyroid Autoimmunity in Drug-Naïve Women with Hashimoto's Thyroiditis: A Pilot Study - PubMed (nih.gov)

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