People often find the second condition after the first. Someone with celiac disease, a few years past diagnosis, complains of a tiredness the diet does not explain. Or someone who has been on levothyroxine for years learns they are celiac after an episode of anemia. The two conditions turn up together far more often than chance would allow, and knowing that changes two things: screening, and the dose of thyroid medication.

Two conditions, one shared terrain

Celiac disease is an autoimmune condition: triggered by gluten, the immune system attacks the lining of the gut. Hashimoto’s thyroiditis is another one: the immune system attacks the thyroid, which ends up producing too little hormone (an underactive thyroid). Graves’ disease, rarer, is its mirror image: the thyroid races (an overactive thyroid).

These conditions share a genetic background, the HLA-DQ2 and DQ8 genes we cover here, along with other immune-regulation genes, and the same kind of misfire. Having one raises the risk of the other. The studies agree: autoimmune thyroid conditions are three to four times more common in people with celiac disease, and affect about one in ten over a lifetime. In the other direction, celiac disease is several times more common in people with Hashimoto’s than in the general population.

One more factor is under discussion: untreated gut inflammation may encourage other autoimmune conditions to appear. It is one of the arguments for a strict gluten-free diet, even with no digestive symptoms.

The signs that should make you think of the thyroid

They are misleading, because they look like the signs of a diet that is not being followed properly, or of a deficiency:

  • Underactive thyroid (Hashimoto’s): persistent tiredness, weight gain with no change in eating, feeling cold, dry skin, hair falling out, constipation, everything slowing down, low mood, irregular periods.
  • Overactive thyroid (Graves’): jitteriness, palpitations, weight loss despite a good appetite, tremor, sweating, diarrhea, insomnia.

Someone with celiac disease who is well followed up and still tired, with normal antibodies and a clean deficiency panel, has good reason to have their TSH tested. Anemia and the thyroid are the first two things to look at when tiredness has no explanation.

What it means for screening

The guidance is straightforward:

  • When celiac disease is diagnosed, a TSH test (the hormone that drives the thyroid) is part of the initial work-up in most protocols, alongside the deficiency panel.
  • After that, a regular check, every one to two years depending on the team, or as soon as a sign appears. Thyroiditis can show up years later.
  • In the other direction, someone with autoimmune thyroiditis who has digestive symptoms, anemia, osteoporosis or unexplained tiredness may be screened for celiac disease with a blood test, while still eating gluten, as always for that test.

Screening in the thyroid to celiac direction is not routine everywhere; it is a conversation to have with your doctor, based on your symptoms.

The gluten-free diet and your levothyroxine dose

This is the most important practical point, and the least well known. Levothyroxine, the treatment for an underactive thyroid, is absorbed in the small intestine. A gut damaged by celiac disease absorbs it poorly: some people need unusually high doses, or have a TSH that refuses to settle, before their celiac disease is found.

Once the gluten-free diet starts and the lining heals (the timelines are here), absorption improves, and a dose that used to be right becomes too strong. That is why TSH should be checked in the months after the diet begins, and the dose adjusted if needed. Doctors usually know this, but it does no harm to remind them.

Two pharmacy details: levothyroxine is taken on an empty stomach, well apart from iron and calcium, which get in the way of absorption, and people with celiac disease often take both. And the tablets sometimes contain lactose, rarely wheat starch; the patient leaflet will say.

If you take levothyroxine, starting the gluten-free diet can make a dose that used to be right too strong: a healing gut absorbs it better. Have your TSH checked in the months that follow, and never change the dose yourself.

Does a gluten-free diet “fix” the thyroid?

It is a common question, and the honest answer has shades to it. In someone with celiac disease, a strict diet is essential, and some studies suggest it slows the progression of associated thyroiditis; the data are not conclusive. In someone with Hashimoto’s but no celiac disease, there is nothing to show that a gluten-free diet improves the thyroid; it is not recommended without a diagnosis, for the reasons we set out elsewhere.

In short

  • Autoimmune thyroid conditions are three to four times more common in people with celiac disease: around one in ten.
  • Shared genetic and immune background; untreated inflammation may play a part.
  • TSH at diagnosis, then regularly; celiac screening for people with Hashimoto’s who have symptoms.
  • The diet improves levothyroxine absorption, so the dose may need to come down. Check TSH after starting the diet.
  • Unexplained tiredness in someone with well-managed celiac disease: look at iron, then the thyroid.

Sources

  • Elfström P., Montgomery S. M., Kämpe O., Ekbom A., Ludvigsson J. F. Risk of thyroid disease in individuals with celiac disease. Journal of Clinical Endocrinology & Metabolism, 2008; 93(10): 3915-3921. Swedish cohort of 14,000 patients with celiac disease: risk of autoimmune thyroiditis three to four times higher.
  • Sategna-Guidetti C. et al. Prevalence of thyroid disorders in untreated adult celiac disease patients and effect of gluten withdrawal. American Journal of Gastroenterology, 2001; 96(3): 751-757.
  • Al-Toma A. et al. European Society for the Study of Coeliac Disease (ESsCD) guideline for coeliac disease and other gluten-related disorders. United European Gastroenterology Journal, 2019; 7(5): 583-613. Follow-up recommendations, including TSH testing at diagnosis.
  • NICE (United Kingdom), Coeliac disease: recognition, assessment and management, guideline NG20, 2015: offer celiac disease testing to people with autoimmune thyroid disease.
  • Assurance maladie, Intolérance au gluten (maladie cœliaque), ameli.fr, patient information (France).

This information does not replace medical advice. Thyroid monitoring and levothyroxine adjustments are done with your doctor or endocrinologist: never change a dose on your own.