Diabetes, Hashimoto’s, and an underactive thyroid

Photo: Mae Mu.

Photo: Mae Mu.

The autoimmune connection between an underactive thyroid, excessive weight, and diabetes

Thyroid conditions and diabetes are the two most frequent hormonal problems general practitioners encounter in their daily practice (1).

Today diabetes is grouped in two main forms: type 1 and type 2 diabetes. Both type 1 and 2 diabetes can occur in people diagnosed with Hashimoto’s and an underactive thyroid (1).

Thyroid function and diabetes

Thyroid hormones are necessary for the body to metabolize carbohydrates, as well as for the pancreas to properly function (the organ producing insulin). Low thyroid hormones cause a drop in insulin levels — insulin is a hormone needed to take sugar from the blood to different cells throughout the body.

Low insulin levels cause high blood sugar levels and slows down in cellular function, including muscle contractions and basic brain function. Over longer periods of time low insulin levels can trigger diabetes.

People are at an increased risk of frequent hypoglycemic episodes with an underactive thyroid and low blood sugar symptoms include:

  • Shakiness

  • Weakness

  • Confusion

  • Problems talking

  • A feeling of hunger

  • Loss of consciousness (in extreme cases) (2–4).

Both clinical and subclinical hypothyroidism are connected to insulin resistance, a state where cells in the body stop responding to insulin’s signal to take sugar out of the blood. This results in high blood sugar levels, directly increasing the risk of eye damage and kidney damage (2–4). Insulin resistance can cause the thyroid gland to develop more nodules and become larger in size (5, 6).

Symptoms of insulin resistance include:

  • Fatigue

  • Hunger

  • Brain fog

  • Weight gain (especially around the belly)

  • High blood pressure

People who are diagnosed with diabetes, but are not managing it through lifestyle interventions, are at risk of having lower levels of T3 hormone and high rT3 levels (7,8).

Hashimoto’s and type 1 diabetes

Type 1 diabetes is the most common chronic hormonal condition in children and young people — 4 in 100 children with diabetes type 1 also have Hashimoto’s (9). 1 in 2 relatives of people with type 1 diabetes have an autoimmune thyroid condition (10 -12).

4 in 10 adult patients with type 1 diabetes test positive for TPO antibodies, and are at risk for developing an underactive thyroid (13–15). Type 1 diabetes patients who test positive for glutamic acid decarboxylase antibodies (GADA) have a three and half times higher risk of developing a thyroid condition (16).

3 in 10 adults diagnosed with Hashimoto’s have type 1 diabetes — only half of these patients will have an underactive thyroid, while the other half will have TSH within normal ranges (10, 17).

Type 1 diabetes and Hashimoto’s co-occur often and are inherited, as they share several genes, whose mutation increases the risk of developing either type 1 diabetes, Hashimoto’s, or both (18–25).

Type 1 diabetes patients at an increased risk of developing Hashimoto’s and an underactive thyroid include (17, 26–31):

  • Women

  • Older people

  • Positive for glutamic acid decarboxylase antibodies (GADA)

  • Have had type 1 diabetes for a long time

Hashimoto’s and type 2 diabetes

1 in 10 people with diabetes type 2 will have a thyroid condition too. Women with type 2 diabetes are five times more likely to have Hashimoto’s (32).

The American Thyroid Association guidelines for type 2 diabetes patients advises for frequent thyroid function testing (17).

Risk factors of having both type 2 diabetes and Hashimoto’s include:

  • High TPO antibodies in thyroid patients

  • High estrogen levels and polycystic ovary syndrome (PCOS)

  • Overweight and obesity

Metformin — a medication used to treat patients with type 2 diabetes, obesity, and/or people with PCOS — can normalize TSH levels in diabetic patients with an underactive thyroid (33).

Diabetes is a broad condition with many genetic and environmental triggers, as well as many symptoms and co-occurring conditions. A year ago researchers have further classified diabetes in five instead of two groups, and some of them are more associated with autoimmune conditions (34).

Tracking symptoms, including weight, energy, and focus in the BOOST Thyroid app may help you with your next doctor’s appointment.


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  2. Dimitriadis G, et al. Insulin action in adipose tissue and muscle in hypothyroidism, 2006

  3. Cettour-Rose P, et al. Hypothyroidism in rats decreases peripheral glucose utilisation, a defect partially corrected by central leptin infusion, 2005

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  6. Ayturk S, et al. Metabolic syndrome and its components are associated with increased thyroid volume and nodule prevalence in a mild-to-moderate iodine-deficient area, 2009

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  12. Sougioultzoglou F, et al. Coincidence of high antiislet and antithyroid autoantibody titles in first-degree relatives of patients with type 1 diabetes, 2005

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  14. Kordonouri O, et al. Natural course of autoimmune thyroiditis in type 1 diabetes: association with gender, age, diabetes duration, and puberty, 2005

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  19. Santamaria P, et al. HLA-DQB1-associated susceptibility that distinguishes Hashimoto’s thyroiditis from Graves’ disease in type I diabetic patients, 1994

  20. Kim EY, et al. Polymorphisms of HLA class II predispose children and adolescents with type 1 diabetes mellitus to autoimmune thyroid disease, 2003

  21. Levin L, et al. Analysis of HLA genes in families with autoimmune diabetes and thyroiditis, 2004

  22. Dittmar M, et al. Early onset of polyglandular failure is associated with HLA-DRB1∗03, 2008

  23. Golden B, et al. Genetic analysis of families with autoimmune diabetes and thyroiditis: evidence for common and unique genes, 2005

  24. Ikegami H, et al. The association of CTLA4 polymorphism with type 1 diabetes is concentrated in patients complicated with autoimmune thyroid disease: a multicenter collaborative study in Japan, 2006

  25. Dultz G, et al. The protein tyrosine phosphatase non-receptor type 22 C1858T polymorphism is a joint susceptibility locus for immunthyroiditis and autoimmune diabetes, 2009

  26. Jung ES, et al. Thyroid autoimmunity in children and adolescents with newly diagnosed type 1 diabetes mellitus, 2014

  27. Reghina AD, et al. Thyroid autoimmunity in 72 children with type 1 diabetes mellitus: relationship with pancreatic autoimmunity and child growth, 2012

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  32. Fleiner HF, et al. Prevalence of Thyroid Dysfunction in Autoimmune and Type 2 Diabetes: The Population-Based HUNT Study in Norway, 2016.

  33. Cappelli C, et al. TSH-lowering effect of metformin in type 2 diabetic patients: differences between euthyroid, untreated hypothyroid, and euthyroid on L-T4 therapy patients, 2009

  34. Ahlquist E, et al. Novel subgroups of adult-onset diabetes and their association with outcomes: a data-driven cluster analysis of six variables, 2018