Thyroid and Type 1 Diabetes: What’s to Know?

Type 1 diabetes (T1D) is an illness in which the immune system produces antibodies that attack the body’s own cells (insulin-producing pancreatic cells).

Just like T1D, many autoimmune conditions are due to a genetic predisposition to producing antibodies that attack the body’s own organs. It’s not uncommon to see other autoimmune diseases in people with T1D, such as celiac disease (gluten intolerance) or thyroid conditions. 

Thyroid disease and blood sugar

The thyroid is a butterfly-shaped gland located in the throat. It plays a major role in regulating many bodily functions, including metabolism (transforming food into energy).

When the thyroid isn’t working properly, many aspects of physical, mental and emotional well-being can be impacted. Thyroid conditions also disrupt normal metabolism, which can make blood sugar management even more complicated.

There are two more frequently observed forms of autoimmune thyroid disease among people with T1D:

  • Hashimoto’s thyroiditis – most prevalent.
  • Graves’ disease (or Basedow’s disease) – rarer.

These conditions affect more women than men.

Hashimoto’s thyroiditis

In people with Hashimoto’s thyroiditis, the immune system attacks and eventually destroys the thyroid (similar to insulin-producing cells that get destroyed in T1D). This means the thyroid can no longer produce enough hormones, leading to hypothyroidism, which can manifest through different symptoms:

  • Fatigue
  • Sensitivity to cold
  • Goitre, or enlarged thyroid gland, which can cause a sensation of fullness in the throat
  • Weight gain
  • Constipation
  • Feeling of mental fog
  • Slowed heart rate
  • Hair loss
  • Irregular or heavier periods and infertility
  • Less cheerful mood or depression
  • Muscle aches

Many other life events and illnesses can cause these symptoms. 

This disease slows down metabolism and can lower blood sugar levels. As a result, hypothyroidism can sometimes trigger a glycemic imbalance (more hypoglycemic episodes) of unknown origin.

Graves’ or Basedow’s disease

In Graves’ disease, the body attacks the thyroid, leading it to produce too many hormones. This is known as hyperthyroidism, which can manifest through different symptoms:

  • Weight loss
  • Increased heartbeat
  • Irritability
  • Fatigue and/or weakness
  • Goitre, or enlarged thyroid gland, which can cause a sensation of fullness in the throat
  • Heat sensitivity
  • Nervousness
  • Diarrhea
  • Tremors
  • Insomnia
  • Bulging eyes (known in medical terms as “Graves’ ophthalmopathy”) 

This disease increases metabolism and can raise blood sugar levels. As a result, hyperthyroidism can sometimes trigger a glycemic imbalance (more hyperglycemic incidents) of unknown origin.

Diagnostic and treatment

Hypothyroidism and hyperthyroidism can both affect the blood sugar levels of people with diabetes, but their impact is highly variable from one person to another. 

The thyroid-stimulating hormone (TSH) is a hormone that reflects how the thyroid is functioning. It can easily be measured through a blood test that is generally done once a year. In some cases, the doctor can also ask for the thyroid antibody (anti-TPO/TSI) count, which reflects the autoimmune process and can sometimes be useful for diagnostics. The antibody count can also be useful for identifying people who are at risk of developing hypothyroidism or hyperthyroidism.

Although there are no preventive treatments, these diseases can be managed very effectively.

  • For hypothyroidism, a drug called Synthroid (Levothyroxine) is taken in the form of a once-daily pill, in order to replace what the thyroid is no longer able to produce, and to reduce or even eliminate symptoms. Blood tests are done to check whether the treatment needs adjustment. It’s better to avoid taking dairy products or calcium and iron supplements at the same time as this treatment, because they can reduce absorption.
  • For hyperthyroidism, which is rarer, symptoms are treated by blocking the production of thyroid hormones using antithyroid drugs, by destroying hyperactive thyroid cells using radioiodine, or by surgically removing the thyroid (thyroidectomy).

Autoimmune diseases often develop silently. This means that increased vigilance and regular testing are required to make sure they are treated as early as possible and to avoid symptoms and complications. However, there is no consensus about which diseases should be targeted through systematic testing or about the frequency of those tests among people with T1D.

Through the BETTER registry, we identify the most frequent autoimmune conditions. Among the 15% of adults with T1D who have reported having at least one other autoimmune disease, 25% had a thyroid condition. 


  • Fleiner, Hanne F et al.“Prevalence of Thyroid Dysfunction in Autoimmune and Type 2 Diabetes: The Population-Based HUNT Study in Norway.” The Journal of clinical endocrinology and metabolism vol. 101,2 (2016): 669-77. doi:10.1210/jc.2015-3235
  • Riley, W J et al. “Thyroid autoimmunity in insulin-dependent diabetes mellitus: the case for routine screening.” The Journal of pediatrics vol. 99,3 (1981): 350-4. doi:10.1016/s0022-3476(81)80316-2
  • Umpierrez, Guillermo E et al. “Thyroid dysfunction in patients with type 1 diabetes: a longitudinal study.” Diabetes care vol. 26,4 (2003): 1181-5. doi:10.2337/diacare.26.4.1181
  • Mitrou, Panayota et al. “Insulin action in hyperthyroidism: a focus on muscle and adipose tissue.” Endocrine reviews vol. 31,5 (2010): 663-79. doi:10.1210/er.2009-0046