Hashimoto’s disease is an autoimmune disorder where the immune system attacks the thyroid gland, causing chronic inflammation and hypothyroidism (low thyroid hormone production). Diabetes is characterized by high blood sugar resulting from the body’s inability to produce or effectively use insulin. While Hashimoto’s disease does not directly cause Type 2 Diabetes, a strong relationship exists, particularly with Type 1 Diabetes, which is also an autoimmune disease. Understanding these connections is important for managing both conditions and recognizing the increased risk of developing one if the other is present.
Shared Autoimmune Pathways
The immune system’s attack in Hashimoto’s disease increases the risk of developing other autoimmune conditions, most notably Type 1 Diabetes (T1D). Both are classified as organ-specific autoimmune diseases, meaning the immune system targets and destroys cells in a specific organ—the thyroid in Hashimoto’s and the insulin-producing beta cells in the pancreas for T1D. This frequent co-occurrence is sometimes categorized as a variant of Autoimmune Polyglandular Syndrome Type 3 (APS3).
This shared vulnerability stems from common genetic factors, such as specific variations in Human Leukocyte Antigen (HLA) genes. These HLA genes are involved in presenting foreign invaders to the immune system, and certain types are strongly linked to the development of both T1D and Hashimoto’s. The presence of one autoimmune condition indicates a systemic predisposition for the immune system to launch attacks on other endocrine glands.
The prevalence of Autoimmune Thyroid Disease (AITD), with Hashimoto’s being the most frequent, occurs in a significant number of Type 1 Diabetes patients, ranging from 17% to 30% of all diagnosed cases. The body’s immune response, once activated and producing autoantibodies against the thyroid, is more likely to develop autoantibodies that target the pancreatic beta cells, leading to T1D. For example, the presence of anti-thyroid peroxidase (anti-TPO) antibodies, a marker for Hashimoto’s, has been found to precede the onset of changes indicating insulin resistance in some individuals. This clear immunological overlap means the two conditions frequently coexist, rather than one directly causing the other through a metabolic pathway.
Hypothyroidism’s Impact on Glucose Control
The relationship between Hashimoto’s and Type 2 Diabetes (T2D) is different, driven primarily by the metabolic consequences of hypothyroidism. Thyroid hormones regulate overall metabolism, and low levels slow down many bodily functions, including those that manage blood sugar. This metabolic slowdown is directly connected to the mechanism of T2D development, which centers on insulin resistance.
Hypothyroidism can significantly worsen insulin resistance, a condition where the body’s cells become less responsive to the effects of insulin. When cells resist insulin, the pancreas must produce more insulin to manage blood sugar, which can eventually lead to pancreatic burnout and T2D. Studies have demonstrated that even subclinical hypothyroidism is associated with increased insulin resistance in people with normal blood glucose levels.
The slowed metabolism associated with low thyroid hormones promotes weight gain and increased fat storage, particularly in the abdominal area, which is a known risk factor for developing insulin resistance. Low thyroid hormone levels also slow the body’s clearance of insulin from the bloodstream, leading to persistently higher insulin levels. This contributes to metabolic dysfunction, increasing the risk of developing Type 2 Diabetes. Stabilizing thyroid hormone levels through treatment can improve insulin sensitivity and aid in the management of T2D.
Clinical Screening and Monitoring
Given the strong connections, clinical protocols emphasize routine screening for the co-occurrence of Hashimoto’s and diabetes. Patients diagnosed with Hashimoto’s should be routinely monitored for both Type 1 and Type 2 Diabetes, as the risk for both is elevated. Monitoring typically includes periodic blood tests such as Hemoglobin A1C (HbA1C) and fasting glucose tests to detect T2D or prediabetes.
For those with Hashimoto’s, screening for Type 1 Diabetes risk involves testing for specific autoantibodies that target the pancreas. Conversely, individuals diagnosed with Type 1 Diabetes should be regularly screened for thyroid dysfunction using a Thyroid-Stimulating Hormone (TSH) test and anti-TPO antibody testing. Professional bodies recommend that women with T1D, in particular, be screened for thyroid disease due to their increased risk.
Treating the underlying hypothyroidism is a foundational part of the overall management plan, as thyroid hormone replacement therapy (levothyroxine) can improve glucose metabolism. For patients managing Type 1 Diabetes, recurrent episodes of low blood sugar may indicate developing hypothyroidism, since low thyroid function affects how the body responds to insulin. Regular monitoring allows healthcare providers to adjust treatment to prevent complications and ensure better health outcomes.