Overview of Thyroid Function

The thyroid is a gland located in front of the trachea and serves important metabolic functions. It works by extracting iodine from blood and converting it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3). T4 is the main product of the thyroid and can be converted to T3, which is more potent. Thyroid hormone production is stimulated by the pituitary gland, and the T3 and T4 hormones circulate throughout the body to regulate metabolism.

Because thyroid function is critical to cellular metabolism, its dysfunction can cause detrimental health effects. There are several thyroid disorders, of which the two major ones are: hypothyroidism and hyperthyroidism. Both conditions are often invoked by an autoimmune process.

Hypothyroidism

Hypothyroidism (very commonly a result of Hashimoto’s thyroiditis) may affect anywhere from 2-20% of the population. This condition is characterized by low levels of thyroid hormones and may have no symptoms at all. The major clinical symptoms include:

Fatigue

Cold intolerance

Weight gain

Sleep dysfunction

Memory problems

Constipation

Hoarse voice

Hearing problems

Tingling, chilling or numb skin sensations

Hair loss

Experts describe that “the diagnosis may be easily performed by the measurement of blood levels of thyroid hormones. Therapy of choice is the administration of thyroxine and the prognosis is very good.” Diagnosis is typically performed based on the levels of thyroid stimulating hormone (TSH) and free T4 levels (see diagram above). Individuals with hypothyroidism often present with low T4 levels, despite elevated TSH levels.

Hyperthyroidism

Hyperthyroidism (very commonly a result of Grave’s disease) is characterized by an overproduction of thyroid hormones. It is relatively rare compared to hypothyroidism, affecting approximately 0.3-1% of the population. The major clinical symptoms of the condition include:

Unexplained weight loss

Increase thirst

Anxiety

Fatigue

Tremors

Sleep disruptions

Shortness of breath

Gastrointestinal discomfort

Sweating

Eye irritation or discomfort

Much like hypothyroidism, hyperthyroidism can be diagnosed by measuring serum levels of TSH, as well as free T4 and T3. In individuals with hyperthyroidism, the TSH levels will often be low (because the pituitary gland is trying to minimize the production of T4 and T3 in response to the high levels of the hormones). Treatment is usually tailored based on the underlying reason for the high thyroid hormone levels, and may include “antithyroid drugs, radioactive iodine therapy, surgery, and in some cases, beta blockers.”

Thyroid Dysfunction in People with Diabetes

People with diabetes are at a higher risk for thyroid disorders than the general population.

Diabetes mellitus (DM) and thyroid disease appear to be closely linked. A recent meta-analysis of all available data in 10,920 patients with DM revealed a mean frequency of thyroid disease of 11%. The data in type 1 DM did not differ from those in type 2 DM, but the prevalence in women was consistently more than twofold than in men.

Why are people with diabetes predisposed to the development of thyroid disease? It likely varies from individual to individual because the disease is most often multifactorial, but researchers suggest that there may be common genetic factors between diabetes and thyroid diseases, as well as other mechanisms related to the intersection of thyroid hormone function with glucose and lipid metabolism. Many of these specific genetic factors and molecular mechanisms are still being unraveled today.

Importantly, thyroid disease can directly affect diabetes management by influencing factors like insulin resistance, hepatic glucose output, insulin production, etc.

Conclusions

The thyroid plays an important role in metabolism throughout the body, and thyroid dysfunction can affect a variety of metabolic processes, including growth, development, insulin production, insulin resistance, and glucose output. Thus, thyroid conditions can directly affect diabetes management.

Often, hypothyroidism and hyperthyroidism stem from autoimmune processes. Both are more prevalent in individuals with diabetes. It is recommended that people with diabetes undergo regular thyroid function screenings for early detection and treatment.

References

De Leo S, Lee SY, Braverman E; “Hyperthyroidism” (2016) Lancet 388(10047): 906-918. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5014602/

Duntas LH, Orgiazzi J, Brabant G; “The interface between thyroid and diabetes mellitus” (2011) Clinical Endocrinology 75(1): 1-9. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2265.2011.04029.x

Kadiyala R, Peter R, Okosieme OE; “Thyroid dysfunction in patients with diabetes: clinical implications and screening strategies” (2010) The International Journal of Clinical Practice 64(8): 1130-1139. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1742-1241.2010.02376.x

Kostoglou-Athanassiou I and Ntalles K’ “Hypothyroidism – new aspects of an old disease” (2010) Hippokratia Quarterly Medical Journal 14(2): 82-87. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2895281/

Triolo TM, Armstrong TK, McFann K, Yu L, Rewers MJ, Klingensmith GJ, Eisenbarth GS, Barker JM; “Additional Autoimmune Disease Found in 33% of Patients at Type 1 Diabetes Onset” (2011) Diabetes Care 34(5): 1211-1213. http://care.diabetesjournals.org/content/34/5/1211.short

Van den Driessche, Eenkhoorn V, Van Gaal L, De Block C; “Type I diabetes and autoimmune polyglandular syndrome: a clinical review” (2009) The Netherlands Journal of Medicine 67(11): 376-387. http://www.njmonline.nl/getpdf.php?id=865

Vanderpump MPJ; “The epidemiology of thyroid disease” (2011) British Medical Bulletin 99: 39-51. https://www.researchgate.net/profile/Mark_Vanderpump/publication/51619844_The_epidemiology_of_thyroid_disease/links/54f35bea0cf24eb8794c2bd6.pdf

Wang C; “The Relationship between Type 2 Diabetes Mellitus and Related Thyroid Diseases” (2013) Journal of Diabetes Research 390534: 1-9. https://www.hindawi.com/journals/jdr/2013/390534/abs/

Read more about autoimmune disease, autoimmune thyroid disease (ATD), diabetes and thyroid, type 1 diabetes, type 2 diabetes.