The thyroid gland, a small, butterfly-shaped organ located at the base of the neck, acts as the body’s primary metabolism regulator. It produces hormones that influence nearly every organ system, controlling energy use, heart rate, and body temperature. The systemic nature of the COVID-19 pandemic, caused by the SARS-CoV-2 virus, extended its impact far beyond the respiratory tract. Research has shown that the infection can affect multiple endocrine organs, including the thyroid, leading to various forms of dysfunction that emerge during or after the acute illness. Understanding this connection is important for individuals seeking to manage their health during recovery.
How the SARS-CoV-2 Virus Interacts with the Thyroid
The SARS-CoV-2 virus gains entry into human cells by binding its spike protein to the Angiotensin-Converting Enzyme 2 (ACE2) receptor. These receptors are present on various cells throughout the body, including those within the thyroid gland. A consistent finding is the presence of ACE2 receptors on thyroidal pericytes, cells that wrap around small blood vessels.
Infection of pericytes can lead to microcirculatory damage and inflammation, triggering a localized inflammatory response in the gland itself. Another major mechanism involves the body’s overwhelming immune response, often called a “cytokine storm.” High levels of inflammatory molecules, like Interleukin-6 (IL-6), circulate during severe COVID-19 and interfere with the hypothalamic-pituitary-thyroid (HPT) axis. This interference can suppress the release of Thyroid-Stimulating Hormone (TSH), resulting in lower thyroid hormone levels even without direct thyroid damage.
Acute Thyroid Conditions Following COVID-19 Infection
Subacute Thyroiditis (SAT) is one of the most reported conditions linked to SARS-CoV-2, typically developing a few weeks after the initial infection resolves. The characteristic symptom is neck pain, which often radiates to the jaw or ears. This acute inflammation damages the thyroid follicles, causing a massive release of stored hormones into the bloodstream, leading to transient hyperthyroidism. Symptoms include palpitations, anxiety, sweating, and unexplained weight loss, but this phase is generally self-limiting.
Following the hyperthyroid phase, patients often transition into a temporary hypothyroid state, causing fatigue and cold intolerance, though function usually returns to normal within several months. Another common acute finding in severe cases is Non-Thyroidal Illness Syndrome (NTIS), also called euthyroid sick syndrome. NTIS is a temporary, adaptive change where hormone levels appear abnormal on blood tests, but the gland is not diseased. It is a response to severe stress or critical illness, and usually requires no specific treatment, resolving once the underlying COVID-19 illness improves.
Managing Pre-existing Thyroid Disorders During Illness
Individuals with pre-existing thyroid conditions, such as Hashimoto’s thyroiditis or Graves’ disease, need specific consideration during a COVID-19 infection. For patients whose condition is well-controlled, there is no increased risk for contracting the virus or developing a more severe illness. The guidance is to continue all prescribed thyroid replacement or anti-thyroid medications as directed.
Patients taking levothyroxine for hypothyroidism should ensure they have an adequate supply, as maintaining stable TSH levels is important for recovery. For those taking anti-thyroid drugs for hyperthyroidism, a specific concern is the rare side effect of neutropenia, a drop in white blood cell count. Because a low white blood cell count increases vulnerability to infections, patients should communicate with their endocrinologist if they develop a fever or flu-like symptoms while on these medications.
Severe COVID-19 infection, especially when requiring hospitalization, can destabilize existing thyroid control. Medications used to treat severe COVID-19, such as glucocorticoids, can directly affect thyroid hormone metabolism and TSH levels. Close monitoring of thyroid function tests is necessary during and immediately after a severe illness to ensure proper dosage adjustments are made. Existing thyroid therapy should be maintained unless a specialist advises a temporary change.
Persistent Thyroid Problems in Post-COVID Recovery
Even after the acute infection has passed, some individuals experience persistent thyroid dysfunction weeks or months later, contributing to symptoms seen in Post-COVID Syndrome. This is particularly true for patients who had moderate-to-severe illness or developed Subacute Thyroiditis (SAT) during the acute phase. This lingering dysfunction is often characterized by persistent fatigue or sluggishness, which may be misattributed to other aspects of long COVID. For patients who had SAT, the hypothyroid phase can sometimes persist longer than expected, requiring temporary hormone replacement therapy.
Due to the possibility of delayed or persistent thyroid issues, continued monitoring of Thyroid-Stimulating Hormone (TSH) and free T4 levels is recommended for several months post-recovery. Follow-up testing can identify a delayed onset of hypothyroidism or confirm full recovery from an episode of Subacute Thyroiditis, even if initial tests were normal. Identifying and treating these prolonged dysfunctions helps alleviate persistent symptoms like fatigue.