The Coronavirus May Mess With Thyroid Levels, Too

Early studies suggest that the thyroid is yet another organ affected by the pandemic coronavirus

As the devastating outbreak of Covid-19 spread in Italy in March, doctors became curious if the ruthless virus, which seemed to wreak unpredictable havoc on the body, was mucking with important organs like the thyroid. At the Ca’ Granda Main Polyclinic Hospital in Milan, it was feasible for them to investigate this because they routinely test critical care patients’ levels of thyroid-stimulating hormone, or TSH, which is an indirect indicator of thyroid health. So Ilaria Muller, MD, PhD, an endocrinologist at the hospital, began comparing blood test results from patients admitted to that critical care unit with data from other patients in the previous year to see if there was a difference in their thyroid hormones.

The thyroid, a butterfly-shaped gland that sits below the Adam’s apple at the base of the throat, performs crucial functions in the body. It secretes hormones that maintain a person’s metabolic rate, fertility, and digestive system, just to name a few of its many responsibilities. Damage to this organ can cause a wide range of symptoms, including weight gain and brain fog, and has even been linked to an increased risk of miscarriage and heart disease.

After excluding people with preexisting thyroid conditions from their analysis, Muller and her colleagues ended up with data from 85 critical care patients from March and April of this year, all of whom had Covid-19, and from 78 people admitted to that same unit during those months in 2019. The study, published July 30 in the Lancet Diabetes & Endocrinology journal, found that 13 of those people with Covid-19, around 15%, were experiencing thyrotoxicosis, a condition in which there is an excess of thyroid hormone in the blood. This can happen when the thyroid is damaged, causing an unusually large release of stored up hormone reserves. By comparison, only one of the 78 patients from the 2019 group had evidence of thyrotoxicosis.

The researchers believe that Covid-19, caused by the virus SARS-CoV-2, might be a risk factor for an atypical form of thyroiditis, which is characterized by inflammation of the thyroid that can lead to thyrotoxicosis. Viral thyroiditis, also known as subacute thyroiditis, is a mystery in that doctors aren’t sure exactly which viruses can cause it, but researchers have found circumstantial evidence linking it to everything from influenza to hepatitis. “Lots of viruses can affect the thyroid,” Muller says. “So why not SARS-CoV-2?”

Curiously, the people with Covid-19 in critical care with thyrotoxicosis had high levels of the thyroid hormone thyroxine, but not the elevated triiodothyronine levels typically seen in viral thyroiditis. They also never experienced any neck pain, which is a key feature of viral thyroiditis. (I know this symptom very well personally because I experienced this condition a couple years ago and had a giant, excruciating bulge at the base of my neck when I was finally diagnosed.)

Muller notes that thyroid cells have the ACE-2 receptor on their surface, which SARS-CoV-2 uses to enter cells. She suspects that in severe cases the virus is able to infiltrate the thyroid, but this might not happen commonly in milder cases: Only one of the 41 Covid-19 patients without preexisting thyroid conditions who received low-intensity care at the hospital in March and April had test results indicating thyrotoxicosis.

Mounting evidence

Other groups have uncovered evidence suggesting Covid-19 might disrupt thyroid hormones. A study published in July from another Italian team looked at data from almost 300 people with Covid-19 and found evidence of thyrotoxicosis in around 20% of them, particularly those who seemed to have systemic inflammation from the infection.

Gherardo Mazziotti, MD, PhD, an endocrinologist and associate professor at Humanitas University of Milan who led this work, explains that the long-term effects are still under exploration. “It is reasonable to hypothesize that the thyroiditis induced by SARS-CoV-2 is transient,” Mazziotti says. He adds, though, that “we cannot exclude” that in some cases it might cause lasting, chronic thyroid dysfunction. Viral thyroiditis is generally just a transient condition, but in anywhere from 5% to 20% of cases the thyroid damage means that patients require lifelong thyroid hormone replacement medication. Muller and her team followed up with eight of the people with Covid-19 in their study who had signs of thyrotoxicosis. Ultrasounds of their thyroid glands showed signs of abnormalities, including three patients in which these scans showed spots indicating that some cell death might have occurred.

“These studies indicate that patients with Covid-19, especially those with severe illness, should be monitored for signs and symptoms of thyroid problems and that there should be a low threshold for checking thyroid blood tests.”

Despite the spots on some of the ultrasounds, all the people with Covid-19 in Muller’s study seem to have recovered thyroid function. She says that her team plans to do stress tests in the future to see if their thyroids are still able to work optimally when challenged. It’s too early to say whether there is any link between the abnormal thyroid levels seen in some severely ill Covid-19 patients and reported Covid-19 effects such as a racing heartbeat and hair loss, which can occur with thyroid hormone changes. But Muller says there’s ample evidence for doctors to consider screening people with Covid-19 for thyroid abnormalities to see whether these individuals should be followed up once they recover to ensure the organ is working well. (She also notes that preexisting thyroid conditions do not appear to be a risk factor for Covid-19, according to her preliminary analysis.)

In addition to these studies, there have been at least a trio of case reports from Italy linking the novel coronavirus to thyroiditis. Meanwhile, a July study from researchers in China found thyroid level abnormalities, although these didn’t have the classical signature of thyroiditis. However, the authors noted that these patients did not have their thyroid levels checked when they were admitted to the hospital and were already receiving steroids, which can affect hormone levels.

Some endocrinologists say it’s too early to know if the link is solid. Erkam Sencar, MD, an endocrinologist at Diskapi Yildirim Beyazit Training and Research Hospital in Ankara, Turkey, remains skeptical that Covid-19 carries a heightened risk for thyroiditis. “As an expert examining a large number of thyroid patients, I have not observed an increase in [viral thyroiditis] cases,” he says.

Sencar also cautions that there might be confounding factors in these studies such as patients’ exposure to the iodine injection they receive to improve the image of CT scans used to assess lung health. Iodine can have a big effect on thyroid function. Furthermore, he notes that subacute thyroiditis typically occurs two to six weeks after viral infection. The timing of the thyroid hormone changes the researchers are seeing with Covid-19 are concurrent with the infection, so this makes him skeptical that it is explained by something like subacute thyroiditis.

Muller says that it’s unlikely the Covid-19 patients in her study received iodine before their blood was drawn upon admittance to the hospital and that this contrast agent isn’t always used in the kind of CT scans they receive. She also stresses that she and her colleagues were careful to call this condition “atypical” thyroiditis given it doesn’t seem to fit the pattern of subacute thyroiditis. The Covid-19 patients might have some elements of what’s known as nonthyroidal illness syndrome, a condition in which the body has difficulty converting thyroid hormones.

Other endocrinologists say that it might be useful to watch for thyroid hormone abnormalities in Covid-19 patients. “These studies indicate that patients with Covid-19, especially those with severe illness, should be monitored for signs and symptoms of thyroid problems and that there should be a low threshold for checking thyroid blood tests,” says Victor J. Bernet, MD, chair of the endocrinology department at the Mayo Clinic Florida and president-elect of the American Thyroid Association. Bernet notes that autopsies of patients who died in the outbreak of SARS, a disease closely related to Covid-19, in the early 2000s found signs of thyroid inflammation when evaluating thyroid tissue under a microscope.

James Hennessey, MD, director of clinical endocrinology at the Beth Israel Deaconess Medical Center in Boston, suggests a similar approach and says doctors should be aware about this possible link “so that thyroid function testing be performed in a timely manner” when nonspecific symptoms such as a rapid pulse rate suggest a potential thyroid basis.

Health reporter uncovering overlooked science. Follow her on Twitter at @rkhamsi and get her new articles here:

Sign up for Inside Your Head 🧠

By Elemental

A weekly newsletter exploring why your brain makes you think, feel, and act the way you do, by Elemental senior writer Dana Smith. Take a look.

By signing up, you will create a Medium account if you don’t already have one. Review our Privacy Policy for more information about our privacy practices.

Check your inbox
Medium sent you an email at to complete your subscription.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store