A large population-based case control and cohort study conducted last year finds that patients with hypothyroidism or hyperthyroidism are not at increased risk for contracting SARS-CoV-2.
Patients with hypothyroidism or hyperthyroidism were thought to possibly have an increased risk of developing a severe course of COVID-19 because SARS-CoV-2 uses angiotensin converting enzyme 2 (ACE2) as as an entry point for a host cell infection. And, serum ACE levels are associated with thyroid function. Plus, thyroid patients have a higher incidence of cardiovascular conditions. But in this study, which was conducted by Thomas H. Brix, MD, PhD, and colleagues from Odense University Hospital in Denmark, and published online in February as a correspondence in The Lancet, shows that thyroid patients have no increased risk of contracting SARS-CoV-2 and COVID-19.
Brix et al. conducted a population-based case control and cohort study in Denmark to evaluate the risk of contracting SARS-CoV-2 and document the possible prognosis of an infection in patients with hypothyroidism or hyperthyroidism. The study included 2,400,609 million women and men in Demark who tested negative for SARS-CoV-2 and 28,078 women and men who tested positive for the condition between February 27 and Sept. 30, 2020.
Patients using levothyroxine were defined as having hypothyroidism, patients using anti-thyroid drugs were defined as having hyperthyroidism. Patients who not treated for any thyroid condition were defined as having euthyroid, or a normally functioning thyroid gland.
The cohort study included 16,502 patients who tested positive for SARS-CoV-2 between February 27 and Aug 31, 2020 and of these, 572 (3.5%) had hypothyroidism and 75 patients had hyperthyroidism. The crude analysis showed that the use of levothyroxine was associated with an increased risk of death (RR 2.39 [95% CI 1∙80–3∙19]), hospitalization (2.15 [1.84–2.50]), intensive care unit admission (1.88 [1.23–2.87]), mechanical ventilation (1.75 [1.06–2.87]), and dialysis (3.24 [1.63–6.44]).
The case-control study included 809 SARS-CoV-2-positive patients with hypothyroidism, and 7,994 (of 280,007) SARS-CoV-2-negative patients with hypothyroidism. And, it included 91 SARS-CoV-2-positive patients with hyperthyroidism and 936 hyperthyroidism patients who were negative for SARS-CoV-2.
After accounting for covariates the associations waned, but not for hospitalization (1.19 [1.02–1.40]) and dialysis (2.23 (1.06–4.69]), which remained above the null value however, this may have been due to the presence of other comorbidities and treatments for those comorbid conditions, the authors wrote.
In a review of population-based data, the risk of contracting SARS-CoV-2 did not differ between patients with hypothyroidism or hyperthyroidism as compared to the control group. Nor did the risk of developing adverse outcomes disproportionately affect patients with either condition.
A review of data from a patient cohort of 3,703 patients from New York City showed similar findings for patients with hypothyroidism.
“These results suggest that receiving treatment for thyroid dysfunction should not affect the clinical management of the patient’s risk of acquiring SARS-CoV-2 infection, or the management of patients who already contracted the infection. The crude analysis shows an excess risk of adverse outcomes of SARS-CoV-2 infection in patients treated for hypothyroidism and hyperthyroidism, but these associations attenuate after adjustment for comorbidity and temporal changes in the Danish SARSCoV-2 test strategy,” Brix et al. write.
The authors theorize that a hypothyroidism or hyperthyroidism diagnosis did not influence the risk or course of a SARS-CoV-2 infection possibly due to the effect of thyroid hormones on immune response during infection. Or, perhaps the distribution and activity of angiotensin converting enzyme 2 (ACE2) was not sufficient enough to influence the risk and course of SARS-CoV-2.
“Possibly most important, all the patients in our study received treatment with levothyroxine or anti-thyroid drugs. Thus, we cannot rule out that our patients were euthyroid or that the severity of thyroid dysfunction at the time of the SARS-CoV-2 infection was minor and therefore without influence on the immune response during the infection,” the authors wrote. “Our results suggest that patients treated for hypothyroidism or hyperthyroidism do not have an increased risk of contracting SARSCoV-2 infection. The results also suggest that treatment for thyroid dysfunction, when controlling for relevant confounding, does not influence the prognosis of SARS-CoV-2 infection.”
Thomas H Brix, Laszlo Hegedüs, Jesper Hallas, Lars C Lund. “Risk and course of SARS-CoV-2 infection in patients treated for hypothyroidism and hyperthyroidism,” The Lancet. Published online February 19, 2021 and Vol 9 April 2021. https://doi.org/10.1016/ S2213-8587(21)00028-0