Risk of developing pneumonia associated with clinically diagnosed hypothyroidism: a nationwide population-based cohort study.

Hypothyroidism has a detrimental effect on the immune system, which may predispose patients to infection. The risk factors for pneumonia include older age, chronic lung diseases and, most importantly, a decreased immune response against respiratory pathogens. However, evidence of the risk for pneumonia in patients with hypothyroidism is scarce. The high prevalence of hypothyroidism, high annual incidence rate of pneumonia and their interrelationship through the immune system emphasize the importance of understanding the association between the two diseases. This study aimed to determine whether patients diagnosed with hypothyroidism conferred a predisposition to the development of pneumonia. In this 15-year population-based retrospective cohort study, we found that patients clinically diagnosed with hypothyroidism might be at increased risk for the future development of pneumonia. Moreover, in patients with hypothyroidism, the risk of pneumonia may be reduced by thyroxine replacement treatment. Additional prospective cohort studies, which include thyroid function tests and a more accurate clinical diagnosis of pneumonia based on radiological findings, are needed to confirm the effects of hypothyroidism on the risk of developing pneumonia.