To determine the influence of COPD on thyroid hormone levels.

We performed a meta-analysis after conducting a literature search in PubMed, Embase, Web of Science, the Cochrane Library, ScienceDirect, and the Virtual Health Library from database inception to December 31st, 2023. We employed the inverse variance method with a random effects model to calculate the effect estimate as the mean difference (MD) and 95 % confidence interval (CI). We calculated the heterogeneity with the I² statistic and performed a meta-regression analysis based on age, sex, and smoking status. The PROSPERO registry number was CRD42024492108.

The meta-analysis included 25 studies with 1613 patients with COPD and 1792 controls. The pooled MD (95 %CI) for TSH and total T3 were −0.26 mUI/L (−0.46, −0.07); p = 0.009, and −0.15 pg/mL (−0.29, −0.00); p = 0.04 respectively. There was no difference for free T3 and T4 and for total T4 between patients and controls. Heterogeneity was high in all cases. The patients with acute exacerbation of COPD had lower levels of TSH, free and total T3, pooled MD for TSH -0.58 mIU/L (−0.86, −0.31); p < 0.001, for free T3 -0.80 pg/mL (-1.53, -0.31); p < 0.001 and for total T3 -0.21 ng/mL (-0.33, -0.08); p < 0.001. TSH and total T3 levels were lower in patients with more severe airflow obstruction. The meta-regression analysis showed that the percentage of males and smokers in each study could explain the heterogeneity in T4 values.

TSH and T3 levels are decreased in patients with COPD, particularly in severe stages and during acute exacerbations.