Association of hypothyroidism and respiratory diseases: A cross-sectional study among Europeans using Mendelian randomization.

To explore the causal relationship between hypothyroidism and various respiratory diseases through a 2-sample Mendelian randomization (MR) approach. The genetic summary data of hypothyroidism and pulmonary diseases were obtained from 2 genome-wide association studies. A series of quality control steps were carried out to select instrumental variables. We conducted 2 independent 2-sample MR analyses, including MR-Egger regression, weighted median, random-effects inverse variance weighted method, and weighted model 4 regression models, to evaluate the causal associations between hypothyroidism and asthma, bronchiectasis, bronchitis, pneumonia, and pulmonary embolism. These MR analyses were conducted to assess the causal relationships between them. The inverse variance weighted model showed that hypothyroidism was a risk factor for asthma (odds ratio = 2.605). The intercept term of the MR-Egger regression had a P-value > .05, which indicated the absence of significant genetic pleiotropy. The results of heterogeneity tests with P-values > .05 suggested no heterogeneity among single nucleotide polymorphisms. MR analysis indicated that hypothyroidism elevated the risk of asthma.