Impact of thyroid hormones on asthma in older adults

OBJECTIVE: Thyroid hormones affect airway contraction, but the specific effects of thyroid hormones on airways are controversial. METHODS: We divided 78 advanced-age men with asthma into 3 groups: type I respiratory failure (RF1), type II respiratory failure (RF2), and no respiratory failure (NRF). Pulmonary function was measured after asthma stabilization. RESULTS: The free triiodothyronine (FT3) level was significantly higher in the RF1 than RF2 group, but the free thyroxine (FT4), total thyroxine (TT4), and thyroid-stimulating hormone (TSH) levels were not significantly different. In the RF1, RF2, and NRF groups, the correlation coefficients between FT3 and the forced expiratory volume in1 s (FEV(1)) were 0.317, 0.627, and 0.213; those between FT3 and the FEV(1)/forced vital capacity (FVC) ratio were 0.287, 0.412, and 0.156; those between FT4 and FEV(1) were 0.214, 0.231, and 0.167; and those between FT4 and the FEV(1)/FVC ratio were 0.211, 0.215, and 0.218, respectively. In the RF1 and RF2 groups, the correlation coefficients between the sum activity of peripheral deiodinases (SPINA-GD) and the FEV(1)/FVC ratio were 0.164 and 0.421, and those between SPINA-GD and FEV(1) were 0.284 and 0.491, respectively. CONCLUSION: The correlation between FT3 and pulmonary function is likely caused by changes in thyroid enzymology.