Relationship between sleep apnea and thyroid function

Abstract

Sleep apnea is sometimes associated with hypothyroidism, but the significance of thyroid function screening in sleep apnea patients has been controversial. In the present study, we investigated the relationship between thyroid function and sleep apnea in subjects who were suspected to have sleep apnea. We enrolled 156 consecutive subjects suspected of having sleep apnea. Subjects included 117 men and 39 women aged 21 to 84years. They underwent nocturnal multichannel polysomnography during a one-night hospitalization. The examined indices of sleep apnea were apnea-hypopnea index (AHI), lowest oxygen saturation, oxygen desaturation index, longest apnea duration, mean apnea duration, and the percent of apnea time to sleep time. Serum thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were concomitantly measured by electrochemiluminescence immunoassays. Three subjects (1.9%) were diagnosed with primary hypothyroidism (high TSH and low FT4), and one subject (0.6%) with subclinical hypothyroidism (high TSH and normal FT4). No significant difference in the level of TSH, FT3, or FT4 was seen among subjects with different severity of sleep apnea. The mean apnea duration significantly correlated with TSH in both simple and multiple regression analyses. Subjects with lower FT3 (≤3.75pg/ml) showed longer mean apnea time compared to those with higher FT3 (>3.75pg/ml) (24.9 ± 0.8 vs. 20.2 ± 1.2s; P = 0.009). The other indices of sleep apnea did not show significant correlation with thyroid function. These results suggest that the mean apnea duration and TSH/FT3 may be helpful in understanding reciprocity between the two disease states, and for evaluating the validity of thyroid function tests in patients with sleep apnea.