Association Between the Severity of Obstructive Sleep Apnea Syndrome and Free Thyroid Hormone Levels

Introduction: To analyze the relationship between obstructive sleep apnea syndrome (OSAS) severity and hypothyroidism. The association between apnea–hypopnea index and thyroid hormone levels has also been evaluated.
Methods: This study was conducted retrospectively on 255 patients who underwent a polysomnography test and were diagnosed with OSAS between January 2018 and March 2019. Patients who had chronic diseases and who were using drugs that affected thyroid hormone levels and sleep patterns were not included in the study. Patients’ age and gender; thyroid-stimulating hormone (TSH), T4, and T3 levels; and T3/T4 ratios were compared with OSAS severity.
Results: There was a significant association between advancing patient age and OSAS severity (p<0.001). There was a negative association between OSAS severity and free T4 (p=0.007), free T3 levels (p=0.001), and T3/T4 ratio (p=0.011). Of the 255 patients enrolled in this study, 47 (18.4%) had mild OSAS, 71 (27.8%) had moderate OSAS, and 137 (53.8%) had severe OSAS. OSAS was more common in males. The prevalence of hypothyroidism was two times more common in females. Hypothyroidism frequency was 6% in the study group. Nevertheless, there was no significant association between OSAS severity and gender and TSH levels.
Discussion and Conclusion: Lower free T3 and free T4 levels will escalate OSAS severity. It is recommended to evaluate thyroid hormone status especially in elder patients with OSAS.

Keywords: Obstructive sleep apnea syndrome, thyroid hormones, thyroxine, triiodothyronine