1040 Sleep Traits and Obstructive Sleep Apnea in Hypothyroidism: Findings from the EPISONO Database

Abstract Introduction Thyroid regulation is essential for body homeostasis and is closely linked to sleep-wake cycle. Sleep and the hypothalamic–pituitary–thyroid axis interact bidirectionally, influencing the release of thyroid hormones. Thyroid dysfunction may share overlapping mechanisms with sleep disorders, particularly obstructive sleep apnea (OSA), as well as disrupt sleep architecture. This study aimed to investigate the association between thyroid function and sleep, particularly OSA; and to examine the impact of thyroid hormone replacement therapy on sleep characteristics in individuals with hypothyroidism. Methods This cross-sectional study included 761 participants of 769 individuals enrolled in the 4th São Paulo Epidemiologic Sleep Study (EPISONO). Thyroid function was assessed using measurements of thyroid-stimulating hormone (TSH), free thyroxine (FT4), and information on thyroid hormone replacement therapy. Sleep parameters and OSA diagnosis were obtained through full-night polysomnography. Results Hypothyroidism was identified in 12.6% of the sample. Individuals with hypothyroidism presented lower sleep efficiency, longer wakefulness after sleep onset (WASO), higher oxygen desaturation, and a higher apnea-hypopnea index. The OSA frequency in the hypothyroidism subgroup was 49.5%, with severe OSA being more prevalent (25.4%) than non-severe OSA (11.4%). TSH levels were associated with increased odds for severe OSA, even after adjustment. In parallel, severe OSA was related to more than twice the odds of hypothyroidism, suggesting a reciprocal relationship between the conditions. Among participants with hypothyroidism, those under thyroid hormone replacement therapy slept approximately 49 minutes longer and spent 22 minutes more in N3 sleep compared with those untreated. Conclusion The OSA prevalence among individuals with hypothyroidism was consistent with previously reported findings. Higher TSH levels were related to augmented OSA severity, and severe OSA increased the risk of hypothyroidism. Thyroid hormone replacement therapy improved sleep architecture, particularly by increasing restorative N3 sleep and total sleep duration in subjects with hypothyroidism. These findings underscore the importance of incorporating early thyroid function screening into the care of individuals with OSA and, conversely, evaluating patients with thyroid dysfunction for OSA. Support (if any) Associação Fundo de Incentivo à Pesquisa (AFIP), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (2020/13467-8 and 2021/13004-0).