Endocrine Abstracts

JOINT746

Introduction: The hypothalamic–pituitary–thyroid axis controls the circadian clock via the suprachiasmatic nucleus. Chronotype refers to a person’s natural preference for sleep-wake cycles and twenty-four-hour activity patterns. Daytime sleepiness, constant fatigue, and increased daytime sleepiness are common in many diseases, including Hashimoto’s thyroiditis (HT). The evening chronotype may be associated with higher thyrotropin (TSH) levels and a higher risk of hypothyroidism. Concurrently, sleep disorders have become a serious public health problem as they impair endocrine function. The aim of the study was to estimate the association between thyroid status, chronotype, and daytime sleepiness among HT patients.

Material and Methods: The study included 115 patients, 106 women and nine men (43±12 years of age) with clinical, ultrasound, and laboratory-confirmed HT. We used the short Morningness-Eveningness Questionnaire (rMEQ) to assess chronotype and the Epworth Sleepiness Scale (ESS) to evaluate daytime sleepiness. Based on chronotype, patients were categorized into intermediate + morning chronotype (rMEQ>11) and evening chronotype (rMEQ≤11) groups. Patients were, based on the ESS, further categorized into those with normal daytime sleepiness (ESS≤10) and those with increased daytime sleepiness (ESS≥11).

Results: Most patients had normal daytime sleepiness (71.3%), and most of them had an intermediate chronotype (60.9%), while only one patient had a morning chronotype (0.9%). Age was significantly associated with chronotype (χ2=499.278; P = 0.012), with younger patients tending to have an evening chronotype. A significant association was observed between chronotype and thyroglobulin antibodies (TgAb) (χ2=898.614; P = 0.008) and TSH levels (χ2=833.323; P = 0.033). Daytime sleepiness was also significantly associated with TgAb (χ2=1667.721; P = 0.050), TSH (χ2=1531.095; P = 0.050) and fT3 (χ2=618.605; P = 0.024). Free triiodothyronine (fT3) levels were significantly higher in patients with intermediate + morning chronotype than in the evening ones (Z=-2.160; P = 0.031), while no significant differences in thyroid parameters were found between normal and increased daytime sleepiness.

Conclusion: Only 38.3% of patients had an evening chronotype, and only 28.7% had increased daytime sleepiness. The evening chronotype is associated with a higher rate of HT. Sleep affects the secretion of thyroid hormones and leads to a decrease in the amplitude of the circadian rhythm for TSH. The underlying mechanisms are not fully understood and require further investigation. Grant No. IP-FDMZ-2024.2025-09.