Thyroid Function and Sleep Quality: A Cross-Sectional Analysis of Subclinical Hypothyroidism and Insomnia Symptoms in Adults

Abstract

Background:
Thyroid hormones influence a wide range of physiological processes, including metabolism, mood, and neurological function. Subclinical hypothyroidism (SCH), characterized by elevated thyroid-stimulating hormone (TSH) and normal free thyroxine (fT4), has been inconsistently linked to sleep disturbances. This study investigates the association between SCH and sleep quality in adults.

Methods:
A total of 460 adults (ages 20–55) were recruited for a cross-sectional study. Participants were stratified into two groups: those with SCH (n=122) and euthyroid controls (n=338). Thyroid function was assessed using serum TSH, fT4, and anti-thyroid peroxidase antibodies. Sleep quality was evaluated using the Pittsburgh Sleep Quality Index (PSQI) and Insomnia Severity Index (ISI). Anxiety and depression symptoms were controlled for using the Hospital Anxiety and Depression Scale (HADS). Multivariate linear regression was applied to identify independent associations.

Results:
Patients with SCH had significantly higher mean PSQI scores (8.3 ± 2.1) compared to euthyroid controls (5.9 ± 1.7, p < 0.001), indicating poorer sleep quality. ISI scores also indicated more severe insomnia symptoms in the SCH group (p = 0.004). After adjusting for age, sex, BMI, and mood disorders, SCH remained independently associated with poor sleep quality (β = 0.41, p < 0.01).

Conclusion:
Subclinical hypothyroidism is significantly associated with reduced sleep quality and increased insomnia symptoms. Screening for thyroid dysfunction in patients with unexplained sleep disturbances may improve clinical outcomes and guide treatment strategies.