Nonlinear association between sleep duration and thyroid hormone levels in patients with thyroid cancer

Sleep duration is a modifiable behavioral factor that may influence endocrine regulation, yet its specific association with thyroid function among thyroid cancer patients has not been fully elucidated. Thyroid hormones—including thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4)—are key regulators of metabolism and are sensitive to sleep-related circadian changes. This study included 1 204 participants from a Chinese clinical thyroid cancer cohort (2022–2024). Sleep duration was categorized as short (≤ 6 h), normal (7–8 h), and long (≥ 9 h). Baseline characteristics were compared using χ2 and ANOVA tests (Table 1). Multivariable linear regression models evaluated associations between sleep duration and serum TSH, T3, and T4 levels, adjusting for demographic and clinical covariates. Piecewise linear regression and locally weighted scatterplot smoothing (LOESS) curves assessed nonlinear dose–response patterns, while gender-stratified analyses explored effect modification. Participants with short or long sleep had significantly altered thyroid hormone profiles compared with those reporting 7–8 h of sleep. In fully adjusted models, short sleep was associated with higher TSH (β = 0.48, 95% CI 0.40–0.56; p < 0.001) and lower T3 (β = –0.045, 95% CI –0.061–; –0.029; p < 0.001) and T4 (β = –0.318, 95% CI –0.437–; –0.198; p < 0.001). Long sleep showed a weaker but consistent trend (TSH β = 0.53, 95% CI 0.44–0.62; p < 0.001). Piecewise regression identified a threshold near 7 h, confirming a U-shaped relationship between sleep duration and thyroid hormones. LOESS curves visually demonstrated this nonlinear pattern, and gender-stratified analyses revealed sex-specific differences in the association between sleep duration and thyroid hormones. Both insufficient and excessive sleep were associated with dysregulated thyroid hormone levels in thyroid cancer patients, indicating a nonlinear U-shaped relationship with an optimal sleep duration around 7 h.