Association of psychological symptoms with poor sleep quality in adults: a cross-sectional network analysis and effect modification by thyroid hormones
Psychological symptoms and poor sleep quality (PSQ) frequently co-occur and impose a substantial public health burden. This study aimed to investigate the association between psychological symptoms and PSQ, examine whether thyroid hormones modify this association, and characterize the mixed psychological -sleep -thyroid symptom network among adults undergoing routine health examinations. This study enrolled 3,694 adults who underwent routine health screening at the Health Management Center of Sichuan Provincial People’s Hospital between April 2022 and December 2025. Participants were categorized into a PSQ group and a normal control group based on their Pittsburgh Sleep Quality Index (PSQI) scores. Modified Poisson regression with robust sandwich variance estimators (HC3) was used to estimate prevalence ratios (PRs) for the association between psychological symptoms (Symptom Checklist-90, SCL-90) and PSQ. Effect modification by thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) was tested using multiplicative interaction terms in stratified and continuous-variable models. Finally, a mixed “psychological-sleep-thyroid” symptom network was constructed to calculate the expected influence and bridge strength of the nodes. After adjusting for potential confounders, participants in the highest quartile of GSI scores exhibited a 5.81-fold increased prevalence of PSQ compared to those in the lowest quartile (PR = 5.81, 95% CI: 4.86-6.95, P < 0.001). Effect modification analysis revealed that FT3 significantly modified the association between psychological symptoms and PSQ (PR for interaction per 1-unit GSI increase = 1.35, 95% CI: 1.24-1.46, P < 0.001), with the prevalence ratio increasing from 1.61 (95% CI: 1.53-1.69) in the below-median FT3 group to 2.26 (95% CI: 2.02-2.53) in the above-median FT3 group. The modifying effects of TSH and FT4 were not statistically significant in continuous models. Symptom network analysis demonstrated that depressive symptoms, anxiety, and subjective sleep quality were among the nodes with the highest expected influence. Moreover, daytime dysfunction and FT3 demonstrated substantial cross-module bridge expected influence. In this cross-sectional study, elevated psychological symptom severity was positively associated with PSQ prevalence, and this association appeared to be modified by FT3 levels. Depressive symptoms and subjective sleep quality emerged as central nodes, while daytime dysfunction and FT3 appeared to serve as key bridge nodes across psychological, sleep, and thyroid domains. Longitudinal studies are needed to clarify temporal relationships and evaluate whether targeting FT3-related pathways and daytime functioning may help reduce sleep disturbances.