Abstract
BACKGROUND: Osteoarthritis (OA) is a common chronic degenerative joint disease globally. While sleep-related factors are linked to its pathogenesis, the specific association and nonlinear characteristics between sleep midpoint (the midpoint of the sleep cycle) and OA remain unclear. METHODS: Data for this study were obtained from the National Health and Nutrition Examination Survey (NHANES 2015-2020). Sleep midpoint was calculated from self-reported weekday bedtime and wake-up time. Restricted cubic spline (RCS) models analyzed the relationship between sleep midpoint and OA, adjusted for demographic, lifestyle, and clinical covariates. Subgroup analyses and propensity score matching verified result robustness. RESULTS: A total of 7640 participants were included in this study, of whom 977 had OA. RCS revealed a "J-shaped" association with an inflection point at 2:30 AM. No significant association was found for sleep midpoint < 2:30 AM (OR = 0.95, 95% CI = 0.88-1.02). For sleep midpoint ≥ 2:30 AM, each 30-min delay was associated with an 8% increased OA prevalence (OR = 1.08, 95%CI = 1.00-1.18). Subgroup and matched analyses confirmed robustness. CONCLUSIONS: Our study results indicate that in a representative sample of US adults, a delayed sleep midpoint (≥ 2:30 AM) is independently associated with OA, suggesting that a delayed sleep midpoint beyond 2:30 AM is linked to a higher prevalence of OA. This highlights the potential role of sleep midpoint in OA prevention and management. Key Points • Sleep midpoint shows a nonlinear association with osteoarthritis prevalence, with an inflection around 02:30 AM. • After approximately 02:30 AM, each 30-min delay in sleep midpoint is associated with ~ 8% higher adjusted odds of osteoarthritis, independent of demographics, lifestyle factors, comorbidities, and sleep duration. • Results are consistent across subgroups and remain robust in propensity score-matched and sensitivity analyses using survey weighted, nationally representative US data. • Sleep timing is modifiable, indicating a practical target for risk reduction that warrants prospective and interventional evaluation.