Optimal serum vitamin D3 levels are associated with lower osteoarthritis risk and better overall health in US adults.

To recommend serum Vitamin D3(VD3) levels for osteoarthritis patients and susceptible populations by analyzing the dose-effect relationship between VD3 and the risk of osteoarthritis(OA) and between life's essential 8 and VD3 in OA patients. This study analyzed the National Health and Nutrition Examination Survey (NHANES) 2007-2018 cross-sectional data, excluding incomplete cases. Weighted baselines were calculated, and multiple logistic regression was used to assess the VD3-OA risk relationship. Multiple linear regression explored the VD3-LE8 score association in general and OA populations. Curve associations were modeled with restricted cubic splines, followed by subgroup and sensitivity analysis, and segmented regression based on the spline outcomes. Of 18,107 participants, OA patients had higher VD3 (76.79 nmol/L) and lower LE8 (64.70) than normal participants (65.96 nmol/L, 70.02). VD3 levels (Q1-Q4) correlated with OA risks of 9.82%-19.77%. Higher VD3 increased OA risk (Estimate = 0.006, P < 0.0001 per 1nmol/L), but RCS and segmented regression showed a U-shaped association (cutoff: 41 nmol/L). In OA patients and normals, VD3 positively correlated with LE8 (Estimate = 0.035, P < 0.001 for per 1nmol/L), with a linear RCS relationship. Sensitivity analysis confirmed these results. Our findings reveal a U-shaped association between VD3 levels and the risk of osteoarthritis (OA), while a positive association between VD3 and LE8 score. Based on these observations, we recommend maintaining moderate serum VD3 levels, for both OA-susceptible individuals and patients to optimize its overall health benefits.