Objective To investigate the relationship between serum vitamin D levels and benign prostatic hyperplasia (BPH) in patients with metabolic syndrome (MetS).

Methods Based on the National Health and Nutrition Examination Survey database, this study systematically screened data from 2001 to 2008 and included patients meeting the MetS diagnostic criteria of the National Cholesterol Education Program. Patients were grouped according to quartiles of serum vitamin D levels, with weighted χ² test used for baseline characteristic comparisons between groups. Subsequently, stratified and weighted multivariate logistic regression was employed to assess the correlation and its association strength with BPH, followed by restricted cubic spline analysis to validate the dose-response relationship.

Results A total of 1 816 patients with MetS were enrolled, including 510 BPH patients and 1306 non-BPH patients. The patients were grouped by serum vitamin D quartiles and analyzed using weighted multivariate logistic regression, the results demonstrated that, using the high vitamin D group (Q4) as reference, the low vitamin D group (Q1) had a 3.541-fold increased risk of BPH (Model 1, OR: 3.541, 95%CI: 2.273–5.522, P for trend ＜0.01). After adjusting for multiple covariates, the BPH risk in Q1 remained significantly elevated compared to Q4, with increases of 4.172-fold and 4.255-fold, respectively (Model 2, OR: 4.172, 95%CI: 2.718–6.453, P for trend ＜0.01; Model 3, OR: 4.255, 95%CI: 2.778–6.545, P for trend ＜ 0.01). The results of restricted cubic spline plot further indicated a significant linear negative association between vitamin D level and BPH risk (P for nonlinearity ＞ 0.05).

Conclusions Low vitamin D levels may be associated with a higher BPH risk in patients with MetS, suggesting that clinicians should emphasize vitamin D supplementation in male MetS patients.