Impact of Vitamin D and Outcomes of Diabetic Foot Ulcers: A Case–Control Study

Background: Vitamin D has been proposed as a potential modulator of diabetic foot ulcer (DFU) risk and healing due to its immunomodulatory and wound-healing properties. However, its independent role in DFU pathogenesis and ulcer outcomes remains unclear. Methods: This case–control, observational study included 960 patients attending a tertiary diabetic foot care clinic, of which 727 were included comprising 526 patients with DFU and 201 without DFU (non-DFU control). Serum 25-hydroxyvitamin D [25(OH)D] levels obtained at presentation were quantified and categorized into deficiency (<20 ng/mL) or absence of deficiency (>20 ng/mL), followed by subgroup analysis (severe deficiency, <12 ng/mL; deficiency, 12–20 ng/mL; insufficiency, 20–30 ng/mL; sufficiency, >30 ng/mL). Logistic regression assessed the independent association of 25(OH)D levels with DFU occurrence, adjusting for body mass index, duration of diabetes, glycated hemoglobin, retinopathy, neuropathy, and coronary artery disease (CAD)/cerebrovascular accident (CVA). Kaplan–Meier and Cox regression analyses were performed for DFU healing and long-term outcomes. Results: Median serum 25(OH)D levels were significantly lower in the DFU group than in the non-DFU group (20.1 ng/mL vs. 25.4 ng/mL, P < 0.001). Logistic regression revealed no significant association between 25(OH)D levels and DFU occurrence (odds ratio [OR] = 1.01, P = 0.280). In contrast, neuropathy (OR = 23.1, P < 0.001), CAD/CVA (OR = 8.40, P < 0.001), and retinopathy (OR = 2.76, P = 0.001) emerged as the strongest significant predictors. Serum 25(OH)D levels were not associated with DFU severity ( P = 0.860) or healing (Kaplan–Meier, P = 0.43). Cox regression confirmed no significant predictors of healing outcomes, including serum 25(OH)D levels ( P = 0.719). Conclusions: Vitamin D deficiency is prevalent in patients with DFU, but it does not corelates with occurrence, severity, or healing of foot ulcer in people with diabetes. The presence of neuropathy, retinopathy, and coronay artery disease are stronger predictors of DFU risk. These findings highlight the multifactorial nature of DFU pathogenesis and underscore the need for a multidisciplinary management approach.