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Introduction: Vitamin D deficiency, a reversible cause of osteoporosis, is increasingly prevalent, showing varying degrees of severity that are notably pronounced among the growing population of multimorbid elderly patients. Given that the aging pancreas undergoes senescent processes leading to impaired function—which negatively impacts enteral vitamin D absorption and, consequently, elderly bone metabolism—a specific diagnostic and treatment approach is crucial. Our study aimed to determine the prevalence of vitamin D deficiency and exocrine pancreatic insufficiency (EPI) in orthogeriatric patients. We also evaluated differences in vitamin D deficiency severity between patients with normal and impaired pancreatic function. Furthermore, a short-term monitoring of vitamin D level increases after 12 days of substitution therapy in both groups aimed to inform osteoanabolic therapy for specific high-fracture-risk patients, assessing the influence of pancreatic function on substitution efficacy. Methods: We conducted a retrospective, monocentric cohort study, evaluating data from all patients hospitalized with manifest osteoporosis in an orthogeriatric department during a six-month spring/summer period. Demographic data, relevant comorbidities, the type of fracture, the amount of faecal elastase 1 (CALEX^® Cap Bühlmann), and the serum levels of 25-hydroxyvitamin D (25(OH)D) were assessed. Results: We found a high prevalence (70.6%) of vitamin D deficiency (25(OH)D < 30 µg/L) among all orthogeriatric patients. Of these, 16% met the criteria for mild to severe EPI. The group with normal exocrine pancreatic function showed a higher average vitamin D value, and their increase in vitamin D levels following short-term substitution was up to 100% greater compared to the group with impaired pancreatic function. Notably, 69% of women and 20% of men met the therapeutic threshold for specific osteoanabolic osteoporosis therapy, even without a T-score. Conclusions: Our findings reveal a very high prevalence of vitamin D deficiency and a high prevalence of EPI in orthogeriatric patients. Those with impaired exocrine pancreatic function exhibit lower baseline vitamin D levels and a diminished capacity for vitamin D absorption during short-term monitoring. These results have significant clinical implications for osteoporotic therapy, given that a substantial proportion of patients, particularly women, meet the criteria for specific osteoanabolic treatment. Full article

This study proposed a mechanochemical activation strategy using ethanol-diisopropanolamine (EDIPA) to improve the grindability and hydration reactivity of basic oxygen furnace slag (BOFS), aiming for its large-scale industrial utilization. The incorporation of EDIPA significantly refined the particle size distribution and reduced the repose angle. As a result, the compressive strength of BOFS paste increased by 25.4 MPa at 28 d with only 0.08 wt.% EDIPA. Conductivity tests demonstrated that EDIPA strongly complexes with Ca²⁺, Al³⁺, and Fe³⁺, facilitating the dissolution of active mineral phases, such as C₁₂A₇ and C₂F, and accelerating hydration reactions. XRD and TG analyses confirmed that the incorporation of EDIPA facilitated the formation of Mc (C₄(A,F)ČH₁₁) and increased the content of C-S-H, both of which contributed to microstructural densification. Microstructural observations further revealed that EDIPA refined Ca(OH)₂ crystals, increasing their specific surface area from 4.7 m²/g to 35.2 m²/g. The combined effect of crystal refinement and enhanced hydration product formation resulted in reduced porosity and improved mechanical properties. Overall, the results demonstrated that EDIPA provided an economical, effective, and scalable means of activating BOFS, thereby promoting its high-value utilization in low-carbon construction materials. Full article

In response to the growing demand for clean-label preservatives, this study investigates the potential of Laetiporus sulphureus, an edible polypore mushroom, as a multifunctional additive in cooked sausages. The ethanolic extract of L. sulphureus (LsEtOH) was evaluated for its chemical composition, antioxidant capacity, and antimicrobial activity. Leucine (12.4 ± 0.31 mg/g d.w.) and linoleic acid (68.6%) were identified as the dominant essential amino acid and fatty acid. LsEtOH exhibited strong antioxidant activity, with IC₅₀ values of 215 ± 0.05 µg/mL (DPPH•), 182 ± 0.40 µg/mL (NO•), and 11.4 ± 0.01 µg/mL (OH•), and showed a selective inhibition of Gram-positive bacteria, particularly Staphylococcus aureus (MIC/MBC: 0.31/0.62 mg/mL). In cooked sausages treated with 0.05 mg/kg of LsEtOH, lipid peroxidation was reduced (TBARS: 0.26 mg MDA/kg compared to 0.36 mg MDA/kg in the control), microbial growth was suppressed (33.3 ± 15.2 CFU/g in the treated sample compared to 43.3 ± 5.7 CFU/g in the control group), and color and pH were stabilized over 30 days. A sensory evaluation revealed minor flavor deviations due to the extract’s inherent aroma. Encapsulation and consumer education are recommended to enhance acceptance. This is the first study to demonstrate the efficacy of L. sulphureus extract as a natural preservative in a meat matrix, supporting its application as a clean-label additive for shelf life and safety improvement. Full article

Based on the limited hepatic hydroxylation efficiency of dietary VD3 in teleosts and the superior bioavailability of its metabolite, 25(OH)D3, this study investigated the regulatory mechanisms of dietary 25(OH)D3 supplementation in yellow catfish—an economically significant species lacking prior nutritional data on this metabolite. A total of 360 fish were divided into three groups—control (basal diet), VD3 (2500 IU/kg VD3), and 25(OH)D3 (2500 IU/kg 25(OH)D3)—and fed for 8 weeks. Compared to the control, both supplemented groups showed elevated superoxide dismutase (SOD), total antioxidant capacity (T-AOC), catalase (CAT), and transforming growth factor-β (TGF-β) activities, alongside reduced malondialdehyde (MDA), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) levels. The 25(OH)D3 group exhibited higher T-AOC and CAT activities and lower TNF-α than the VD3 group. Metabolomic and transcriptomic analyses identified 65 differentially expressed metabolites (DEMs) and 3515 differentially expressed genes (DEGs). Enrichment analysis indicated that the DEMs (e.g., indole compounds, organic acids, aldosterone, L-kynurenine) and DEGs (pgd, mthfr, nsdhl, nox5, prdx2, mpx, itih2, itih3, eprs1) that were highly and significantly expressed in the 25(OH)D3 group were primarily associated with antioxidant defense and inflammatory responses. Dietary 25(OH)D3 was more effective than VD3 in promoting antioxidant capacity and modulating inflammation in yellow catfish. Full article

Background/Objective: In patients with acute lymphoblastic leukemia (ALL), it has been demonstrated that the treatment has a negative effect on bone health. The n-3 polyunsaturated fatty acids (LCPUFAs-ω3) may attenuate bone resorption. We evaluated the effects of LCPUFAs-ω3, vitamin D, and calcium supplementation on bone turnover markers and changes in vitamin D concentrations during 6 weeks of supplementation and during 6 weeks of post-intervention follow-up in pediatric patients with ALL. Methods: Thirty-six pediatric patients with ALL were randomly assigned to the ω-3VDCa group (100 mg/kg/d LCPUFAs-ω3 + 4000 IU vitamin D + 1000 mg calcium) or the VDCa group (4000 IU vitamin D + 1000 mg calcium) for 6 weeks. Blood samples were collected to determine 25(OH)D, PTH, ICTP, and TRAP-5b (biomarkers of bone resorption) and osteocalcin (OC, a biomarker of bone production) levels at baseline, 6 weeks, and 12 weeks after supplementation. The 25(OH)D analysis was performed using ultra-high-performance liquid chromatography coupled to a mass spectrometer, and PTH and bone turnover markers were measured by ELISA. Results: The 25(OH)D concentration increased in both groups (ω3VDCa group: 19.4 ng/mL vs. 44.0 ng/mL, p < 0.0001; VDCa group: 15.3 ng/mL vs. 42.8 ng/mL, p = 0.018) and remained significantly higher at 12 weeks. At 12 weeks, ICTP showed lower concentrations in the ω-3VDCa group than in the VDCa group (0.74 ng/mL vs. 1.05 ng/mL, p = 0.024). Conclusions: Combined omega-3 and 4000 IU vitamin D supplementation for 6 weeks had a positive effect on bone health, as indicated by serum ICTP, with no effect on serum 25(OH)D levels over vitamin D supplementation alone. Full article

Hydrogen energy is a pivotal carrier for achieving carbon neutrality, requiring green and efficient production via water electrolysis. However, the anodic oxygen evolution reaction (OER) involves a sluggish four-electron transfer process, resulting in high overpotentials, while the prohibitive cost and complex preparation of precious metal catalysts impede large-scale commercialization. In this study, we develop a FeCo-based bimetallic deep eutectic solvent (FeCo-DES) as a multifunctional reaction medium for engineering a three-dimensional (3D) coral-like FeOOH-Co₂(OH)₃Cl/NF composite via a mild one-step impregnation approach (70 °C, ambient pressure). The FeCo-DES simultaneously serves as the solvent, metal source, and redox agent, driving the controlled in situ assembly of FeOOH-Co₂(OH)₃Cl hybrids on Ni(OH)₂/NiOOH-coated nickel foam (NF). This hierarchical architecture induces synergistic enhancement through geometric structural effects combined with multi-component electronic interactions. Consequently, the FeOOH-Co₂(OH)₃Cl/NF catalyst achieves a remarkably low overpotential of 197 mV at 100 mA cm⁻² and a Tafel slope of 65.9 mV dec⁻¹, along with 98% current retention over 24 h chronopotentiometry. This study pioneers a DES-mediated strategy for designing robust composite catalysts, establishing a scalable blueprint for high-performance and low-cost OER systems. Full article

Alkaline electrolytic water hydrogen generation, a key driver in the growth of hydrogen energy, heavily relies on high-efficiency and high-purity ion exchange membranes. In this study, three-dimensional (3D) wrinkled reduced graphene oxide (WG) nanosheets obtained through a simple thermal reduction process and two-dimensional (2D) graphene oxide act as building blocks, with ethylenediamine as a crosslinking stabilizer, to construct a unique 3D/2D 2 nm-tunneling structure between the GO and WG sheets through via an amide connection at a WG/GO ratio of 1:1. Here, the wrinkled graphene (WG) undergoes a transition from two-dimensional (2D) graphene oxide (GO) into three-dimensional (3D) through the adjustment of surface energy. By increasing the interlayer spacing and the number of ion fluid channels within the membranes, the E-W/G membrane has achieved the rapid passage of hydroxide ions (OH⁻) and simultaneous isolation of produced gas molecules. Moreover, the dense 2 nm nano-tunneling structure in the electrolytic water process enables the E-W/G membrane to attain current densities >99.9% and an extremely low gas crossover rate of hydrogen and oxygen. This result suggests that the as-prepared membrane effectively restricts the unwanted crossover of gases between the anode and cathode compartments, leading to improved efficiency and reduced gas leakage during electrolysis. By enhancing the purity of the hydrogen production industry and facilitating the energy transition, our strategy holds great potential for realizing the widespread utilization of hydrogen energy. Full article

Experimental and theoretical studies were applied to investigate the adsorption properties of testagen (KEDG) peptide on copper surfaces in sodium chloride solution and, implicitly, its inhibition efficiency (IE) on metal corrosion. The tetrapeptide synthesized from the amino acids lysine (Lys), glutamic acid (Glu), aspartic acid (Asp), and glycine (Gly), named as H-Lys-Glu-Asp-Gly-OH, achieved an inhibition efficiency of around 86% calculated from electrochemical measurements, making KEDG a promising new copper corrosion inhibitor. The experimental data were best fitted to the Freundlich adsorption isotherm. The standard free energy of adsorption ($\mathsf{\Delta }{\mathrm{G}}_{\mathrm{a}\mathrm{d}\mathrm{s}}^{\mathrm{o}}$) reached the value of −30.86 kJ mol⁻¹, which revealed a mixed action mechanism of tetrapeptide, namely, chemical and physical spontaneous adsorption. The copper surface characterization was performed using optical microscopy and SEM/EDS analysis. In the KEDG presence, post-corrosion, SEM images showed a network surface morphology including microdeposits with an acicular appearance, and EDS analysis highlighted an upper surface layer consisting of KEDG, sodium chloride, and copper corrosion compounds. The computational study based on DFT and Monte Carlo simulation confirmed the experimental results and concluded that the spontaneous adsorption equilibrium establishment was the consequence of the contribution of noncovalent (electrostatic, van der Waals) interactions and covalent bonds. Full article

Ethanol upgrading via catalytic C–C coupling, commonly known as the Guerbet reaction, offers a sustainable route to produce 1-butanol, a high-performance biofuel. To address gaps in the mechanistic understanding of the catalytic reaction, we investigated the process involving a fixed-bed reactor, operated at 275–325 °C, 21 bar, and weight hourly space velocities of 0.25–2.5 g_EtOH/(g_cat·h), using helium as a carrier gas, with a 5:1 He/EtOH molar ratio. The catalyst was a MgO–Al₂O₃ mixed oxide (Mg/Al = 2:1), derived from a hydrotalcite precursor. A detailed kinetic model was developed, encompassing 15 species and 27 reversible steps (10 sorption and 17 reaction steps), within a 1+1D sorption–reaction–transport framework. Four C₄-forming pathways were included: aldol condensation to form crotonaldehyde, semi-direct coupling to form butyraldehyde and crotyl alcohol, and direct coupling to form 1-butanol. To avoid overfitting, Arrhenius parameters were grouped by reaction type, resulting in sixty rate parameters and one active site-specific density parameter. The optimized model achieved high accuracy, with an average prediction error of 1.44 times the experimental standard deviation. The mechanistic analysis revealed aldol condensation as the dominant pathway below 335 °C, with semi-direct coupling to crotyl alcohol prevailing above 340 °C. The resulting model provides a robust framework for understanding and predicting complex reaction networks in ethanol upgrading systems. Full article

Background and Objectives: Type 2 diabetes mellitus (T2DM) is associated with subclinical cardiovascular changes, such as increased arterial stiffness and myocardial dysfunction. Vitamin D deficiency has been recognized as a potential contributing factor to vascular disease; however, its impact on early cardiac changes associated with T2DM remains poorly understood. Our aim was to evaluate the association between serum levels of 25-hydroxyvitamin D3 [25(OH)D3], arterial stiffness, and left ventricular global longitudinal strain (LV GLS) in patients with T2DM who do not have a clinically evident cardiovascular disease. Material and methods: This cross-sectional study evaluated the carotid intima–media thickness (IMT), aortic pulse wave velocity (PWVao), LV GLS, and serum 25(OH)D3 levels in patients diagnosed with T2DM (n = 65) compared to healthy control subjects (n = 55). Independent predictors of arterial stiffness were identified by a multivariate logistic regression analysis. Results: Patients with T2DM showed a significant increase in IMT and PWVao, a reduction in LV GLS, and low levels of 25(OH)D3 compared to subjects in the control group (all p < 0.05). Both vitamin D deficiency and T2DM were found to be independently associated with an increased arterial stiffness, with odds ratios of 2.4 and 4.8, respectively. A significant inverse relationship was identified between 25(OH)D3 levels and markers of arterial stiffness, as well as LV GLS, suggesting a possible association between the vitamin D status and the early onset of cardiovascular dysfunction. Conclusions: Patients with T2DM show early signs of heart and blood vessel problems, even with an ejection fraction that remains within normal limits. There is a significant correlation between vitamin D deficiency and increased arterial stiffness, along with impaired LV GLS, indicating its possible involvement in cardiovascular complications associated with diabetes. These findings support the utility of integrating vascular, myocardial, and vitamin D assessments in early cardiovascular risk stratification for T2DM patients. Full article

Organic acids could act as retarders in magnesium oxysulfide (MOS) systems, not only delaying setting and improving fluidity but also enhancing compressive strength and water resistance. These effects are generally attributed to both the presence of H⁺ ions and anion chelation. However, the enhancement efficiency of different organic acids in MOS systems varies significantly due to differences in their molecular structures. To determine the underlying mechanism, this study comparatively investigated the effects of amino trimethylene phosphonic acid (ATMP) and tartaric acid (TA) on the setting time, fluidity, compressive strength, and water resistance of the MOS system, with the two additives incorporated at mole ratios to MgO ranging from 0.002 to 0.006. The mechanism behind it was revealed by discussion on the hydration heat, hydrates, and pH value. Results showed that both ATMP and TA could effectively improve the fluidity, delay the setting process, and enhance the mechanical properties, including strength and water resistance. At a mole ratio of 0.006, the incorporation of ATMP increased the 28 d compressive strength and the softening coefficient by 214.12% and 37.29%, respectively, compared with the blank group. In contrast, under the same dosage, TA led to an increase of 55.13% in the 28 d strength and 22.03% in the softening coefficient. Furthermore, hydration heat, product analysis, and pH measurements indicated that both ATMP and TA inhibited hydration during the initial hours but promoted hydration at later stages. The potential reason could be divided into two aspects: (1) H⁺ ions from ATMP and TA suppressing the formation of Mg(OH)₂; (2) anion chelation with Mg²⁺ in the liquid phase, leading to a supersaturated solution with higher saturation, which further hindered Mg(OH)₂ formation and facilitated the later development of 5Mg(OH)₂·MgSO₄·7H₂O (517 phase). By contrast, under the same mole dosage of H⁺ or anions, the enhancement in compressive strength as well as the water resistance is superior when using ATMP. This was owing to its stronger chelating ability of ATMP, which more effectively inhibited Mg(OH)₂ formation and then promoted the formation of the 517 phase. These findings confirm that the chelating ability of anions exerts an important impact on the retarding effect as well as the enhancement of strength in MOS systems. Full article

Background/Objectives: Serum 25-hydroxyvitamin D (25(OH)D) concentrations are decreased with metabolic syndrome (MetSy), and low serum 25(OH)D concentrations are associated with poor outcomes following anterior cruciate ligament (ACL) reconstruction (ACLR). It is unknown whether serum 25(OH)D concentrations are decreased in patients with MetSy following ACLR. The purpose of this study was to investigate whether serum 25(OH)D concentrations are decreased with MetSy following ACLR. Methods: This retrospective case–control study consisted of patients (≥18 years) who underwent ACLR. MetSy was defined as meeting any three of the five criteria (cases): (1) body mass index ≥ 30 kg/m², (2) triglycerides ≥ 150 mg/dL, (3) HDL < 40 mg/dL in men and <50 mg/dL in women, (4) systolic blood pressure ≥ 130 mmHg or diastolic blood pressure ≥ 85 mmHg, or (5) estimated (from hemoglobin A1c% [HbA1c]) fasting glucose ≥ 100 mg/dL. Participants without MetSy (meeting <3 criteria) served as controls. The first blood lipid, HbA1c, and 25(OH)D assessed ≥90 d after ACLR were included in this study. Results: The final analysis consisted of 219 patients (cases (with MetSy), n = 84; controls (without MetSy), n = 135). Serum 25(OH)D was significantly (p < 0.01) decreased (15.8%) in cases (mean [SD]; 25.1 [11.3] ng/mL) compared to controls (29.8 [14.8] ng/mL). An increasing number of MetSy components was associated with a decreased prevalence of vitamin D sufficiency (p < 0.01). Conclusions: We conclude that serum 25(OH)D concentrations are significantly lower with MetSy. These preliminary findings could provide justification for assessing serum 25(OH)D following ACLR in patients with MetSy and assist with risk stratification. Full article

Background: The most common female endocrinopathy is polycystic ovary syndrome (PCOS), affecting 10–20% of women of reproductive age. It is associated with a wide range of hormonal and biochemical abnormalities and long-term metabolic and cardiovascular risks. It is characterized by infertility due to chronic anovulation, hyperandrogenism, polycystic ovarian morphology, and is often associated with insulin resistance (IR) and obesity. Hyperinsulinemia further increases androgen production and reduces sex hormone-binding globulin (SHBG) levels, thereby aggravating symptoms. In addition, vitamin D deficiency is often present in PCOS patients, and increasing evidence suggests that it may also be associated with insulin resistance and hyperandrogenism. Objective: This study aimed to evaluate the relationships between insulin resistance, vitamin D deficiency, body mass index (BMI), and androgen levels in women with PCOS. Method: A cross-sectional study was conducted in which data from 195 women diagnosed with PCOS and not yet receiving therapy at a gynecologic endocrinology unit of a university-based tertiary clinical center, between 2019 and 2024, were analyzed. The parameters recorded were age, body mass index (BMI), 25(OH) vitamin D levels, androgen hormone levels (testosterone, androstenedione), glucose-insulin responses during a 3-point oral glucose tolerance test (OGTT). Statistical analyses, including linear regression, Pearson, and Spearman correlation tests were used to assess associations between variables. Results: The mean age of the patients was 24.8 years (18–42), and the mean BMI was 30.6 kg/m² (17–51). Vitamin D deficiency was observed in 84.1% of patients, hyperandrogenism in 45.8%, and insulin resistance in 44.5%. A significant inverse correlation was found between BMI and vitamin D levels (r = −0.31, p =< 0.01) indicating that higher BMI is associated with lower vitamin D status. Similarly, BMI also showed a significant negative correlation with SHBG levels (r = –0.45, p < 0.01), suggesting that increasing body weight is linked to reduced SHBG concentrations. In addition, BMI was significantly positively correlated with 2 h insulin levels (r = 0.43, p =< 0.01) and with testosterone levels (r = 0.21, p = 0.01). These findings suggest that increased adiposity intensifies insulin resistance and is linked to both vitamin D deficiency and elevated androgen levels. Moreover, the combination of hyperinsulinemia and low vitamin D further disrupts hormonal balance by promoting ovarian androgen production and decreasing SHBG levels, thereby increasing the bioavailability of testosterone. A significant inverse correlation was found between vitamin D levels and 2 h insulin levels (r = −0.28, p =< 0.01), indicating that lower vitamin D status is associated with increased insulin resistance. Furthermore, 2 h insulin levels showed a significant positive correlation with testosterone levels (r = 0.32, p =< 0.01), suggesting that greater insulin resistance is linked to higher androgen production. Additionally, vitamin D levels were inversely correlated with testosterone (r = −0.18, p = 0.02), demonstrating that a lower vitamin D status may further contribute to the hyperandrogenic environment. Vitamin D levels also showed a significant positive correlation with SHBG concentrations (r = 0.29, p < 0.01), indicating that a higher vitamin D status may be associated with increased SHBG levels. In contrast, 2 h insulin levels were inversely correlated with SHBG (r = −0.43, p < 0.01), reflecting the suppressive effect of hyperinsulinemia on SHBG production. Conclusions: Insulin resistance, BMI, and vitamin D deficiency are closely related to each other and to the severity of PCOS, which is confirmed by the correlations with androgen levels. The revealed relationships draw attention to the special importance of vitamin D supplementation and the correction of carbohydrate metabolism in alleviating the symptoms of the disease and reducing long-term health risks. Full article

Background/Objectives: Gallic acid, a natural phenolic compound, was used as a crosslinking agent to achieve protein–polyphenol conjugation under alkaline conditions, presenting an innovative approach to stabilize gelatin. Methods: The formulated inks were evaluated for their rheological properties and 3D printing performance. Once the scaffolds were printed, physicochemical properties were assessed by color changes and FTIR. Additionally, three different post-processing methods were studied to avoid toxicity: incubation in PBS, incubation in NaOH followed by PBS neutralization, and incubation in HCl followed by PBS neutralization. Results: The inks exhibited shear-thinning behavior with self-supporting capacity after extrusion, indicating their suitability for use as inks in 3D printing. After printing, changes in color and in the amide I band/amide II band ratio were observed due to alkaline oxidation, confirming the gelatin crosslinking. Among the tested treatments, incubation in PBS or NaOH followed by neutralizing with PBS proved to be the most suitable for obtaining cytocompatible scaffolds. The mechanical properties demonstrated the suitability of the proposed crosslinking systems for creating scaffolds. Conclusions: This strategy confirms that gallic acid-mediated crosslinking under alkaline conditions enables the fabrication of cytocompatible and mechanically stable gelatin-based scaffolds, making them suitable for tissue engineering. Full article

Objectives: This study aimed to investigate both the linear and non-linear associations between serum 25-hydroxyvitamin D [25(OH)D] levels and serum uric acid concentrations in Korean adults, with a particular focus on the vitamin D-insufficient range (<30 ng/mL), and to explore the potential metabolic implications of this relationship. Methods: Using data from the Korea National Health and Nutrition Examination Survey (KNHANES), we analyzed 10,864 adults aged 19 years and older. Serum vitamin D levels were categorized into quartiles (Q1–Q4), and their relationships with uric acid concentrations were examined using Pearson correlation, analysis of variance (ANOVA), and restricted cubic spline regression. Multivariate models were adjusted for potential confounders including age, sex, body mass index (BMI), kidney function, chronic disease status, and macronutrient intake. Results: In unadjusted analysis, a statistically significant but weak negative correlation was observed between serum 25(OH)D and uric acid levels (Pearson’s r = −0.092, p < 0.001). However, in multivariate regression adjusting for confounders, a weak positive association emerged. Restricted cubic spline analysis revealed significant positive associations in the lower quartiles (Q1–Q3), with the strongest association in Q3 (β = 0.769, 95% CI: 0.34–1.19, p < 0.001). No significant association was observed in the highest quartile (Q4). Conclusions: Serum vitamin D and uric acid concentrations show a non-linear relationship, with a significant positive association within the vitamin D-insufficient range (<30 ng/mL). These findings provide new insights into the potential metabolic role of vitamin D and highlight the need for longitudinal and interventional studies to clarify causality and clinical significance. Full article