## 3 Results
### Vitamin D and Clinical Associations in the Studied Population  
We assessed several clinical and laboratory features using the EUSTAR methodology and found that patients with vitamin D deficiency presented a significantly higher prevalence of arterial hypertension (62.5% vs. 21.9%, \(p\) = 0.0021). No other associations were found, as presented in Table 2. \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Variable** & **Mean (or \%)** & **SD** \\ \hline Gender, female, \% & 85\% & \\ Limited cutaneous systemic sclerosis & 66\% & \\ Diffuse cutaneous systemic sclerosis & 29\% & \\ Polymyositis-scleroderma overlap syndrome & 4\% & \\ Age, years & 53.8 & 13.5 \\ Disease duration since [PERSON], years & 12.1 & 9.7 \\ Disease duration since diagnosis, years & 7.0 & 8.8 \\ ESR, mm/h & 18.4 & 15.5 \\ CRP, mg/L & 3.1 & 4.8 \\ Serum creatinine, umol/L & 83.7 & 26.6 \\ eGFR CKD-EPI, mL/min/1.73 m\({}^{2}\) & 91.9 & 13.6 \\
25(OH)D3, ng/mL & 21.6 & 10.0 \\ Vitamin D deficiency [25(OH)D3 \textless{} 20\textgreater{} mL], \% & 50\% & \\ mRSS score 1 & 13.0 & 8.0 \\ [PERSON]’s present, \% & 99\% & \\ Joint contractures, \% & 78\% & \\ Lung fibrosis (HRCT), \% & 78\% & \\ Esophageal symptoms (dysphagia, reflux), \% & 66\% & \\ Dyspnea (\(\geq\)NYHA 2), \% & 62\% & \\ Digital ulcers, \% & 60\% & \\ Joint synovitis, \% & 49\% & \\ Muscle weakness, \% & 48\% & \\ Telangiecasia, \% & 47\% & \\ Palpitations, \% & 46\% & \\ Arterial hypertension, \% & 42\% & \\ Intestinal symptoms (diarrhea, bloating, constipation), \% & 31\% & \\ Gastric symptoms (early satiety, vomiting), \% & 29\% & \\ Muscle atrophy, \% & 26\% & \\ Restrictive defect (VC \textless{} 80\%) (\(n\) = 45), \% & 24\% & \\ Systolic dysfunction (contractility), \% & 16\% & \\ Conduction blocks, \% & 16\% & \\ Diastolic dysfunction, \% & 16\% & \\ CK-elevation, \% & 14\% & \\ Pulmonary hypertension (echocardiography),\% & 13\% & \\ Tendon friction rubs, \% & 7\% & \\ Renal crisis, \% & 2\% & \\ FVC (\%predicted) (\(n\) = 39), \% & 89.4 & 20.4 \\ LVEF, \% & 61.9 & 6.1 \\ \hline \hline \end{tabular}  
* The median modified Rodnan skin score was 11 (1 st–3 rd quartile: 7.5–16.0). SD = standard deviation, eGFR CKD-EPI—estimated glomerular filtration rate CKD-EPI equation, CRP—C-reactive protein, ESR—erythrocyte sedimentation rate, FVC—forced vital capacity, LVEF—left-ventricular ejection fraction, mRSS—modified Rodnan skin score, NYHA—New York Heart Association (NYHA) Functional Classification of heart failure.  
\end{table} 
Table 1: Characteristics of the studied population of patients with SSc. In our study group, SSc patients with vitamin D deficiency showed higher CRP levels than those without the deficiency (4.2 mg/L vs. 2.0, \(p\) = 0.035; Table 3). No difference was observed between the groups in terms of kidney function, measured by eGFR, although patients with proteinuria presented significantly lower mean vitamin D levels (13.7 vs. 23.0 ng/mL, \(p\) = 0.0021). We also found that mean serum 25-hydroxyvitamin D3 concentration was lower in patients with SSc-related ILD than in the rest of the SSc patients (19.5 ng/dL vs. 27.2 ng/dL, \(p\) = 0.032). An exploration of the data using the Mann-Whitney U test and the Spearman's rank-sum correlation did not allow for the identification of other clinical or laboratory factors associated with 25-hydroxyvitamin D3 serum concentrations in this group of patients with SSc, as shown in Tables 4 and 5.