## 3 Results
### Vitamin D and Clinical Associations in the Studied Population
\begin{table}
\begin{tabular}{l c} \hline \hline
**Variable** & \(p\) \\ \hline Gender, female & 0.73 \\ Raynaud’s present & 1.0 \\ Joint contractures & 0.56 \\ Lung fibrosis (HRTC) & 0.21 \\ Esophageal symptoms (dysphagia, reflux) & 0.07 \\ Dyspnea (\(\geq\)NYHA 2) & 0.21 \\ Digital ulcers & 0.77 \\ Joint synovitis & 1.0 \\ Muscle weakness & 0.62 \\ Telangetasia & 0.80 \\ Palpitations & 0.62 \\ Arterial hypertension & 0.002 \\ Intestinal symptoms (diarrhea, bloating, constipation) & 1.0 \\ Gastric symptoms (early satiety, vomiting) & 1.0 \\ Muscle atrophy & 0.26 \\ Restrictive defect (VC \(<\) 80\%) (\(n\) = 45) & 0.50 \\ Proteinuria & 0.18 \\ Conduction blocks & 0.30 \\ Diastolic dysfunction & 0.73 \\ Systolic dysfunction (contractility) & 0.08 \\ Pulmonary hypertension (echocardiography) & 0.71 \\ CK-elevation & 0.73 \\ Tendon friction rubs & 1.0 \\ Renal crisis & 1.0 \\ \hline NYHA—New York Heart Association (NYHA) Functional Classification of heart failure, VC—vital capacity, CK—reatinine kinase. & \\ \end{tabular}
\end{table} 
Table 2: Associations between clinical characteristics of SSc and vitamin D deficiency. Two-sided \(p\) values from the [PERSON]’s exact test are presented. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{3}{c}{**25(OHD)D3 Deficiency**} & \multicolumn{3}{c}{**25(OHD3 \textgreater{} 20 ng/mL} \\ \hline  & **Mean** & **SD** & **Mean** & **SD** & \(p\) \\ \hline Age, years & 56.1 & 12.5 & 51.6 & 14.3 & 0.3 \\ Disease duration since [PERSON] onset, y & 11.3 & 9.5 & 12.9 & 9.9 & 0.42 \\ Disease duration since the diagnosis, y & 6.0 & 7.6 & 7.9 & 9.9 & 0.59 \\ ESR, mm/h & 17.8 & 14.6 & 19.0 & 16.5 & 0.61 \\ CRP, mg/L & 4.2 & 5.8 & 2.0 & 3.4 & 0.035 \\ Serum creatinine, umol/L & 86.2 & 34.9 & 81.1 & 14.1 & 0.90 \\ eGFR CKD-EPI, mL/min/1.73 m\({}^{2}\) & 90.5 & 14.9 & 93.3 & 12.2 & 0.61 \\ mRS 1 & 14.3 & 9.5 & 11.8 & 6.0 & 0.47 \\ LVEF & 61.4 & 7.2 & 62.3 & 4.9 & 0.79 \\ FVC (\%predicted) (\(n\) = 39) & 87.8 & 17.7 & 91.6 & 23.9 & 0.62 \\ \hline \hline \end{tabular} \({}^{\dagger}\) The median modified Rodnan skin score in patients with vitamin D deficiency was 11.5 (1 st-3 rd quartile: 7.5–21.5) vs. 11.0 (7.5–15.5) in participants without deficiency. CRP—C-reactive protein, ESR—erythrocyte sedimentation rate, FVC—focred vital capacity, LVEF—left-ventricular ejection fraction, mRSS—modified Rodnan skin score, eGFR CKD–EPI—estimated glomerular filtration rate according to CKD-EPI equation.  
\end{table} 
Table 3: Associations between clinical parameters in SSc and vitamin D deficiency. Two-sided \(p\) values from the Mann–Whitney U test are presented. The essential analyses were repeated separately in limited cutaneous systemic sclerosis (lcSSc) and diffuse cutaneous systemic sclerosis (dcSSc) subgroups. The main findings included increased CRP in vitamin D-deficient patients with lcSSc (\(p\) = 0.039), and a weakly negative correlation between CRP and 25-hydroxyvitamin D3 in this subgroup (rho = \(-\)0.30, \(p\) = 0.039). Additionally, lcSSc analysis of two-way tables revealed a positive association of vitamin D deficiency with arterial hypertension (\(p\) = 0.029), and a possible relationship between vitamin D deficiency and esophageal symptoms of SSc (\(p\) = 0.055). In dcSSc, mRSS negatively correlated with 25-hydroxyvitamin D3 (rho = \(-\)0.52, \(p\) = 0.020). There was a clear link between vitamin D deficiency and lung fibrosis in dcSSc patients (\(p\) = 0.011), with all the deficient patients presenting pulmonary fibrosis, compared with approximately half of those without the deficiency. Further research may focus on