Vitamin D Deficiency as a Potential Modifier of Hematological Outcomes and Vaso-Occlusive Crisis Frequency in Sickle Cell Disease: Evidence from a Sudanese Cohort

Background: Vitamin D deficiency is highly prevalent in patients with sickle cell disease (SCD) and may contribute to hematological dysregulation and increased vaso-occlusive crisis (VOC) burden. However, data from Sudan, a region with a substantial SCD burden, remain limited. This study investigated the prevalence and determinants of vitamin D deficiency and its association with hematological parameters and VOC frequency in Sudanese patients with SCD. Methods: A cross-sectional observational study was conducted among 50 patients with confirmed SCD attending a hematology outpatient clinic in Sudan. Serum 25-hydroxyvitamin D [25(OH)D] levels were measured using chemiluminescence immunoassay and categorized as deficient (<20 ng/mL), insufficient (20–29 ng/mL), or sufficient (≥30 ng/mL). Clinical and laboratory data, including hemoglobin concentration, annual VOC frequency, genotype, hydroxyurea use, hospitalization frequency, and sun exposure, were collected. Statistical analyses included chi-square tests, independent t-tests, Pearson correlation, and multivariable linear regression. Results: Vitamin D deficiency was identified in 54.0% of participants, whereas only 16.0% demonstrated sufficient vitamin D levels. Mean serum 25(OH)D concentration was 21.23 ± 7.44 ng/mL. HbSS patients exhibited significantly lower vitamin D levels compared with HbAS patients (19.89 ± 6.96 vs. 25.03 ± 7.71 ng/mL, p = 0.031). Serum 25(OH)D levels positively correlated with hemoglobin concentration (r = 0.584, p < 0.001) and inversely correlated with annual VOC frequency (r = −0.692, p < 0.001). Multivariable regression demonstrated that serum vitamin D was independently associated with hemoglobin levels (β = 0.048, p = 0.002) and annual VOC frequency (β = −0.121, p < 0.001) after adjustment for age, sex, genotype, sun exposure, and hydroxyurea use. Sun exposure was significantly associated with vitamin D status (p < 0.001). Conclusions: Vitamin D deficiency is highly prevalent among Sudanese patients with SCD and is significantly associated with anemia severity and increased VOC frequency. Given the single-center design and modest sample size, these findings should be regarded as exploratory and hypothesis-generating. They support routine vitamin D assessment and indicate that targeted supplementation strategies warrant evaluation as potential adjunctive approaches in SCD management in prospective, adequately powered studies.