Prevalence of Vitamin D Deficiency and Its Association With Anemia Severity in Anemic Patients: A Cross-Sectional Study.

Background Vitamin D deficiency remains highly prevalent in India, even though the population is exposed to abundant sunlight throughout most of the year. However, data evaluating vitamin D status specifically among anemic adult populations in routine clinical settings remain limited. This study was undertaken to determine the prevalence of vitamin D deficiency in patients with anemia and to examine its relationship with hemoglobin concentration, the severity of anemia, and the underlying anemia subtype. Methods This cross-sectional, hospital-based observational study was conducted over six months in the department of general medicine at a tertiary care center in South India. A total of 246 anemic patients (hemoglobin <11 g/dL) aged >13 years were enrolled after obtaining informed consent. Demographic data, body mass index (BMI), sun exposure duration, skin type, and dietary vitamin D intake were recorded. Laboratory evaluation comprised measurement of hemoglobin concentration, serum ferritin, total iron-binding capacity (TIBC), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and serum 25-hydroxyvitamin D levels. Vitamin D status was defined based on serum 25-hydroxyvitamin D concentrations and categorized as deficient (<20 ng/mL), insufficient (20-29 ng/mL), or sufficient (≥30 ng/mL). Anemia was subsequently categorized according to both severity and etiological type. Results The mean age of the patients was 45.31 ± 18.27 years, with females constituting 156 participants (63.4%). The mean hemoglobin concentration was 8.68 ± 1.81 g/dL. Based on severity, moderate anemia was most common, observed in 121 patients (49.2%), followed by mild anemia in 87 (35.4%) and severe anemia in 38 (15.4%). Iron deficiency anemia was the predominant anemia type, identified in 165 patients (67.1%), while anemia of chronic disease and megaloblastic anemia were present in 71 (28.9%) and 10 patients (4.1%), respectively. The mean serum 25-hydroxyvitamin D level was 23.71 ± 12.00 ng/mL. Vitamin D deficiency was noted in 100 patients (40.7%) and insufficiency in 76 patients (30.9%), resulting in an overall prevalence of suboptimal vitamin D status in 176 patients (71.6%). Mean hemoglobin levels differed significantly across vitamin D status categories (ANOVA, p = 0.017) and dietary vitamin D intake categories (ANOVA, p = 0.008). Analysis revealed a statistically significant association between vitamin D status and the severity of anemia (χ² = 16.01, p = 0.003). In contrast, vitamin D status showed no significant relationship with the etiological classification of anemia (p = 0.531). Similarly, dietary vitamin D intake was not significantly associated with either anemia severity or anemia type. Pearson's correlation analysis indicated the absence of a meaningful linear relationship between serum vitamin D concentrations and hemoglobin levels (r = 0.050, p = 0.434). Conclusion Vitamin D deficiency is highly prevalent among anemic patients. Although serum vitamin D levels did not show a significant linear correlation with hemoglobin concentration, categorical vitamin D status was associated with anemia severity in a non-linear manner, highlighting the potential clinical relevance of vitamin D status in anemic populations.