Association of Serum 25(OH)D Levels With Cardiometabolic, Thyroid, and Hematological Risk Factors Among Students of Hormozgan University

Background: Emerging evidence suggests a link between vitamin D deficiency and health conditions; however, regional data from sun-rich areas, such as Hormozgan, remain scarce. Therefore, this study examines the relationship between serum 25-hydroxyvitamin D [25(OH)D] levels and early indicators of cardiometabolic and thyroid dysfunction among students from Hormozgan University. Methods: This cross-sectional study was conducted in 2024 among 223 newly admitted undergraduate students at Hormozgan University in southern Iran. All participants were native residents of Hormozgan Province. Anthropometric data (height, weight, BMI), blood pressure, and fasting venous blood samples were collected. Laboratory assessments included serum 25-hydroxyvitamin D [25(OH)D], thyroid-stimulating hormone (TSH), fasting blood sugar (FBS), and complete blood count (CBC) indices. Linear regression was used to examine associations between serum 25(OH)D levels and clinical indicators. Additionally, a generalized linear model tree (GLMtree) was applied to identify potential subgroups and interaction patterns influencing the relationship between vitamin D levels and health parameters. Results: Out of 223 students, 72% were female. The average age of participants was 19.6 years. Female students had significantly lower 25(OH)D levels (27.13 vs. 32.30 ng/mL, p=0.021) and systolic blood pressure (116.9 mmHg vs. 122.0 in males, p=0.006) compared to males. Vitamin D deficiency was observed in 37% of students, with females representing 79% of this group, and 28% of all students were underweight. Underweight students exhibited higher fasting blood sugar levels (89.96 vs. 86.94 mg/dL, p=0.010). Importantly, 25(OH)D levels showed a positive correlation with fasting blood sugar (β=0.140) and a negative correlation with TSH (β=-0.028) among underweight students, while no significant relationships were found between 25(OH)D and blood pressure or thyroid markers in the overall cohort. Underweight students showed significantly lower average white blood cell counts and mean corpuscular hemoglobin concentration compared to their peers (p=0.014 and p=0.040, respectively. Conclusion: The results showed that vitamin D deficiency is common among students, especially in underweight individuals and girls, and is associated with early changes in thyroid function and glucose metabolism. These findings emphasize the importance of screening and preventive measures to improve vitamin D status and prevent metabolic disorders in the young population.