Vitamin D Status and Glycemic Control: Experience of the Biochemistry Laboratory, Mohammed VI University Hospital, Oujda, Morocco

Abstract

Background Vitamin D is best known for its role in calcium and phosphate homeostasis, but it may also influence metabolic function. It has been suggested that vitamin D may be linked to glucose regulation. Accordingly, vitamin D status has attracted considerable interest as a potential determinant of glycemic control in diabetes. Although multiple studies have suggested that lower serum 25(OH)D concentrations are associated with higher HbA1c, the overall evidence remains mixed. Objective This study aimed to evaluate the association between serum 25(OH)D and glycated hemoglobin (HbA1c) among hospitalized diabetic patients at Mohammed VI University Hospital, a tertiary care hospital in Oujda, Morocco, and to assess whether hypovitaminosis D is linked to uncontrolled diabetes. Methods We conducted a retrospective, cross-sectional study in the Biochemistry Department over a 12-month period. Hospitalized patients with known type 1 diabetes (T1D) or type 2 diabetes (T2D) who had 25(OH)D and HbA1c measured during the same admission were included; only the first paired measurements were retained. Patients with missing data or conditions likely to bias vitamin D or HbA1c interpretation were excluded. Serum 25(OH)D and HbA1c were measured using routine laboratory methods. Vitamin D status was categorized as <10 ng/mL, 10-30 ng/mL, and >30 ng/mL. Glycemic control was defined as controlled versus uncontrolled using a prespecified HbA1c threshold. Results A total of 100 patients were included (45 men, 55 women; mean age 53 years; range 8-85), including 79 with T2D and 21 with T1D. The mean 25(OH)D was 20.84 ± 11.56 ng/mL, and the mean HbA1c was 7.15 ± 1.64%. The mean HbA1c decreased stepwise across vitamin D categories (8.90%, 7.01%, and 6.36%, respectively). The prevalence of uncontrolled diabetes was 80.0% (12/15) in the <10 ng/mL group, 34.9% (22/63) in the 10-30 ng/mL group, and 4.5% (1/22) in the >30 ng/mL group (p < 0.05). Serum vitamin D was inversely associated with HbA1c in continuous analysis (p < 0.05). When dichotomized, uncontrolled diabetes was more frequent with low vitamin D (≤30 ng/mL) than with normal vitamin D (>30 ng/mL) (43.6% vs. 4.5%; p < 0.05). Conclusion In this hospitalized diabetic cohort, lower serum 25(OH)D levels were significantly associated with higher HbA1c and a markedly greater prevalence of uncontrolled diabetes. While causality cannot be inferred from this retrospective design, hypovitaminosis D may identify patients at higher risk of glycemic disequilibrium, and further studies are needed to clarify clinical implications after accounting for key confounders.