Vitamin D Supplementation and Glycemic Control in Patients with Type 2 Diabetes

Abstract

Purpose: Treatment guidelines for the management of patients with type 2 diabetes (T2DM) and vitamin D deficiency do not exist. The primary purpose of this project was to describe repletion rates, prescribing patterns and monitoring patterns for patients with T2DM and vitamin D deficiency. This is a first step in the development of management guidelines. A secondary purpose was to examine glycemic control before and after correction of vitamin D hypovitaminosis. This was done in order to determine if future interventional studies examining the efficacy of treating vitamin D deficiency for patients with T2DM are warranted. Significance: In the United States 25.8 million (8.3%) individuals have diabetes; 90 to 95% have T2DM. The disease is responsible for increased morbidity and mortality as well as annual costs in the billions. Vitamin D deficiency in the United States is estimated to affect 70% of Caucasians and 95% of African Americans. A link between T2DM and vitamin D deficiency has been described. However, guidelines for vitamin D repletion of individuals with T2DM are not available, and the effect of vitamin D repletion on glycemic control has not been well studied. Methods: This project was a non-experimental retrospective audit of electronic medical records used in the outpatient diabetes department of a University Medical Center. Data were collected from the Epic documentation system. Descriptive statistics were used to describe care processes, and a paired samples Student t-test was used to examine A1C levels before and five to eight months after vitamin D repletion for subjects successfully repleted. Results: A total of 366 subjects qualified for inclusion in the study. Follow-up testing ranged from one to twelve tests per subject with a mean of 2.6 (SD = 1.5) and a range from 0 to 12 tests. Successful repletion rates per follow-up period ranged from 4.7 to 23.6%. Five to eight months after initiation of vitamin D, only 97 subjects (26.5%) were successfully repleted. Within this group results demonstrated a significant decrease from an initial to a follow-up mean A1C value (8.33 ± 0.69 vs 7.9 ± 1.3), indicating improved glycemic control (t = 3.58, p = .001). Conclusions: Treatment guidelines and standardization of care for patients with T2DM and vitamin D deficiency are needed. Further investigation is needed to investigate why the majority of patients were not successfully repleted. The findings of improved glycemic control for subjects with repletion also indicate a need for interventional studies with randomized controlled trials to investigate the effect of treating vitamin D deficiency on glycemic control.