Objective: The discovery of vitamin D receptors and vitamin D activating enzymes in several cells other than those involved in bone and mineral metabolism brought the non-classical effects of vitamin D into focus. It was reported that diabetic patients have significantly lower vitamin D concentrations than healthy individuals and vitamin D is a risk factor for diabetes. The high rate of progression to diabetes from prediabetes which is a state where blood glucose levels are higher than normal but not high enough to qualify as diabetes is clinically important. In this study vitamin D levels were investigated in prediabetic patients.

Material and Methods: 24-65 years aged 103 subjects who underwent the Oral Glucose Tolerance Test (OGTT) in Tepecik Training and Research Hospital were included in the study. Fasting blood glucose (FBG), 2nd hour glucose, insulin, HbA1c and 25(OH)D levels of the subjects were measured.

Results: While subjects with impaired fasting glucose (IFG) and combined impaired fasting glucose and impaired glucose tolerance (IGT) have significantly higher vitamin D levels than subjects with normal glucose tolerance (NGT) (p< 0.001, p< 0.001 respectively), there was no significant difference between diabetic patients and subjects with IFG or combined IFG+IGT (p=0.938, p=0.837 respectively). In Pearson correlation analysis vitamin D was significantly negatively correlated with FPG, insulin, HOMAIR( Homeostasis Model Assesment of İnsulin Resistance) and body mass index (BMI) [respectively r=- 0.242 (p=0.014), r=-0.294 (p=0.003), r=-0.296 (p=0.002), r=-0.255 (p=0.009)]. By multiple linear regression analysis vitamin D levels were significantly associated with FPG, insulin and HOMA-IR independently from age, sex and BMI (p=0.040, p=0.020, p=0.022 respectively).

Conclusion: The subjects with prediabetes have significantly lower 25(OH)D concentrations than those with NGT. Additionally, there was a negative relationship between vitamin D and glucose homeostasis parameters independently from age, sex and obesity. Further studies with larger participant groups residing in different regions are required to confirm the relationship of vitamin D to prediabetes and diabetes.