Background: Various studies have been reported on the relationship between vitamin D, whose deficiency has been identified in a pandemic way, and metabolic-endocrine diseases, including insulin resistance. Insulin resistance is an important public health issue since it is a common cause of death as it transforms into metabolic syndrome and type 2 diabetes mellitus (DM). In this study, the aim is to investigate the relationship between the level of serum 25 hydroxy vitamin D (25(OH)D) and insulin resistance.
Methods: A retrospective study was carried out including 2,008 patients aged between 18 - 67 chosen from among the patients who had applied to Saglik Bilimleri University Antalya Training and Research Hospital. Patients were divided into three groups as non-diabetic, pre-diabetic, and diabetic according to their blood glucose profile and into three categories according to their 25(OH)D levels. The relationship between serum vitamin D levels and insulin resistance was compared between the groups. Individuals with homeostasis model assessment of insulin re-sistance (HOMA-IR) > 2.5 were considered to have insulin resistance.
Results: The study was composed of 2,008 patients, 1,614 were female (80.4%). Of the participants, 216 (10.6%) were diabetics, 849 (42.3%) were pre-diabetics, and 943 (47.1%) were non-diabetics. It was identified that age, fasting blood glucose, HbA1c, triglyceride (Tg), very-low-density lipoprotein cholesterol (VLDL-C), fasting insulin, and HOMA-IR levels were significantly higher in diabetic patients than in pre-diabetic patients (all p < 0.001) and similarly higher in pre-diabetics than in non-diabetics. Tg, VLDL, fasting insulin, and HOMA-IR levels were significantly lower in the group with 25(OH)D ≥ 30 ng/mL. Especially in pre-diabetic individuals, a significant negative correlation was observed between the 25(OH)D level and HbA1c (p = 0.020), Tg (p = 0.001), VLDL-C (p = 0.001), fasting insulin (p < 0.001) and HOMA-IR (p < 0.001). While high HOMA-IR was positively associated with fasting blood glucose and total cholesterol values (all p < 0.001), it was negatively associated with age (p < 0.001), LDL-cholesterol (p < 0.001), HDL-cholesterol (p < 0.001) and 25(OH)D (p = 0.001).
Conclusions: Diabetic subjects have lower plasma 25(OH)D levels and pre-diabetics with hypovitaminosis D have higher risk for insulin resistance. Thus, HOMA-IR must be well evaluated in pre-diabetic individuals with vitamin D deficiency/insufficiency, if there is associating abdominal obesity.