Serum 25-hydroxyvitamin D is associated with insulin resistance independently of obesity in children ages 5-17.

Aim: To determine the association of vitamin D with insulin resistance and obesity in children.

Methods: A total of 92 obese and 58 non-obese children aged 5-17 years were evaluated. Data were collected related to anthropometric (weight, height), and biochemical parameters (fasting plasma glucose, serum insulin, serum 25-hydroxyvitamin D, lipid profile, vitamin B12, parathormone) and physical examination (blood pressure, acanthosis nigricans, stria, lipomastia). Insulin resistance (IR) was calculated using the homeostasis model assessment (HOMA). HOMA-IR = fasting insulin level (μU/ml) × fasting glucose (mg/dL)/405. A HOMA-IR value >2.5 was defined as insulin resistance.

Results: According to the US Endocrine Society classification, vitamin D deficiency (0-20 ng/ml) was determined at significantly higher rates in the obese group than in the control group (p < 0.001). The rate of subjects with a vitamin D level of 20-30 ng/ml was significantly lower in the obese group than in the control group (p < 0.001) Within the obese group a statistically significant difference was determined between the insulin resistant and non-insulin resistant groups in respect of serum 25-hydroxyvitamin D levels (p = 0.001) and vitamin B12 levels (p = 0.001). A significant negative correlation was determined between serum 25-hydroxyvitamin D and HOMA-IR (r=-0.256, p = 0.016) and insulin (r = -0.258, p = 0.015). The systolic blood pressure (p = 0.001) and diastolic blood pressure (p = 0.003) values were significantly different in the control and obese groups. A statistically significant difference was determined between the control and obese groups in terms of the levels of insulin, HOMA-IR, HbA1c, cortisol, LDL, total cholesterol, HDL, triglyceride, hemoglobin, MCV, MPV, and calcium.

Conclusion: The prevalence of vitamin D deficiency was higher in obese children compared to normal-weight and overweight children. Serum 25(OH)D levels showed a negative correlation with insulin and HOMA-IR. Serum 25(OH)D is associated with insulin resistance independently of obesity.