Introduction: Vitamin D deficiency is commonly observed in patients with obesity, primarily due to sequestration by adipose tissue. Recent research highlights the importance of this deficiency, showing a correlation between low vitamin D levels and mechanisms contributing to insulin resistance.

Objectives: This study aims to compare the effects of supplementing with 4,000 IU of vitamin D versus 1,000 IU over six months on insulin resistance and the leptin/adiponectin ratio in school-aged children and adolescents with obesity. Materials and

Methods: A controlled clinical trial will be conducted involving 40 children with obesity aged 10 to 18 years (BMI \>95th percentile). Participating children and their parents will undergo measurements such as weight, height, BMI, body fat, and Tanner stage. All participants will receive dietary and physical activity recommendations based on WHO guidelines. After initial assessments, participants will be randomly assigned to receive either 4,000 IU or 1,000 IU of vitamin D. They will be monitored monthly for capsule intake and adverse effects, with follow-up measurements of anthropometry, leptin, adiponectin, insulin \& lipid profile. Statistical Analysis: Baseline characteristics will be compared using t-Student or U-Mann Whitney tests, depending on variable distribution. The intervention's impact will be assessed by calculating deltas for body fat and biochemical measurements, with significance tested using paired t-tests or Wilcoxon tests. Covariance analysis (ANCOVA) will be used to adjust for confounding variables.