Objectives: The objective of this study is to assess the prevalence of vitamin D insufficiency in children with type 1 diabetes mellitus (T1DM) who are receiving care at the Endocrinology outpatient clinic at the Pediatrics Department of Tanta University Hospital. Additionally, the study aims to investigate the impact of vit D supplementation on the progression of T1DM.

Methods: The study was conducted as a prospective randomized and cross-sectional controlled trial at the "Endocrinology Outpatient Clinic" inside the Pediatrics Department of Tanta University Hospital. The research sample was composed of one hundred fifty-two children diagnosed with T1DM. The research methodology used many tools, which encompassed: Medical records are used to collect sociodemographic data. (2) Data associated with the relationship between food consumption and solar radiation exposure. (3). this research focuses on the variables associated with its insufficiency and the levels of vit D investigation. The participants in the research were children who had low vit D levels. These children were then categorized into two separate groups. The intervention group consisted of children who received standard care along with vit D supplementation. The control group consisted of youngsters who received just regular treatment. A further assessment was conducted after six months periods, whereby the previously mentioned examinations were performed for the children in both groups.

Results: Low vit. D levels were found in 78.3% of the studied children. Approximately 29.0% of them had insufficient vit. D level. Mild and moderate vit. D deficiency (VDD) were found among 25.7% and 23.7% of the studied children respectively. After receiving both vit. D and calcium (Ca) supplementations, Levels of vit. D, blood pH, Ca and Magnesium (Mg) increased, while levels of HbA1C, parathyroid hormone (PTH) and alkaline phosphatase (ALP) decreased.

Conclusion: Majority of children with T1DM have low vit. D levels. Bad dietary habits and lifestyles were more observed among children with low vit. D levels. Vit. D and Ca supplementations for at least six months added to the routine insulin dose proved their effectiveness in glycemic control with increased levels of ionized Ca, blood pH and Mg level and decreased levels of PTH and ALP.