### Background and Objective

Type 1 diabetes (T1D) is a chronic metabolic disorder characterized by impaired insulin secretion and is associated with adverse alterations in body composition, including increased fat mass and reduced fat-free mass, as well as disturbances in the lipid profile, such as elevated triglyceride and cholesterol levels. These metabolic alterations may increase the risk of cardiovascular complications. In children and adolescents with T1D, maintaining favorable body composition and lipid concentrations is therefore an important component of long-term disease management and cardiovascular risk reduction, alongside appropriate glycemic control. Regular physical activity may also contribute to improved metabolic regulation and healthier body composition in this population. The present study aimed to investigate the effects of vitamin D supplementation combined with aerobic exercise on body composition and lipid profile indices in children with type 1 diabetes.

### Materials and Methods

In this randomized controlled clinical trial, 48 children with type 1 diabetes, aged 9–11 years, residing in Kermanshah, Iran, were enrolled. Participants were randomly assigned to four groups (n=12 per group): vitamin D plus aerobic exercise (VitD+T), vitamin D alone (VitD), aerobic exercise plus placebo (P+T), and placebo (P). Participants in the vitamin D groups received one 1,000-IU vitamin D capsule daily for eight weeks. Participants in the exercise groups performed moderate-intensity aerobic exercise three sessions per week for eight weeks. Body composition and lipid profile indices were assessed in all participants before and after the intervention using standardized methods and instruments. Data were analyzed using IBM SPSS Statistics version 22, with statistical significance set at P<0.05.

### Results

Regarding the lipid profile, only LDL cholesterol showed a statistically significant change. The VitD+T group demonstrated a greater reduction in LDL cholesterol compared with the other groups, and the between-group difference was statistically significant (P=0.003). No significant between-group differences were observed in total cholesterol, triglycerides, or HDL cholesterol. Regarding body composition, only body fat percentage showed statistically significant changes. The VitD+T and P+T groups demonstrated significant improvements in body fat percentage compared with the other groups.

### Conclusion

Overall, the findings suggest that combining moderate-intensity aerobic exercise with daily vitamin D supplementation may lead to relative improvements in selected lipid profile and body composition indices in children with type 1 diabetes and vitamin D deficiency. The combined intervention was associated with a greater reduction in LDL cholesterol and improvements in body fat percentage than the other intervention conditions. These findings suggest that integrating vitamin D supplementation with regular moderate-intensity aerobic exercise may represent a potentially beneficial complementary approach for supporting metabolic health in children with T1D and vitamin D deficiency. Further studies with larger samples, longer intervention periods, and comprehensive assessment of dietary intake, insulin dosage, and physical fitness are warranted to confirm these findings.