Objective: To investigate the interaction effects of vitamin D supplementation and aerobic exercises on balance control and physical performance in children with Down syndrome (DS).

Methods: Forty-five children with DS ranging in age from 8 to 12 years will be selected and will participate in this study. They will be assigned randomly using sealed envelopes into three equal groups (A, B and C). Group A will consist of 15 children and will receive the conventional physical therapy program (CPTP) only. Group B will consist of 15 children and will receive the CPTP plus the aerobic exercises. Group C also will consist of 15 children and will receive the CPTP, the aerobic exercises and Vitamin D supplementation in the form of an oral dose of vitamin D3 1000 IU (Cholecalciferol). The program of treatment will be 3 days/week for 12 weeks. Evaluation of balance by using the biodex balance system and physical performance by using the six-minute walk test (6MWT) will be conducted at baseline and after 12 weeks of the treatment program.

Inclusion Criteria:

• Children with DS who can stand and walk independently
• Children with 25 (OH) vitamin D levels of 16 ng/ml or less
• Children who are not consuming estrogens, steroids or other medications that could interfere with vitamin D metabolism
• The absence of visual and hearing impairments that could interfere with testing and training protocols
• Children with mild intellectual disabilities and were capable of understanding visual and verbal instructions.

Exclusion Criteria:

• Medical conditions that will severely limit a child's participation in the study as cardiac problems.
• Musculoskeletal deformities of the lower limbs.

The outcomes assessor will be blinded to which each child allocated to any one of the three arms.