Suboptimal vitamin D status is well reported in sickle cell disease (SCD) patients and associated with a negative impact on health-related quality of life (HRQL). The investigators enrolled 42 SCD patients and 42 healthy controls, subjects within each group received monthly oral vitamin D3 dose according to the baseline status of vitamin D as follows: sufficient: 100,000 IU, insufficient: 150,000 IU, and deficient: 200,000 IU. The investigators assessed safety and efficacy on normalization of vitamin D level, bone mineral density (BMD), hand grip strength (HGS), and HRQL.

Inclusion Criteria:

• children with SCD (HbSS, hemoglobin sickle beta zero (HbSβ0) thalassemia genotype), aged ≤ 18 years old, male or female study participants who were at a steady state (≥ one month from blood transfusion and ≥ 14 days from any acute sickle complication as hospitalization for Vaso occlusive crisis (VOC) or acute chest syndrome (ACS)), stable Hb level near their usual baseline and stable dose of Hydroxyurea (HÚ) mg/kg for at least 90 days prior to enrollment.
• A control group of 42 healthy age and sex-matching children

Exclusion Criteria:

• SCD patients who are on chronic blood transfusion therapy
• Comorbid chronic conditions
• Use of medications known to interfere with calcium or vitamin D absorption or metabolism
• Known hypercalcemia or vitamin D hypersensitivity
• Use of vitamin D therapy to treat vitamin D deficiency or rickets
• Urolithiasis, liver or renal impairment, and malabsorption disorders.
• Obese children with body mass index (BMI) > 85th percentile for age and sex