Children and adolescents with psychiatric illnesses who are treated with medications called second generation antipsychotic agents (SGA) often gain excessive weight during their treatment with these medications. This weight gain may result in the development of features of the metabolic syndrome or frank diabetes mellitus. There is no consensus on the best way to prevent these complications. The investigators' hypothesis is that daily vitamin D supplementation in these patients will result in decreased levels of the markers of metabolic syndrome with associated reduction in waist circumference.

In this 8-week open label trial, we will enroll 10 subjects who fulfill the Inclusion Criteria.

Inclusion Criteria:

1. Males/females between the ages 10 through 18 years,
2. Subjects with Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition (DSM-IV)[62] Axis 1 diagnosis who are on treatment with SGA. These conditions include schizophrenia, schizo-affective disorder, and psychosis,
3. Subjects who have gained 10% of their pre-drug body weight while receiving the following SGAs: risperidone, aripiprazole, clozapine, quetiapine and olanzapine. Subjects could be taking other psychotropic agents, but only one SGA,
4. All subjects will be able to take the prescribed vitamin D by mouth,
5. All subjects will have a 25-hydroxyvitamin D level of < 32 ng/mL,
6. All subjects must reside in an in-patient psychiatric facility.

Exclusion Criteria:

1. Pregnant or lactating women,
2. Patients with mental retardation (intelligence quotient < 50),
3. Subjects with specific systemic diseases such as diabetes mellitus, liver and kidney diseases,
4. Subjects with known history of parathyroid disorder,
5. Subjects with acquired or congenital disorders of vitamin D metabolism,
6. Subjects on calcium and vitamin D replacement therapy, such as calcium carbonate, or ergocalciferol, or cholecalciferol,
7. Subjects taking any weight loss medications, such as orlistat, and sibutramine,
8. Subjects on medications that might affect glucose levels, such as insulin or metformin.