Vitamin D in HIV-Infected Patients on HAART

Inclusion Criteria: * HIV-positive men and women age 18 and older. * HIV-1 RNA documented to be \< 200 copies/mL on their current ART regimen, with supporting viral load documentation in the 24 weeks prior to study entry. * Subjects must receive primary HIV care at the UCLA CARE center. * Subjects must be undergoing screening for vitamin D deficiency by their primary care provider at the time of study entry, or have undergone vitamin D screening in the 90 days prior to consent without yet initiating vitamin D supplementation (for insufficient subjects). * Ability and willingness of subject to provide informed consent Exclusion Criteria: * Use of vitamin D supplementation (not including 400 IU daily, the amount in a standard multivitamin) at the time of screening. * HIV-infected subjects not on ART. * HIV-infected subjects not suppressed on their current ART regimen (HIV-1 RNA \> 200 copies/mL in the 6 months prior to screening).