The purpose of this study is to determine the efficacy and safety of vitamin D3 (cholecalciferol) supplementation on HIV progression and incidence of pulmonary tuberculosis among HIV-positive Tanzanian adult men and women initiating highly active antiretroviral therapy (HAART).

HIV-infected adults initiating antiretroviral therapy in resource-limited settings experience high mortality, pulmonary tuberculosis, and other comorbidity rates during the first year of HIV treatment. Observational studies have shown low vitamin D is a risk factor for HIV progression and incidence of pulmonary tuberculosis among adults initiating HAART; however, whether this relationship is causal and if vitamin D supplementation starting at HAART initiation can improve health outcomes has not been determined. This study is a randomized, double-blind, placebo-controlled trial conducted to examine the effect of vitamin D3 supplementation on morality and pulmonary tuberculosis for adults initiating HAART. Participants are HIV-positive Tanzanian men and women aged 18 years and older, who are initiating HAART at the time of randomization whose baseline 25-hydroxyvitamin D (25(OH)D) concentration is \<30ng/mL. Eligible individuals are randomized to receive a) a vitamin D3 regimen consisting 50,000 IU of vitamin D3 taken orally once per week for 4 weeks (weeks 0, 1, 2, 3) followed by 2,000 IU of vitamin D3 supplements taken orally once per day starting at 4 weeks until study discharge at 12 months or b) placebo pills taken once weekly for 4 weeks (weeks 0, 1, 2, 3) followed by placebo pills taken daily starting at 4 weeks until study discharge. Participants will be followed for 12 months after ART initiation.