Vitamin D Absorption in HIV Infected Young Adults Being Treated With Tenofovir Containing cART

This is a 48 week randomized double-blind, placebo-controlled prospective cohort study of adolescents and young adults with HIV infection in the ATN who are currently being treated with cART that includes TDF as one component of the regimen that includes at least three Food and Drug Administration (FDA)-approved ARVs for at least 180 days. Subjects must have at least one documented viral load that is below 200 copies/mL that is collected following initiation of TDF containing cART and greater than 90 days prior to randomization; no viral load above 200 copies/mL if measured within the 90 days prior to randomization; and an HIV viral load obtained at screening that is below 200 copies/mL. Treatment assignments will be balanced by subject sex at birth, age (\<20 years vs. \>=20 years), and race (African American vs. other). Enrolled subjects will be randomized to receive vitamin D3 50000 IU or matching placebo, given orally every four weeks by DOT. In addition to the randomized study agent, all subjects will receive a MVI to be taken orally once daily. This "standard" MVI will contain ingredients not to exceed 600 IU of vitamin D3 and 200 mg Ca. Dual energy x-ray absorptiometry (DXA) measurement of bone mineral content (BMC)/bone mineral density (BMD) of whole body, spine, and hip, will be performed at baseline and study weeks 24 and 48. Blood and urine sampling to assess the Ca-phosphorous (PO4) axis, parathyroid hormone (PTH)-FGF23-vitamin D signaling, bone turnover, and renal glomerular and tubular function will occur at baseline and study weeks 12, 24, and 48. Blood samples to measure Gluc homeostasis will be drawn at baseline and week 48, and will be run by batch analysis. Safety, measured by serum calcium (SCa) and serum creatinine (SCr), will be monitored by subject's record review at study sites since these labs will generally be measured as a part of routine clinical care. The Adolescent Medicine Trials Network for HIV/AIDS Interventions 109 (ATN 109) study will use the SCa and SCr values obtained within 10 weeks at the time of the visit beginning at the baseline visit. If these evaluations were not performed within the prior 10 weeks they will be drawn at the time of each visit. Viral load and cluster of differentiation 4 (CD4) cell count results will be recorded for this study, ATN 109, at screening, baseline and study weeks 12, 24, 48, and Post-Week 48 provided the evaluations were done within the protocol specified timeframe. If the evaluations were not performed within the protocol specified timeframes they will be drawn at the time of the visit.