Effect of Vitamin D Supplementation on Bone Turnover Markers During PrEP in MSM

A total of 50 HIV-uninfected men who have sex with men (MSM) and male to female (M to F) transgender individuals already enrolled in CCTG 595 will be offered participation in the sub-study at Week 24 of the main study. All subjects enrolled into the sub-study will be provided Vitamin D 4000 IU/day supplements in addition to their PrEP at Weeks 24 and 36; clinic visits will proceed normally per main study protocol. Upon completion of the sub-study subjects will continue on the main study. The primary endpoint, bone turnover markers, will be measured from Week 24 to Week 48 via plasma samples collected through the main study. Concurrent controls who are not enrolled in the vitamin D substudy who are reporting supplementation with \< 400 IU of vitamin D/day will be matched 1:1 by randomization arm in the CCTG 595 main study (text messaging arm vs. standard of care), age (± 5 years), race/ethnicity, season of study entry, and BMI (± 3 kg/m2).