The investigators' preliminary data suggest that low levels of vitamin A directly impact risk of mucosal barrier injury laboratory-confirmed bloodstream infection (MBI-LCBI) and they believe supplemental vitamin A at the time of hematopoietic stem cell transplantation (HSCT) can reduce the risk of MBI-LCBI and gastrointestinal graft versus host disease (GI GVHD). In addition, the investigators' preliminary data suggest that a significant number of patients requiring HSCT have vitamin D deficiency even prior to transplantation, and that persistent and newly developed deficiency post-HSCT resulted in worse outcomes.