Vitamin A levels and posttransplant intestinal permeability, acute GVHD (AGVHD), GI GVHD, and treatment-related mortality (TRM). Vitamin A levels were normally distributed at 30 days posttransplant. Levels below the median were associated with significantly higher rates of acute GVHD (and specifically mild as well as severe acute GI GVHD) and TRM. Additional data in the article showed that lower vitamin A levels were associated with threefold higher rates of “mucosal barrier injury” blood stream infections (a surrogate marker for increased intestinal permeability) and increased CCR9 expression on effector memory T cells which promotes increased intestinal lymphocyte homing. For all variables shown, the converse was otherwise true for patients whose vitamin A levels were equal to or greater than the median. The 1 exception was that low levels of intestinal fatty acid–binding protein were not impacted by vitamin A status. *Cumulative incidence through day 100 posttransplant.