Deficiency Causes fat malabsorption Presentation ↑ fragility of erythrocytes (hemolytic anemia) muscle weakness neurodysfunction poor joint sensation and ataxia retinitis pigmentosa vitamin A supplementation used as a treatment in retinitis pigmentosa not caused by vitamin A deficiency Excess Presentation synergistic ↓ in vit K dependent clotting factors with warfarin potential hemorrhage in warfarin patients