Vitamin Distribution in Red Blood Cells, Plasma, and Other Body Fluids

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Abstract
The distribution of vitamins in red blood cells and plasma was determined in seven healthy volunteers. On a volume basis red blood cells were richer than plasma in riboflavin, nicotinate, pantothenate, thiamine, and reduced folates; vitamins A, E, and oxidized pteroylmonoglutamates were undetectable in red blood cells. Vitamins A and E, biotin, B6, B12, and oxidized pteroyltriglutamates together with N5-methyltetrahydrofolate (N5-methyl-THF) were mainly concentrated in plasma as compared with red blood cells; ascorbate was almost equally distributed between red blood cells and plasma. An intravenous multivitamin loading dose produced a large increase of biotin, pantothenate, B6, thiamine, and oxidized pteroyltriglutamates plus N5-methyl-THF in the red blood cell; increases in red blood cell nicotinate, riboflavin, and B12 were minimal. No increase in red blood cell ascorbate, vitamins A and E, and oxidized and reduced pteroylmonoglutamates occured despite their immersion in the vitamin-loaded plasma. Red blood cells seem poorly permeable to these vitamins and such levels are, therefore, not a dependable index of vitamin status at the the blood is drawn. Presumably, most B vitamins and vitamin A quickly concentrate in tissues and other fluids other than the plasma or red blood cells. Folates were the exception; like vitamin E they remained mostly in the plasma. Urinary recovery of intravenous multivitamins varied from undetectable amounts (vitamins A, E, and oxidized pteroyltriglutamates) to 100% (biotin). Only 1.2% of hydroxocobalamin as compared to 19% of cyanocobalamin was recovered in urine indicating a greater body retention of hydroxocobalamin.