Staging vitamin B-12 (cobalamin) status in vegetarians.
When one stops eating vitamin B-12 (cobalamins), one passes through four stages of negative cobalamin balance: serum depletion [low holotranscobalamin II, ie, low vitamin B-12 on transcobalamin II (TCII)], cell depletion (decreasing holohaptocorrin and low red cell vitamin B-12 concentrations), biochemical deficiency (slowed DNA synthesis, elevated serum homocysteine and methylmalonate concentrations), and, finally, clinical deficiency (anemia). Serum vitamin B-12 is on two proteins: the circulating vitamin B-12 delivery protein, TCII, and the circulating vitamin B-12 storage protein, haptocorrin. Because TCII is depleted of vitamin B-12 within days after absorption stops, the best screening test for early negative vitamin B-12 balance is a measurement of vitamin B-12 on TCII (holoTCII). HoloTCII falls below the bottom of its normal range long before total serum vitamin B-12 (which is mainly vitamin B-12 on haptocorrin) falls below the bottom of its normal range.
Herbert
V
V
Mount Sinai Medical Center, New York City.
D000042:Absorption; D001921:Brain / Q000378:metabolism; D014676:Diet, Vegetarian / Q000009:adverse effects; D006410:Hematopoiesis; D006801:Humans; D014805:Vitamin B 12 / Q000008:administration & dosage; D014806:Vitamin B 12 Deficiency / Q000175:diagnosis / Q000209:etiology / Q000235:genetics
D014805:Vitamin B 12