Vanadium

Abstract

Vanadium is a transition element (atomic weight 50.94) with valences -1, 2, 3, 4, and 5. The most common biological forms are the pentavalent vanadate anion (VO3-) and the quadrivalent vanadyl cation(VO2+). Minimal amounts of vanadium appear to be needed for human health, but a specific essential function has not yet been found. The foods containing the largest amounts of vanadium per serving include shellfish, herbs (parsley, dill weed), and mushrooms. It is not known what the consequences of vanadium deficiency in humans are, since requirements are always covered. Canning and other forms of processing increase the content in low-vanadium foods. Undesirable effects of very high oral doses (> 10 mg/day) include gastrointestinal discomfort and green coloring of the tongue. Slowed growth, renal failure, and respiratory and cardiovascular distress might occur at very high doses. Only a small percentage (possibly 1–5%) of ingested vanadium is absorbed. Vanadate appears to be 3–5 times more bioavailable than the vanadyl form. Since vanadylate is reduced in the stomach to vanadate, the efficiency of uptake can be expected to depend both on stomach conditions and residence time of an ingested dose. Vanadylate is known to bind to transferrin and ferritin, possibly also to other iron-binding proteins, which raises the possibility that vanadium uptake proceeds at least partially via the non-heme iron absorption pathways. Most ingested vanadium appears to be excreted with urine and neither the forms excreted nor the mechanisms underlying excretion have been elucidated.