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VANADIUM
Vanadium (V), atomic number 23, is a trace element that is present at
low levels (nanograms per gram or less) in most plant and animal tissues.
The highest concentrations of vanadium in mammalian tissues are in kidney,
spleen, liver, bone, testes and lung. The total human body content is
believed to be between 0.1 and 1 mg. No specific biochemical function has
been identified for vanadium in higher animals. In lower forms of life,
vanadium is a component of several bromo- and iodo-peroxidases. In vitro
vanadium has regulatory effects on numerous enzymes, including protein
tyrosine phosphatases and kinases, and mimics insulin to a substantial
degree. In vivo it may be needed for normal iodine metabolism and/or
thyroid function. Vanadium at pharmacological (i.e., non-nutritional)
levels is known to have hypoglycemic and hypolipidemic effects.
Deficiencies: Deficiencies of
vanadium are unknown in humans. In rats, chicks and goats, a variety
of inconsistent deficiency symptoms have been seen but only under
conditions of synthetic diets with all vanadium excluded. Signs include
reduced growth, poor bone development, impaired reproductive capacity and,
in chicks, poor feather development.
Diet recommendations: The Estimated Safe and Adequate
Daily Dietary Intake is about 100 µg/day. No clear role of vanadium has
been established in humans. Bioavailability is very low, usually found to
be less than 1% of an administered dose. Thus, most ingested vanadium is
excreted unabsorbed. The best food sources include parsley, black pepper,
dill, mushrooms and shellfish. Fresh fruits, legumes and dairy products
usually contain very low levels of vanadium; however, processing (e.g., to
produce dried milk powder or canned apple juice) increases vanadium
levels.
Clinical uses: Both vanadyl sulfate and sodium
metavanadate are being tested as anti-diabetic agents in clinical trials;
however, there are as yet no vanadium compounds in routine clinical use.
Vanadium is sometimes used informally by body builders; however, this
practice is without scientific backing or verifiable evidence of a
positive effect.
Toxicity: Vanadium is generally more toxic when
inhaled than when taken orally. Toxic levels vary considerably, depending
on the age and species of animals, and on other components of the diet
such as protein content and other trace elements. Humans have taken quite
large doses (up to 25 mg vanadium/day for adult males) in experimental
settings for up to 5 months. There were only minor complaints (green
tongue, GI upset) at the higher doses. In experimental animals toxicity
symptoms include dehydration, weight loss, depressed growth, diarrhea,
breathing difficulties, cardiac irregularities and loss of renal function.
The LD50 for rats has been determined as
0.8 mmol/kg (approximately 50 mg as sodium metavanadate),
Recent research: The relationship between
vanadium intake and thyroid metabolism and the glucose-lowering effect
of orally administered vanadium are two topics of current research
interest. |
