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VANADIUM
Vanadium (V), atomic number 23, is a trace element that is present at low
levels 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. |
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