T. J. Clark Liquid 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.