Here is an article that addresses that very question: 'Vanadium—An Essential Element for Animals and Humans?' Anke M. , Illing-Günther H. , Gürtler H. , Holzinger S. , Jaritz M. , Anke S. , Schäfer U. in Trace Elements in Man and Animals 10, pp 221-225, DOI: 10.1007/0-306-47466-2_58