RBP4 and metabolic syndrome: A relevant number of studies suggested an important link between RBP4 and adiposity (Aeberli et al., 2007; Haider et al., 2007; Jia et al., 2007; Klöting et al., 2007), insulin resistance (Gavi et al., 2007; Klöting et al., 2007; Perseghin et al., 2007; Stefan et al., 2007; Möhlig et al., 2008), type 2 diabetes (Cho et al., 2006; Takebayashi et al., 2007), and the metabolic syndrome (Qi et al., 2007).