What is retinol binding protein 4 (RBP4)?

Retinol binding protein 4 (RBP4) is a carrier protein that transports retinol (preformed vitamin A) in the blood from the liver to other tissues.^[1] Single-nucleotide polymorphisms (variants) in the gene that codes for the RBP4 protein appear to be associated with retinol concentrations in the blood^[2] and the risk of some conditions, including childhood obesity,^[3] coronary artery disease,^[4] insulin resistance,^[5] gestational diabetes,^[6] and type 2 diabetes.^[7][8][9] The concentration of RBP4 protein in the blood has also been shown to be associated with the risk of gestational diabetes and type 2 diabetes.^{[10][11][12][13]} However, while experiments using genetic mouse models support some of these associations,^[1][14] further clinical studies are needed to fully understand whether RBP4 plays a causal role in human disease.