FGF23 and metabolic syndrome: Several previous studies have reported that markers of the metabolic syndrome such as body fat accumulation, the blood glucose level, and insulin resistance show both a negative correlation with the plasma phosphate level and a positive correlation with the concentration of PTH or FGF23.(10,19,33) Therefore, we examined the possibility that phosphate, PTH, or FGF23 exert direct effects on adipose tissue or the liver through in vitro experiments using 3T3-L1 and HepG2 cells.