PTH and metabolic syndrome: In this research, which included a cross-sectional study and another with an interventional design, we investigated Free-25(OH)D and Bio-25(OH)D thresholds based on PTH and three BTMs with adjustment for environmental and genetic confounders, assessed the risk of MetS according to these thresholds, and compared the possible advantages of using Free-25(OH)D and Bio-25(OH)D over Total-25(OH)D.