PTH and osteoporosis: Later, we have discussed the core mechanisms and pathways involved in the pathophysiology of osteoporosis, including the RANKL-OPG axis, Wnt/β-catenin signalling, Parathyroid hormone (PTH)/PTH1R (cAMP/PKA vs. sustained Ca<sup>2+</sup>/PKC) signalling, TGF-β/BMP-SMAD signalling, etc. Furthermore, we summarise the major risk factors, including ageing, sex hormones, nutritional deficiencies, lifestyle factors, and comorbidities and delineate their mechanistic links to bone loss.