Bone is a metabolically active tissue undergoing continuous remodeling through the coordinated actions of osteoclasts (resorption), osteoblasts (formation), and osteocytes (regulation). Under physiological conditions, bone formation and resorption are balanced and regulated by systemic hormones (PTH, vitamin D, estrogens) and local mediators. However, aging, metabolic disorders, physical inactivity, or pharmacological treatments may disrupt this equilibrium, leading to the predominance of one process over the other. Circulating biochemical markers of bone turnover-classified into formation markers (P1NP, osteocalcin, bone alkaline phosphatase) and resorption markers (CTx-I, NTx-I, DPD)-provide a means to monitor these dynamics.
Beyond its mechanical role, bone also functions as an endocrine organ: osteocalcin, secreted by osteoblasts, modulates insulin secretion and sensitivity, linking bone to muscle and adipose tissue in the regulation of energy metabolism. Adipokines such as leptin and adiponectin further contribute to this complex crosstalk. Bone biomarkers are therefore essential for evaluating skeletal metabolism and identifying conditions such as osteoporosis, though the strict classification into formation versus resorption markers is limited, as some (e.g., osteocalcin) reflect both processes.
This study aims to analyze IRCCS San Raffaele database records of urinary and serum biomarkers related to bone, muscle, and energy metabolism, to assess their trends and associations according to age and sex, and to develop statistical models capable of explaining their interrelationships.