Combination therapy with nutritional vitamin D and calcimimetics in secondary hyperparathyroidism: a mechanism-based approach to restoring PTH regulation.

Secondary hyperparathyroidism (SHPT) in chronic kidney disease (CKD) is commonly interpreted as a compensatory response to disturbances in mineral metabolism, yet this view does not fully account for the biochemical instability and treatment resistance observed in advanced disease. Current therapeutic strategies primarily target individual regulatory pathways. Calcimimetics suppress parathyroid hormone (PTH) secretion through calcium-sensing receptor (CaSR) activation, whereas active vitamin D analogs reduce PTH synthesis via vitamin D receptor (VDR) signaling but are frequently associated with increased mineral load and elevated fibroblast growth factor 23 (FGF-23). Nutritional vitamin D (NVD) restores circulating 25-hydroxyvitamin D [25(OH)D] and supports tissue-level activation of vitamin D pathways without substantial increases in calcium or phosphate. When combined with calcimimetics, NVD provides complementary modulation of PTH regulation through distinct but interacting mechanisms. Experimental and clinical evidence suggests that this combination may enhance responsiveness of parathyroid tissue and contribute to improved biochemical control. At the system level, this approach has been associated with reduced PTH variability, relatively stable calcium balance, stabilization or modest reduction in phosphate, and reduction in FGF-23 compared with active vitamin D-based strategies. However, current evidence remains largely based on surrogate biochemical endpoints. The Evaluation Of Cinacalcet HCl Therapy to Lower Cardiovascular Events (EVOLVE) trial, the largest Randomized Controlled Trial (RCT) of cinacalcet in dialysis patients, demonstrated no significant reduction in the primary composite endpoint of all-cause mortality or major nonfatal cardiovascular events in the intention-to-treat analysis despite consistent biochemical improvements, and the extent to which combination calcimimetic-based therapy translates into improved long-term clinical outcomes therefore remains uncertain.