Fibroblast growth factor 23 (FGF23) is a hormone that plays a critical role in regulating mineral homeostasis in the body. Specifically, FGF23 acts on the kidneys to decrease the reabsorption of phosphate from the blood and into the urine. This process helps to reduce serum phosphate levels and maintain balance alongside other hormones such as PTH. The primary responsibility of FGF23 is to regulate the balance of phosphate in the body. It does this by acting on the kidney cells to decrease the reabsorption of phosphate from the blood and into the urine. This process allows the body to excrete excess phosphate to maintain normal serum phosphate levels in the blood. In addition to regulating phosphate levels, FGF23 also plays a role in the metabolism of vitamin D. FGF23 can increase the metabolism of vitamin D to an inactive form, reducing the amount of active vitamin D in the body. This reduction in active vitamin D levels leads to decreased intestinal absorption of dietary calcium and phosphate. Abnormal levels of FGF23 in the body have been associated with several health concerns, particularly in patients with chronic kidney disease. High levels of FGF23 have been linked to the development of bone loss, vascular calcification, and cardiovascular disease. Conversely, low levels of FGF23 have been associated with an increased risk of mortality and cardiovascular disease in patients with kidney disease.