LAUSR

Abstract Objectives Phosphate is essential for skeletal mineralization, which is regulated by parathyroid hormone, calcitriol and fibroblast growth factor 23 (FGF23). Serum phosphate is physiologically higher in younger children, but factors that contribute to this physiological state are poorly understood. This study aimed to evaluate phosphate and its regulators in children compared with adults. Materials and methods The participants were children aged 3–11 years and adults older than 20 years of age. Biochemical parameters including calcium, phosphorus, alkaline phosphatase, FGF23, and vitamin D were measured. Fractional excretion of phosphate was calculated, using serum and urine phosphate and creatinine. Results This cross-sectional study was conducted on 45 children (mean age: 9.0 ± 2.1) and 44 adults (mean age: 38.9 ± 11.1). The children had higher serum calcium, phosphate, alkaline phosphatase, and FGF23 (p < 0.001), but fractional excretion of phosphate was greater in adults (14.1 ± 5.7, 11.4 ± 4.4, p = 0.019, 95% confidence interval [CI]: −0.7 to −0.2). Of all individuals, 61.8% had vitamin D deficiency. By multiple regression analysis, entering age, calcium, phosphate, and vitamin D level, the only independent predictor of FGF23 was 1, 25 dihydroxy-vitamin D3 (β: 0.78, p < 0.001, 95% CI: 0.5–1.1, R2: 0.59 for children, and β: 0.59, p < 0.001, 95% CI: 0.5–1.4, R2: 0.45 for adults). Conclusion As far as we know, there is little information regarding the role of FGF23 in physiologic state. In this cross-sectional study no association was found between FGF23 and urinary phosphate excretion in growing children. Further studies with more detail are essential to evaluate phosphate homeostasis during childhood.