FGF23 and chronic kidney disease: One previous cohort study with 2,496 participants aged 70–79 analyzed the relationship between Klotho and incident CKD, as well as the interaction between Klotho and FGF-23 or phosphorus, demonstrating the association between low serum Klotho levels and the decline in kidney function, while another study demonstrated a different result that Klotho levels increased in patients with worse kidney function (13, 14).