FGF23 and chronic kidney disease: The effect of activated vitamin D on FGF23 was also significantly higher in comparison to the four studies in patients with CKD stages 2–4, who received native vitamin D (+72 pg/ml [95% CI: 19–126 pg/ml] vs. +5 pg/ml [95% CI: −6 to 15 pg/ml] P = 0.01).