FGF23 and Hypertension: Secondary analysis of the placebo-controlled Styrian Vitamin D Hypertension trial (186) trial in 181 adults with arterial hypertension and a low serum concentration of 25(OH)D (<30 ng/mL) has indicated that while vitamin D supplementation (2,800 IU daily) had no effect on FGF23 levels in the overall cohort, it did have an effect in subgroups with a baseline below 20 nl/L.