FGF23 and acute kidney injury: Lower calcitriol levels in patients with AKI have been attributed to reduced 25-hydroxyvitamin D levels, as well as renal dysfunction due to which less 25-dihydroxyvitamin D substrate is converted to active 1,25-dihydroxyvitamin D. Moreover, increased FGF23 levels could cause reduced activation of 25-hydroxyvitamin D by inhibiting 1 α-hydroxylase and induction of the catabolic 24-hydroxylase, leading to the impaired synthesis of calcitriol from 25-hydroxyvitamin D3 [47].