This gives credence to the “two hit” hypothesis, where the combination of increased FGF23 transcription (as a consequence of iron deficiency) in the setting of reduced FGF23 cleavage (as a consequence of the parenteral iron formulation) leads to excess levels of intact FGF23 and the cascade of biochemical abnormalities described above.9–12. Here, FGF23 is linked to nutritional disorder.