At 4 h , serum non-transferrin-bound iron reached peaks with geometric mean ( 95 % CI ) concentrations of 0.81 mol/L ( 0.56 , 1.1 mol/L ) for 60 mg Fe with water and 0.26 mol/L ( 0.15 , 0.38 mol/L ) for 60 mg Fe with food but was at assay limits of detection ( 0.1 mol Fe/L ) for 6 mg Fe with food .