Compared with participants who did not receive iron supplementation , those who received iron supplementation had shortened time to 80 % hemoglobin recovery in both the low-ferritin ( mean , 32 days , interquartile range [ IQR ] , 30-34 , vs 158 days , IQR , 126 - > 168 ) and higher-ferritin groups ( 31 days , IQR , 29-33 , vs 78 days , IQR , 66-95 ) .