Iron deficiency anemia that does not correct with iron supplementation may indicate a need for riboflavin (vitamin B2), which is crucial for iron absorption.

“the other thing i want to mention about iron and ferritin is there are i've seen many times in people that they have a ferritin deficiency they have an iron deficiency anemia or just frank iron deficiency and it doesn't correct with iron supplementation further down the web you must have riboflavin which is vitamin b2 which we will see again here in a moment in order to absorb iron properly so if you have an iron deficiency anemia that is not correcting with iron supplementation you need riboflavin”