How an iron supplement is fitted into the day changes how much is absorbed: Moretti 2015 found in young women with low iron stores that a single fasting morning dose of 60 mg or more raises hepcidin, the hormone that closes the gut door to iron, for about 24 hours, and absorption of the next-day dose falls by 35-45%. The authors concluded that alternate-day dosing may be better, though its long-term effects still need study.