Transports Fe(2+) from the inside of a cell to the outside of the cell, playing a key role for maintaining systemic iron homeostasis (PubMed:15692071, PubMed:22178646, PubMed:22682227, PubMed:24304836, PubMed:29237594, PubMed:29599243, PubMed:30247984). Transports iron from intestinal, splenic, hepatic cells, macrophages and erythrocytes into the blood to provide iron to other tissues (By similarity). Controls therefore dietary iron uptake, iron recycling by macrophages and erythrocytes, and release of iron stores in hepatocytes (By similarity). When iron is in excess in serum, circulating HAMP/hepcidin levels increase resulting in a degradation of SLC40A1, thus limiting the iron efflux to plasma (PubMed:22682227, PubMed:29237594, PubMed:32814342). {ECO:0000250|UniProtKB:Q9JHI9, ECO:0000269|PubMed:15692071, ECO:0000269|PubMed:22178646, ECO:0000269|PubMed:22682227, ECO:0000269|PubMed:24304836, ECO:0000269|PubMed:29237594, ECO:0000269|PubMed:29599243, ECO:0000269|PubMed:30247984, ECO:0000269|PubMed:32814342}. This is the function of Ensembl gene identifier ENSG00000138449 (SLC40A1, solute carrier family 40 member 1).