Just found this article. It suggests a link between B12 and iron deficiency. I thought it may be interesting. (I had B12 deficiency and iron deficiency at the same time, the iron deficiency corrected itself mysteriously after 2 weeks of B12 loading doses)
Extracted quote to save you reading the whole thing:
"As for the cause of his iron deficiency, gastrointestinal bleeding is a less likely explanation since stool hemoccult test was negative. It is probable that severe intramedullary destruction and hemolysis of erythrocytes from ineffective erythropoiesis result in depletion of iron storage and lead to iron deficiency anemia."