What may cause iron deficiency?!

Bleeding/poor intake: The most common cause is bleeding, which could be "normal" like a woman with periods or abnormal bleeding as in the GI tract. That could be from gastritis, ulcers, abnormal blood vessels, diverticuli (small pockets in the intestines), or tumors (benign or malignant). Also very low iron in the diet (no red meat or green leafy vegetables) or failure to absorb iron from the GI tract can do it.

Iron deficiency: Lack of intake of iron or abnormal loss of iron (through the loss of or leakage of blood) is the way to look at this issue. I.