Low iron levels occur when the body needs increased iron, such as during pregnancy, during periods of fast growth and after blood loss, according to the Centers for Disease Control and Prevention. Another cause is a decreased iron intake caused by poor iron absorption or a lack of dietary iron.
Infants and toddlers sometimes become low on iron due to the rapid growth during that period, notes the CDC. Pregnant women also need more iron than normal due to increased blood production for their own bodies and their babies, states Mayo Clinic.
Certain diets, such as a vegetarian diet, tend to be lower in iron, explains the CDC. Other people have difficulty absorbing iron even when they eat iron-rich foods. Problems with the intestines or taking certain medications, such as antacids, can affect how much iron the body absorbs.