Those most vulnerable to iron deficiency are infants, adolescents, pregnant or lactating women, vegetarians, people on diets, premenopausal women, and people with bleeding problems. People taking certain drugs, such as allopurinol for gout, tetracyclines, or high amounts of aspirin, may have impaired absorption of iron and thus may develop iron deficiency over time.

Both iron deficiency anemia and iron deficiency without anemia occur fairly commonly when a rapid growth period increases iron needs which are often not met with additional dietary intake. Several studies have shown that often more than half of children aged 1-5, teenagers, and women aged 18-44 had iron intakes below the RDA.

Females need more iron than men but often consume less. Iron deficiency is particularly common in pregnancy, especially later pregnancy, when the fetus needs about 7-8 mg. per day. Even though there is better absorption at this time than the average 10-20 percent of intake, the average diet supplies only 15-25 mg. per day, which is not enough to meet the needs of both mother and child.

Iron deficiency anemia is characterized as microcytic (the RBCs are small) and hypochromic (the RBCs are pale because of decreased hemoglobin). This type of anemia can be determined by doing a complete blood count and checking the hemoglobin, hematocrit, and red blood cell count, along with the RBC indices-the MCV (mean corpuscular volume), MCH (mean corpuscular hemoglobin), and MCHC (mean corpuscular hemoglobin concentration). The doctor or lab technician can also easily see small, pale red blood cells under the microscope. Iron deficiency can occur and generate vague symptoms before clinical anemia actually occurs. This state may be assessed by checking the serum iron concentration. If this is low, it may suggest iron deficiency, usually from low intake or increased losses. Even before serum iron is low, iron saturation, serum transferrin (iron-carrying protein), total iron binding capacity (TIBC), or, more recently, the ferritin level may be measured to detect low iron stores. The body will draw on these muscle and tissue stores to maintain normal serum levels.

Anemia is basically defined as a reduction in the number of red blood cells. Other factors besides iron, such as low copper, manganese, zinc, pyridoxine (vitamin B6), folic acid, and vitamin B12 may also affect the RBCs. Vitamin B6 and zinc deficiency may mimic iron deficiency, but giving iron may lead to iron toxicity problems in these cases. Measuring serum iron is the best way to ensure that the problem is actually iron deficiency, and measuring B6 and zinc levels can help diagnose those hidden, though common, deficiency problems as well. So iron deficiency is but one cause of anemia. I have discussed the B12 and folic acid vitamin deficiency anemias in Chapter 5, Vitamins; copper, zinc, and manganese are some minerals whose deficiency can cause other forms of anemia. Thyroid problems or lead toxicity may cause anemia as well. We also need adequate protein, calcium, and vitamins E and C to keep our red blood cells healthy. Thus, many nutritionally related problems can lead to anemia; decreased production or increased destruction of RBCs and bleeding, however, are the most common causes. Overall, it is wise to diagnose and treat the definitive cause of anemia, not just give iron.

Many symptoms may arise from iron deficiency. Fatigue and lack of stamina usually arise first, caused by fewer red blood cells, low hemoglobin, and a reduced ability to hold and carry oxygen. Children who are iron deficient may experience psychological problems, learning disabilities based on hyperactivity or a decreased attention span, and even a lower IQ, besides other symptoms of anemia. Headaches, dizziness, weight loss from decreased appetite, constipation, and lowered immunity (a weakened resistance) may occur. With anemia, paleness of the skin, cheeks, lips, and tongue may occur, as can a sore tongue, canker sores in the mouth, hair loss, itching, and brittle nails. Not uncommon is a general state of apathy, irritability, and/or depression—a lack of enthusiasm for life—which can, however, improve rapidly with iron supplementation. Decreased memory may also occur. In children particularly, iron deficiency may cause a strange symptom called "pica"—eating and sucking on inedible objects, such as toys, clay, or ice. This usually disappears with iron treatment. In pregnancy, morning sickness may occur more frequently with low iron, perhaps because of the relatively low oxygen distribution to cells. It can take several months for improved absorption and increased intake to catch up to needs.