Iron deficiency, the most common cause of anemia, is prevalent in 10 percent to 30 percent of the world's population. Inadequate intake of iron may be an important causative factor, particularly when the body requires more iron than usual (e.g., during infancy, early childhood, adolescence, pregnancy and periods of blood loss). The popular increase of fiber in diets may increase the incidence of iron-deficiency anemia because too much fiber in the diet renders available iron unabsorbable. Symptoms in children include skin or conjunctival pallor, excessive sleepiness, learning disabilities, diminished attention span, tiredness, irritability or inappropriate behavior, and pica. Adults may have shortness of breath, decrease in exercise tolerance, palpitations, tachycardia, angina, congestive heart failure, orthopnea and edema. Iron deficiency occurs in sequential states and is measured by many laboratory tests. The levels of hemoglobin and hematocrit are both decreased, while the red blood cell count may be normal initially, but will decrease as the iron-deficiency state continues. The steps of treatment include correction of the underlying disorder, administration of the amount of iron needed and observation of the response to treatment.