Demographics
The exact number of people in any country with anemia is difficult to determine because the disorder often goes undiagnosed. According to the National Heart, Lung, and Blood Institute (NHLBI), anemia affects more than 3 million Americans. Other sources estimate that 4% of men and 8% of women in the general populations of Canada, the United States, and Western Europe have mild anemia. It is thought that the rates of anemia are 2-5 times higher in the developing countries. According to the World Health Organization (WHO), iron deficiency is the most important nutritional disorder in the world. WHO, estimates that 80% of the world's population may be iron deficient. The prevalence of vitamin B12 deficiency among the geriatric population is estimated at 5-15%. Although the prevalence of anemia is greater in women than men aged less than 75, by age 75, male prevalence surpasses female prevalence by about 5%. Anemia can be mild, moderate, or severe enough to lead to life-threatening complications. More than 400 different types of anemia have been identified, many of which are rare.

Iron deficiency anemia
The onset of iron deficiency anemia is gradual and, at first, there may not be any symptoms. The deficiency begins when the body loses more iron than it derives from food and other sources. Because depleted iron stores cannot meet the red blood cell's needs, fewer red blood cells develop. In this early stage of anemia, the red blood cells look normal but they are reduced in number. Then the body tries to compensate for the iron deficiency by producing more red blood cells, which are characteristically small in size. Symptoms of anemia develop at this stage.

Folic acid deficiency anemia
Folic acid anemia is especially common in infants and teenagers. Although this condition usually results from a dietary deficiency, it is sometimes due to inability