nutritional defects (vitamin B12 is mainly from animal sources, and vegans may require supplementation)
chronic liver diseases
decreased production of intrinsic factor (this disease entity is called pernicious anemia)
intestinal malabsorption (due to an enteritis, celiac disease or other causes).
fish tab worm infestation (Diphyllobothrium latum)

Hematological findings

The blood film can point towards vitamin deficiency:

Decreased red blood cell (RBC) count and hemoglobin levels
Increased mean corpuscular volume (MCV, >100 fl) and mean corpuscular hemoglobin (MCH)
The reticulocyte count is normal
The platelet count may reduced.
Neutrophil granulocytes may show multisegmented nuclei ("senile neutophil"). This is thought to be due to decreased production and a compensatory prolonged lifespan for circulating neutrophils.
Anisocytosis (increased variation in RBC size) and poikilocytosis (abnormally shaped RBCs).
Macrocytes (larger than normal RBCs) are present.
Ovalocytes (oval shaped RBCs) are present.
Bone marrow (not normally checked in a patient suspected of megaloblastic anemia) shows megaloblastic hyperplasia.

Analysis

The Schilling test is often performed to determine the nature of the vitamin B12 deficiency.

Iron-deficiency anemia

The most common form of anemia results from a deficiency of iron, a key component for the production of hemoglobin. In infancy, iron-deficiency anemia is a problem for infants who are not breastfed, or who are born in developing countries where adequate nutrition or medical attention may not be available. Researchers have discovered that one technique to prevent iron-deficiency anemia among newborns is to wait for about one minute after birth before clamping the umbilical cord. This enables more blood to flow from mother to infant.

Toddlers and young children may develop anemia when they are introduced to solid foods and the variety of their diet becomes important. According to Ibrahim Parvanta, a nutritionist with the Centers for Disease Control and Prevention in Atlanta, Georgia, children ages 6-24 months may have insufficient iron stored in their systems to meet their bodies' needs during this phase of rapid physical growth. He estimates that approximately 9% of children in this age group have at least mild iron deficiency. Symptoms of iron-deficiency anemia are fatigue, paleness, headaches, dizziness, and lowered immunity. In infants and children, iron-deficiency anemia can be a serious condition, resulting in impaired physical and mental development.

Iron requirements increase during periods of rapid growth and at the onset of menstruation in girls. Anemia in adolescence is most commonly iron-deficiency anemia. Teenage girls, concerned about their weight, often have diets that are inadequate in iron; an estimated one in four adolescent girls has iron deficiency.

Treatment of iron deficiency usually begins with a doctor's recommendation to increase iron in the diet, or perhaps with a prescription for iron supplements. Iron-rich foods are of two types. The first type of food contains heme iron, which is easier for the body to absorb. These include liver, red meat, poultry, and fish. The second type contains nonheme iron, less easily absorbed by the body, and includes dried apricots, prunes, dates, raisins, beans, tofu, nuts, and leafy green vegetables, such as spinach. Absorption of iron by the body is aided by vitamin C, so adding citrus fruits to an iron-rich meal improves the body's ability to make use of the iron. Using iron cookware to prepare foods also increases the iron content of foods. In general, it is preferable to treat anemia by adding iron-rich foods to the diet, since some people experience nausea when taking iron supplements.

Iron in large quantities is also toxic. The National Capital Poison Control Center at Georgetown University in Washington, DC, reports that from 1988-1992, accidental poisoning from overdose of iron supplements accounted for about 17% of all children's deaths reported to poison control centers. Iron supplements should be considered poisonous, and kept out of the reach of children.

Thalassemia

Recommended Dietary Allowances (RDAs) for Iron
Recommended Dietary Allowances (RDAs) for Iron
Infants up to 6 months: 6 mg

Children 6 months to 10 years: 10 mg

Females ages 11 to 50: 15 mg

Pregnant women: 30 mg

Women 60 and over: 10 mg

Males ages 10 to 18: 12 mg

Men 18 and over: 10 mg

Thalassemia is a genetic disorder of the blood in which the red blood cells are small and fragile. Thalassemia is found among people of Mediterranean, Middle Eastern, or Southeast Asian descent, and is sometimes referred to as "Mediterranean anemia." The most severe form, known as beta-thalassemia, thalassemia major, or Cooley's anemia, develops during infancy with slow physical growth and jaundice. The spleen and bone marrow may become enlarged, causing abnormal skeletal development. If untreated, thalassemia leads to death in later childhood or adolescence. Treatment includes blood transfusions or bone marrow transplants. However, a dangerous side effect of transfusions is build-up of excess iron in the system.

Sickle-cell anemia

Sickle cell anemia is a genetic disorder that most commonly affects African Americans, but is also found among those of Mediterranean descent. Victims of the disorder have crescent-shaped red blood cells. The unusual shape prevents the cells from carrying oxygen efficiently and causes the cells to become lodged in the capillaries, causing a person intense pain.

Aplastic anemia

Aplastic anemia is characterized by an insufficient supply of all blood cell types, including an abnormal or insufficient production of red cells in the bone marrow. Aplastic anemia, diagnosed in 5,000-6,000 Americans a year, can result from severe viral infections, diseases of the immune system, and hepatitis. It is also associated with cancer therapies such as chemotherapy or radiation therapy, both of which adversely affect the bone marrow's ability to produce red blood cells. If not successfully treated, aplastic anemia results in death for about 85% of those afflicted by the condition.

Aplastic anemia is considered a medical emergency, and a bone marrow transplant is performed as quickly as possible after diagnosis. Bone marrow transplantation from a family member is most successful and is recommended for younger patients. Transplantation from unrelated donors has only been achieved in very small children.