Vitamin B12 deficiency anemia, also known as pernicious anemia, is a condition in which the body does not make enough healthy red blood cells. Red blood cells contain a protein called hemoglobin, which gives blood its red color. More importantly, it helps the blood transport oxygen from the lungs to the tissues in other parts of the body.

Individuals with this disease have low oxygen in their blood. As a result, they often feel tired as their bodies cannot make enough energy. In severe cases of the disease, the insufficient oxygen in the blood can cause serious and sometimes fatal damage to the heart and other important organs in the body.

This type of anemia results from vitamin B12 deficiency, which may be caused by low dietary intake of the vitamin and absorption disorders. An absorption disorder may be caused by reduced stomach acid, lack of intrinsic factor, or diseases that impair absorption of nutrients in the small intestine.

So, who is most at risk and why? Adults age 50 and older are at INCREASED risk of developing vitamin B12 deficiency, primarily because of reduced stomach acid. In foods like meat, fish, and eggs, this vitamin is bound to protein, and stomach acid (like hydrochloric acid) is needed to separate it. Reduced stomach acid decreases the body's ability to release the vitamin from protein. An estimated 30% of older adults have some absorption disorder that reduces their absorption of the vitamin. For this reason, the Food and Nutrition Board of the Institute of Medicine recommends that older adults should meet their daily requirement mainly from fortified foods or supplements like multivitamins and B complex.

An individual may also be at increased risk of deficiency due to lack of Intrinsic factor, a class of protein produced by the cells found in the lining of the stomach. After vitamin B12 has been separated from food, it must bind to this protein before the body can absorb it. Without the protein, the vitamin is excreted in stool. People who do not produce this protein may have an autoimmune reaction in which abnormal antibodies, produced by overactive immune system, attack and destroy it.

Furthermore, diseases like inflammatory bowel disease (e.g. Crohn's disease) can cause deficiency. Crohn's disease causes inflammation of the digestive system, especially the lower part of the small intestine (or ileum) where nutrients are absorbed. Certain surgeries that result in the removal of ileum increase the risk of deficiency. Strict vegetarians (or vegans) are also at risk because plant-based foods are poor sources of the vitamin and over time may cause deficiency and anemia.

An anemia due to vitamin B12 deficiency reduces the number of healthy red blood cells in the blood. This means that patients with the disease do not carry enough oxygen in their blood, so they often feel tired. Certain groups in the population are more susceptible to the disease than others, and these groups include adults age 50 and older, people with inflammatory bowel disease or overactive immune system, and strict vegetarians. The current official recommendation is that these groups should meet their daily requirement mainly from fortified foods or supplements like B complex and multivitamins.