The possible causes of vitamin B12 deficiency are:
Pernicious anemia is caused by an autoimmune disease; a person's own immune system attacks good parts of the body, as if they were bacteria or viruses.
The immune system of patients with pernicious anemia creates antibodies which attack the lining of the stomach, damaging cells that produce intrinsic factor. Intrinsic factor is a substance that is secreted by the gastric mucous membrane (lining of the stomach) and is vital for the absorption of vitamin B12 in the intestines. If the production of intrinsic factor is undermined, vitamin B12 cannot be absorbed into the body properly.
Patients with Crohn's disease, as well as people who have had their bowels surgically shortened, may have problems absorbing vitamin B12 into their bloodstream. Short bowel syndrome is a term used for people who have had their bowel shortened (half or more of their small intestine removed). Patients with short bowel syndrome typically experience diarrhea, cramping and heartburn. It is not uncommon for individuals to become malnourished because what is left of the small intestine cannot absorb adequate quantities of vitamins, water and other nutrients.
Some people who follow a vegan diet may suffer from B12 deficiency if they do not eat fortified foods, or some types of yeast. Japanese and Italian scientists wrote in the Journal of Agricultural Food Chemistry that vegetarians and vegans are much more likely to develop vitamin B12 deficiency. The human body cannot use the plant-based form of the vitamin, they explained.
Chronic alcoholism may also be a cause of B12 deficiency, according to the National Library of Medicine3.
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