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Vitamin B12 is vital for our body for the proper functioning of the brain and nerves and manufacturing of red blood cells and DNA. It is a water-soluble vitamin that travels across the bloodstream and keeps the nerves and cells healthy. Foods are the natural source of vitamin B12. It is mainly found in animal products like eggs, beef, pork, lamb, meat and fish and dairy products like yoghurt and milk. Fortified breakfast cereals are also a good example of vitamin B12 source, especially if you are a vegetarian.
Vitamin B12 is known to have many health benefits, and the deficiency of B12 may cause several neurological disorders like memory loss, blurred vision and anaemia. There are limitations on the use of its supplements depending on an individual's age, medical conditions and dietary habits. It also varies when the woman is pregnant or lactating. 
Cause Of Vitamin B12 Deficiency
There are two main causes for the deficiency of vitamin B12. They are as follows:
1. Insufficient consumption of vitamin B12: It usually occurs in people who are vegans or people who do not consume meat or other animal products. The only option available for them is foods fortified with B12 like soy products and cereals. 
2. Body's incapability to absorb and store the vitamin: They are caused due to several reasons like the following:
- Overgrowth of bacteria in the small intestine due to conditions like diabetes and diverticula. 
- Inflammatory bowel disease
- Medications like metformin which are used in diabetes 
- Exposure to laughing gas (Nitrous oxide)
- Celiac disease or other malabsorption diseases
- Surgery of the small intestine
- Lack of intrinsic factor, a kind of protein that takes vitamin B12 to the intestines to be absorbed. 
Symptoms Of Vitamin B12 Deficiency
The deficiency of Vitamin B12 can trigger symptoms similar to the nervous system and brain disorder. As the deficiency often leads a person to anaemia, the symptoms are also similar to it. Common symptoms of vitamin B12 include:
Risk Factors Of Vitamin B12 Deficiency
Excluding animal food products possesses greater risks of vitamin B12 deficiency. This condition can also occur under pernicious anaemia (an autoimmune disease), Crohn's disease, chronic alcoholism and other conditions in which the body is unable to absorb vitamin B12. 
Complications Of Vitamin B12 Deficiency
The deficiency of B12 can easily be treated by consuming foods enriched with it. However, if the condition lasts long, it may cause serious complications like the following:
Diagnosis Of Vitamin B12 Deficiency
Before performing any tests, the medical expert will ask for the patient's diet, family history (for any autoimmune disorder) and medical history which may be responsible for vitamin B12 deficiency. Tests involved in diagnosing the condition are as follows:
- Blood tests: To check for the deficiency of B12 by measuring the levels of iron and folate, levels of methylmalonic acid and the presence of intrinsic factor 
- Bone marrow biopsy: To determine the cause of abnormalities in RBCs
- Schilling test: To find out how well a person's body can absorb the vitamin 
- Endoscopy: To check for any damage in the stomach cells which is responsible for the lack of intrinsic factor
Treatment For Vitamin B12 Deficiency
The treatment for vitamin B12 includes the following:
- Supplements: For vegetarians and older people or for people who are unable to take the vitamin from the source of meat, vitamin B12 supplements make an ideal option. However, before starting the medication, consult a medical expert for the recommended dosage. 
- Vitamin B12 injection: The injections of vitamin B12 are used when the supplements are not well absorbed when taken by mouth or in case of severe symptoms like muscle weakness.
- Antibiotics: When the deficiency is due to the overgrowth of bacteria.
- Blood transfusion: In case of severe anaemia when the RBC count is too low.
Note: A high intake of vitamin B12 supplements and injections can be toxic and may result in several side effects. Consult a medical expert before starting it.
How To Prevent Vitamin B12 Deficiency
- Eat foods rich in vitamin B12 like meats and eggs.
- Take its supplements on time.
- If you are unable to have vitamin B12 rich foods, opt for foods rich in folic acid, iron and vitamin C like spinach, orange, beans, broccoli, nuts, etc., as they too are essential for the production of healthy red blood cells.
- Follow a well-balanced diet.
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-  3. Murphy, M. F., Sourial, N. A., Burman, J. F., Doyle, D. V., Tabaqchali, S., & Mollin, D. L. (1986). Megaloblastic anaemia due to vitamin B12 deficiency caused by small intestinal bacterial overgrowth: possible role of vitamin B12 analogues. British journal of haematology, 62(1), 7-12.
-  4. Kibirige, D., & Mwebaze, R. (2013). Vitamin B12 deficiency among patients with diabetes mellitus: is routine screening and supplementation justified?. Journal of Diabetes & Metabolic Disorders, 12(1), 17.