Deficiency of vitamin B12 significantly affects the functioning of the nerves associated neurological functioning. The following are the signs and symptoms of vitamin B12 deficiency:

• Fatigue
• Weight loss
• Palpitations
• Development of sore in the mouth and tongue
• Diarrhea
• Problems with menstrual cycle
• Increased susceptibility to infections
• Development of yellowish coloration of skin

In more advanced stages, when the deficiency continues for a prolonged duration, then the nervous system can get affected, and would showcase the following symptoms [6]:

• Generalized muscular weakness
• Development of tingling and numbness in the hands and feet
• Calf muscle become tender
• Bouts of confusion, irritability and forgetfulness
• Experiencing grave difficulty in walking properly 

A preliminary physical examination will be done, to study for the signs of vitamin B12 deficiency. In addition, the following tests would also be carried out to diagnose the condition [7]:

• Blood tests: This is done to analyze the levels of vitamin B12 and RBCs. The shape of the red blood cells would also be taken note of, in order to check for other accompanying disorders. Blood tests also furnish information, on whether the individual is suffering from pernicious anemia or not.
• Biopsy of bone marrow: This is done to rule out any possibility of development of anemia, and other abnormalities concerning the red cells.
• Breath test: This is one of the new tests, to determine vitamin B12 deficiency. It is one of the simpler and cheaper techniques to diagnose the deficiency, which would also help in early diagnosis of the condition, thereby preventing onset of other complications [8].

Supplementation of vitamin B12, either orally or intravenously, is employed for correcting its deficiency. The vitamin supplement is available either as a single component, or in combination with other nutrients. Complete repletion of liver stores with vitamin B12 requires about 20 injections, along with injections given on monthly basis for maintenance of the stores [9].

Vitamin B12 injections are either given through the subcutaneous route, or intramuscularly. These injections contain hydroxycobalamin, cyanocobalamin or methycobalamin. Administration of vitamin B12 through the parenteral route, has been shown to enhance the absorption of this vitamin [10].

Hypokalemia is a common occurrence in patients, who are given supplements of vitamin B12. This is so because potassium is excessively used by the new hematopoietic cells for the process of growth and division.

Individuals with vitamin B12 deficiency have a good prognosis, if the treatment is initiated within 6 months of experiencing the symptoms. Failure to do so can cause permanent damage to the nerves, and other associated problems.

The following are the various factors responsible for causing vitamin B12 deficiency:

• Diet: Consuming a diet deficient in vitamin B12 can cause deficiency to set in. It has been stated that vegans and vegetarians are at an increased risk to develop deficiency of this vitamin, because the human body cannot absorb the form of vitamin B12 that is present in the plant sources.
• Disease: Certain underlying disease conditions such as celiac disease, Crohn disease, and megaloblastic anemia, can interfere with the absorption of vitamin B12, causing its deficiency to set in [2].
• Alcoholism: Alcohol drinkers suffer from malnutrition, due to poor absorption of nutrients from food.

The exact prevalence of vitamin B12 deficiency is unknown. However, it has been estimated that about 300,000 – 3 million individuals can get affected by its deficiency. It was also reported that about, 3 to 16% of the population had a vitamin B12 level less than 200 pg/mL (using the cut offs of radioassay techniques). Using cut off value of 300 pb/mL for elderly population, vitamin B12 deficiency was found in 21% of population. In European countries, vitamin B12 deficiency is found in approximately 1.6 to 10% individuals [3].

After ingestion of foods containing vitamin B12, the low pH of the stomach cleaves cobalamine from dietary protein. This then binds to gastric R binder, and reaches the duodenum and jejunum, where the enzymes present in pancreas digest the complex, and release cobalamin. Following this event, free cobalamin binds with the gastric intrinsic factor (IF). The secretion of IF is dependent on secretion with hydrochloric acid. Therefore, during conditions of achlorhydria, when the secretion of IF is reduced, lead to deficiency of vitamin B12 [4] [5].

Vegans and vegetarians, who do not consume eggs, are at an increased risk for developing vitamin B12 deficiency. Such individuals should consider consuming several breakfast cereals, which are fortified with vitamin B12. In addition, certain types of soy milk are also fortified with the vitamin, which if consumed, can help maintain the blood levels of vitamin B12. Individuals can also consider popping in multivitamin, which contain about 6 micrograms of vitamin B12, which is sufficient to cover an individual’s daily requirement.

Deficiency of this vitamin, can therefore lead to anemia, and can also cause serious damage to the nerve and brain functioning. Vitamin B12 deficiency occurs at all age groups, and often goes undiagnosed due to its complex etiology. According to the research conducted by the Framingham Offspring Study, it was postulated that deficiency of vitamin B12 primarily occurs due to its improper absorption, rather than its poor consumption [1].

Definition: Vitamin B12 deficiency is characterized by low levels of vitamin B12 in the body. It is an essential vitamin required for optimal functioning of nervous tissues. Therefore, deficiency of the vitamin can have serious consequences on the neurological functioning.

Cause: A diet deficient in vitamin B12, and all those factors that interfere with the absorption of the vitamin, causes its deficiency to set in. In addition, various other underlying disease conditions, such as pernicious anemia, and condition of chronic alcoholism, can cause deficiency of vitamin B12 to develop.

Symptoms: In the initial stages, vitamin B12 deficiency manifests with signs of fatigue, weight loss, diarrhea, sores in the mouth and tongue, menstrual disorders and increased susceptibility to infections. In advanced stages, when neurological problems set in, individuals experience confusion, irritability, forgetfulness, tingling sensation in the hands and feet, and difficulty in walking properly.

Diagnosis: Vitamin B12 deficiency is diagnosed through blood tests and bone marrow biopsy. These tests also help determine the shape of the red blood cells, and presence of pernicious anemia. A new test known as breath test is also used for diagnosis of vitamin B12 deficiency.

Treatment: The condition is treated with supplements, administered either through the oral or intravenous route. Parenteral administration of vitamin B12 has been shown to enhance the absorption of this vitamin.

1. Nielsen MJ, Rasmussen MR, Andersen CB, Nexø E, Moestrup SK. Vitamin B12 transport from food to the body's cells--a sophisticated, multistep pathway. Nat Rev Gastroenterol Hepatol. May 1 2012;9(6):345-54.
2. Antony AC. Megaloblastic anemias. In: Hematology: Basic principles and practice, 4th ed, Hoffman R, Benz EJ, Shattil SJ, et al. (Eds), Churchill Livingstone, New York 2005. p.519.
3. Pflipsen MC, Oh RC, Saguil A, Seehusen DA, Topolski R. The prevalence of vitamin B(12) deficiency in patients with type 2 diabetes: a cross-sectional study. J Am Board Fam Med. Sep-Oct 2009;22(5):528-34.
4. Scalabrino G, Peracchi M. New insights into the pathophysiology of cobalamin deficiency. Trends Mol Med 2006; 12:247.
5. Andrès E, Serraj K, Zhu J, Vermorken AJ. The pathophysiology of elevated vitamin B12 in clinical practice. QJM 2013; 106:505.
6. Healton EB, Savage DG, Brust JC. Neurologic aspects of cobalamin deficiency. Medicine (Baltimore). Jul 1991;70(4):229-45.
7. Balducci L. Epidemiology of anemia in the elderly: information on diagnostic evaluation. J Am Geriatr Soc. Mar 2003;51(3 Suppl):S2-9.
8. Green R, Kinsella LJ. Current concepts in the diagnosis of cobalamin deficiency. Neurology 1995; 45:1435.
9. Hathcock JN, Troendle GJ. Oral cobalamin for treatment of pernicious anemia? JAMA 1991; 265:96.
10. Butler CC, Vidal-Alaball J, Cannings-John R, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency: a systematic review of randomized controlled trials. Fam Pract 2006; 23:279.