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Vitamin B12 belongs to the group of vitamin B complex. It is essential for vital bodily processes such as metabolism, DNA synthesis, the production of red blood cells, and healthy functioning of the nervous system. Its dietary sources include eggs, poultry, meat, shellfish, milk, dairy products, fermented soy products, and seaweed. People who follow a strict vegetarian diet are more likely to have the deficiency. In some cases, people who undergo weight loss surgery lose the ability to absorb this vitamin which in turn might lead to a deficiency. Absorption of this vitamin might also get adversely affected in people who have been diagnosed with celiac or Crohn's disease.

Symptoms
  • Nutritional deficiencies, iron, and folic acid can cause canker sores
  • Anemia
  • Diarrhea
  • Numbness or tingling sensation in toes or fingers
  • Loss of appetite
  • Sore tongue, mouth, and throat
  • Bleeding gums
  • Frequent headaches
  • Lightheadedness
  • Weakness
  • Loss of balance
Who is Not a Good Candidate

People who have the deficiency are advised to take necessary (Cyanocobalamin) supplements. Though vitamin B12 toxicity is rare, adverse effects might be observed in the following cases:
  • People who are allergic to cobalt or cobalamin could develop an allergic reaction on taking these supplements. In severe cases, the affected person might experience symptoms such as hives, wheezing, breathing difficulty, swelling, etc.
  • Leber's hereditary optic neuropathy is a medical condition affecting the eyes. It is a hereditary condition wherein the degeneration of the optic nerve gives rise to progressive loss of vision. The use of cobalamin supplements is associated with worsening of the symptoms.
Side Effects

When taking the supplement by mouth, applied directly over the skin, through the nose, or as an injection, it is relatively safe. However, there can be certain side effects associated with it.
  • Pain and warmth at the site of injection
  • Nausea
  • Headache
  • Upset stomach
  • Mild diarrhea
Recommended Dosage
Vitamin B12 is an important vitamin required by the body, and to avoid deficiency or an overdose, one needs to take it in the recommended dosage.

Age Group Dosage (micrograms per day)
0 - 6 months 0.4
7 - 12 months 0.5
1 - 3 years 0.9
4 - 8 years 1.2
9 - 13 years 1.8
14 years and older 2.4

Source: The Food and Nutrition Board at the Institute of Medicine

Though there's no tolerable upper intake limit for this vitamin, and being a water-soluble vitamin, the excess is flushed out with urine, it would be in one's interest to take these supplements as per the recommended dosage.

Disclaimer: This article is for informative purposes only and does not in any way attempt to replace the advice offered by an expert on the subject.