Compiled and reviewed  by
  Dr.Sanjana.V.B .Bhms,Dbrm,Cdn

  Vitamin B12

    Vitamin B12, also known as cobalamin, is a water-soluble essential vitamin that is derived chiefly from animal products such as meat, fish, dairy, and eggs. It is a vitamin very much important for the health of heart, red blood cells and brain. Severe deficiency of this vitamin may cause neurological deficits or problems.

 Vitamin B12 absorption needs intrinsic factor which is a glycoprotein produced by parietal cells of the stomach .Vitamin B12  is absorbed from the terminal ileum portion of small intestine.

 Vitamin B12 is very important for many vital functions of the body .It is a cofactor for enzymes that are involved in the synthesis of deoxyribonucleic acid (DNA), fatty acids, and myelin in human body. Therefore, Vitamin B12 deficiency may lead to ailments related to blood and nervous system.

Fatty acid synthesis is essential for energy generation and cellular metabolism.

Red blood cells are formation and maturation require vitamin B12 and its deficiency leads to macrocytic anaemia. The red blood cells become bigger and they cannot move from bone marrow to the circulation and anaemia results.

Sources of vitamin B12

•     Milk

•     Cheese

•     Yogurt

•     meat

•     fish-salmon, trout

•     eggs

•     clams

•     shiitake mushroom

What are the causes leading deficiency of vitamin B12 in the body?

    Vitamin B12 deficiency may occur from dietary insufficiency, malabsorption, or lack of intrinsic factor [secreted by parietal cells of stomach], or when liver stores are depleted of vitamin B12. Normally excess vitamin B12 is stored in liver.

Poor intake of vitamin B12 is usually found in vegetarians as vitamin B12 is a nutrient available chiefly from animal sources like meat, milk and eggs. Although some vegetables like mushrooms, edible algae are plant sources of vitamin B12, it is not easily available to all and not a part of traditional diet in all sections of the global population. Hence poor intake leads to deficiency.

Intrinsic factor deficiency also causes deficiency of vitamin B12 in a small group as a result of malabsorption. Vitamin B12 is normally absorbed from ileum of small intestine & diseases like Chron’s disease, ulcerative colitis leads to poor absorption and thus the deficiency of the vitamin.

Who are at risk of vitamin B12 deficiency?

The deficiency is more common among the following groups:

•     Persons with family history of vitamin B12 deficiency anaemia.

B12 deficiency due to pernicious anemia is more common in people of Northern European ancestry.

•     Malabsorption causes deficiency in people with partial or complete surgical removal of intestine or have done gastric bypass surgery.

•     Autoimmune diseases cause production of antibodies to intrinsic factor of parietal cells of stomach. Anti-intrinsic factor antibodies bind to and inhibit the effects of intrinsic factor, resulting in an inability of B12 to be absorbed by the terminal ileum.

•     Damage to small intestine-

People with inflammatory bowel diseases, Chron’s disease, and ulcerative colitis suffer from vitamin B12 deficiency due to poor absorption of the vitamin, as terminal ileal portion of small intestine is damaged.

•     Inflammation from celiac disease or infection with the tapeworm Diphyllobothrium latum causes vitamin B12 deficiency. Having Chron’s disease and HIV leads to vitaminB12 deficiency eventually.

•     Old age enhances the risk for all vitamins and mineral deficiencies including vitamin B12. Taking strict vegetarian diets also poses risk for the deficiency as vegetables do not contain adequate amount of the vitamin and only a few species of algae and mushrooms have moderately good vitamin B12 content which are not accessible to all.

•     Vitamin B12 intake must be enough during pregnancy for the healthy growth of foetus and its nervous system especially during the first trimester of pregnancy. Both vitamin B12 and folic acid intake is essential for mothers to prevent miscarriage and neural tube defect in the baby. Researchers conclude the fact that vitamin B12 deficiency is associated with a significantly increased risk for neural tube defects.

  The recommendations for vitamin B12 intake before becoming pregnant is >300ng/L.

 Symptoms of vitamin B12 deficiency

Tingling feelings or pain

Trouble walking

Uncontrollable muscle movements

Confusion, slower thinking, forgetfulness, and memory loss

Mood or mental changes, such as depression or irritability

Problems with smell or taste

Vision problems

Diarrhea and weight loss

Glossitis, which is a painful, smooth, red tongue

In case of insufficiency of vitamin B12, blood cells do not form properly inside the bone marrow within your bones. These blood cells die much earlier than normal, leading to anemia. Do not ignore the symptoms of vitamin B12 deficiency as it may lead to homocysteine amino acid  accumulation and risk of heart attack, stroke and dementia or loss of memory.

The assessment of vitamin B12 status forms part of the screening process for dementia or loss of memory.

Relationship between Vitamin B12 & homocysteine.

 Homocysteine is an amino acid. In a healthy person, homocysteine levels are around five to 15 micromoles per liter (mcmol/L).

Vitamins B12, B6 and folate break down homocysteine to create other chemicals which are not harmful to your body. When homocysteine interacts with the B vitamins, it is converted in to two substances:

1] Methionine, an essential amino acid and antioxidant that synthesizes proteins.

2] Cysteine, a nonessential amino acid synthesized from methionine that reduces inflammation.

But if homocysteine levels are high in your blood, it means you have a vitamin B12,B6 or folate deficiency.

  Elevated homocysteine levels may increase your risks for dementia, heart disease and stroke.

You may need a homocysteine blood test if you have symptoms of a vitamin B deficiency as mentioned above. Aging, alcohol and smoking can increase your homocysteine levels.

 Dietary supplementation of vitamin B12, folic acid and B6 can help you reduce homocysteine related risks.

References

1.        https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/

2.       https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3257642/

3.       https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1283514/

4.     https://www.nhlbi.nih.gov/health/anemia/vitamin-b12-deficiency-anemia#:~:text=Vitamin%20B12%E2%80%93deficiency%20anemia%2C%20also,white%20blood%20cells%2C%20and%20platelets.