"Vitamin B12 deficiency is very common and almost two third of the population in civilized world has this deficiency.
Historically this vitamin was obtained from our contact with soil through hands and feet and drinking ground water. Now that we avoid such contacts and all municipal supply of water is chlorinated, which kills B12, there are no natural sources available. It is for this reason, it along with vitamin D, is the most fortified nutrient in processed foods. B12 deficiency can be due to dietary deficiency or compromised absorption or both. Vitamin B12 is stored in the liver. It acts as a coenzyme for many body functions. It is critical for the production of red cell, nerves and DNA production, brain function and cardio vascular health. Many people do not consume enough B12 and some are not able to absorb enough. Both result in vitamin B12 deficiency. Common symptoms of B-12 deficiency include:
* Fatigue weakness and a general sense of tiredness.
* Skin, hair and nail problems.
* Paleness and Jaundice.
* Moodiness leading to anxiety and depression.
* Nerve damage causing numbness and tingling sensation in hands and feet
* Neurological damage causing muscle weakness, loss of balance and coordination.
* Dementia and memory loss.
* Digestive issues causing nausea, vomiting, heartburn and enlarged liver.
* Some people have an autoimmune disease called Pernicious Anemia, in which the protein necessary for absorption of B-12 is destroyed by the body. People with Inflammatory Bowl Disease and Celiac disease are also more susceptible to B12 deficiency.

B12 is produced by bacteria found in soil as well as in the guts of animals (including humans) but in order for the bacteria to make B12 the soil needs to contain the mineral cobalt.

B12 supplements are of two kind cyanocobalamine and methylcobalamine. Required dietary allowance fo B12 is 2.4 mcg per day but considering that absorption is very limited, it is required that one takes about 80 mcg each day or 2,000 mcg weekly. The absorption of B12 is not a linear function so just because you take twice doesn’t mean you absorb twice. That explains the discrepancy between 2.4 mcg requirement vs. 80 mcg daily or 2,000mcg weekly recommendation. Since B12 is a water-soluble vitamin, it's generally considered safe, even at high doses. The risk of toxicity is very low.

A few plant foods naturally contain trace amounts of bio active vitamin B12 like Nori Seaweed, Tempe, some forms of Algae and some variety of mushrooms but more research is needed to understand absorption by humans from such source.

Vitamin B12 deficiency is a very serious problem leading ultimately to anemia, neuropsychiatric disorders, irreversible nerve damage, and high levels of artery-damaging homocysteine in the blood.

Its important that everyone should be taking daily requirements of B12 supplement".