Confused About Vitamin B12?

Vitamin B12 is a water-soluble vitamin. Also known as cobalamin, it contains an atom of cobalt at the center of it's molecule giving it a red colour which has led it to occasionally be referred to as the "red vitamin". It's the only nutrient known to contain cobalt and the biggest and most complicated of all the vitamins. First isolated in 1947, it was the last vitamin to be discovered.

Major Functions:
It is needed for normal nerve cell activity, as it is vital in maintaining the health of the myelin sheath, a sort of insulation that surround nerve cells. B12, along with folic acid, is necessary for the synthesis of DNA, and the production and regeneration of red blood cells. It works synergistically with folic acid in lowering homocysteine levels, an amino acid that can contribute to cardiovascular disease in high levels. It is also known to promote growth, increase appetite, improve concentration, memory, and balance, and decreases irritability.

Food Sources:
B12 is synthesized by bacteria. The only reliable food sources of B12 are found in animal products as the animals obtain the vitamin through bacteria present in the soil on unwashed feed. It is particularly high in fish and shellfish. If we never washed our vegetables, we would be able to obtain B12 through the soil present on them, however, today, through chemical farming, even the soil is lacking in B12.
Bacteria in the large intestine are able to make B12, and some people think that they can obtain their B12 from these bacteria, however research shows that the bacteria produce B12 too far down the intestine for proper absorption.
This poses a challenge for vegans, who don't consume any animal products, and have to obtain B12 from fortified foods such as soy milk, tofu, nutritional yeast, and even most breakfast cereals are fortified with B12. Research into possible plant sources, as in fermented soy products such as tempeh, seaweeds such as nori, or algae such as spirulina, has shown that they contain significant amounts of compounds similar to B12, called B12 analogues, that can compete with and even inhibit absorption of the vitamin.
The amount of B12 actually needed by the body is around 2 mcg (micrograms)/day, but it is not absorbed very well, so much larger amounts need to be taken in. For example, 500 mcg can result in absorption of as little as 1.8 mcg. Absorption is also aided by calcium and iron.

Deficiency Symptoms:
Unlike other water-soluble vitamins, B12 isn't excreted quickly in the urine, but can be stored in the liver, kidneys, and other body tissues, 80% of it being stored in the liver. So deficiency symptoms sometimes don't show up for 5 or 6 years. Deficiency is more likely the result of poor absorption than of inadequate dietary intake. Absorption relies on an "intrinsic factor", which is a secretion from the lining of the stomach of a glycoprotein. Some people are unable to produce this intrinsic factor, and as we age, we produce less of it, making the elderly, or people with digestive disorders such as Celiac Disease or Crohn's Disease more susceptible to deficiency.
Some symptoms of deficiency can include: loss of appetite, diarrhea, numbness and tingling of hands and feet, paleness, shortness of breath, heart palpitations, fatigue, weakness, sore mouth and tongue, depression, irritability, hallucinations, headaches and ringing in the ears.
In cases of severe deficiency, pernicious anaemia can occur as the production of red blood cells is reduced, resulting in low levels of hemoglobin, thereby decreasing oxygen transportation in the blood.
Megaloblastic anaemia can occur also with B12 deficiency as it traps folate in a form that is not usable by the body, resulting in folate deficiency even when folate is present in sufficient quantities in the diet. When there is deficiency of B12 and folate, the synthesis of DNA is harmed. This is turn causes the red blood cells to form earlier than they are supposed to making them big, misshapen, and nucleated. Mature red blood cells have no nucleus. The hemoglobin content of these immature cells is poor.
Neurological damage can occur with B12 deficiency resulting in tingling of the arms and legs, difficulty walking, memory loss, disorientation, and dementia. When there is a deficiency, the myelin sheath that covers nerves is compromised. Many Alzheimer's patients are found to have low levels of B12, and symptoms often improve with supplementation.

Rich Food Sources of Vitamin B12 - mcg per 100g
Pig's liver 25
Fatty fish 5
White fish 2
Beef 2
Eggs 2
Cheese 1
Chicken 0.5
Milk 0.3

Choosing the Right B12 Supplement:
Since the symptoms of deficiency can be quite broad, one way of assessing B12 levels is by asking your doctor to run a serum B12 test. If deficiency is determined, there are many supplements to choose from commercially, but I would recommend looking for a liquid, sublingual product in the form of methylcobalamin, which is an acitve form of B12 that is very bioavailable. The most common alternative, cyanocobalamin has bound to a cyanide molecule in the purification process and does not occur in nature normally, therefore is not well absorbed. If the cause of deficiency is lack of intrinsic factor however, B12 injections, by prescription from a medical doctor may have to be administered. B12 is best absorbed when there are stomach acid secretions, so it is best to take your supplement with food.