Vitamin B12

​Function: 
Vitamin B12 is needed to modify proteins and breakdown fat.  B12 also works together with Folate and is vital forneural function, proper cell replication and division, and blood cells. 

Deficiency: 
Vitamin B12 deficiency leads to megaloblastic macrocytic anemia and the symptoms of skin pallor, insomnia, tingling and numbness in extremities, fatigue, weakness, shortness of breath, irregular heartbeat, memory loss, difficulty concentrating, disorientation, and possibly dementia. 

Sources & Absorption:
Vitamin B12 is naturally produced by microorganisms.  The way we naturally consume B12 is through “contaminated” plants (which is not likely with current food safety practices), or through animal products (with the animals having already obtained the B12 through microorganisms).  Meats, fish, poultry, and eggs are good sources of B12 and dairy products are moderate sources.  Individuals choosing a vegan lifestyle will need to supplement B12.  B12 requires a glycoprotein called intrinsic factor for absorption. Intrinsic factor is produced by the stomach and production reduces with age, therefore some older individuals also require supplementation.

Toxicity:
Unlike other water-soluble vitamins, B12 is stored by the body and therefore does not require daily consumption.  No toxicity from B12 consumption or supplementation has been shown.

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* This information is not intended to encourage self-supplementation.   As you will read in individual nutrient content, self-supplementation can be unnecessary or even dangerous.  I highly recommend micro-nutrient blood testing before choosing to take any supplements that are not whole-foods based.
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References:
Gropper SS, Smith JL, Groff JL. Advanced nutrition and human metabolism. 5th ed. Belmont, CA: Wadsworth; 2009.
Mahan L, Escott-Stump S, Raymond J. Krauses's food and the nutrition care process. 13th ed. St. Louis, Missouri: Elsevier Saunders; 2012.