Vitamin B12 is an essential nutrient that plays a major role in neurologic and mental functioning as well as in the production of folic acid. Folic acid plays a major role in reducing homocysteine levels and in cell repair (specifically DNA synthesis).
B12 is released from animal food sources by the action of Intrinsic Factor in the stomach and then it is absorbed from the last part of the intestines.
Because the stomach and intestines play a major role in absorption of B12, any disease of either of these organs can cause malabsorption of Vitamin B12. Patients who are on chronic acid suppressants (for example, Prilosec) owing to ulcers cannot synthesize Intrinsic Factor. Patients who have Crohn's disease, inflammatory bowel disease or celiac disease also have difficulties absorbing Vitamin B12.
Vitamin B12 is found primarily in animal food sources. Vegetarians, and vegans especially, do not ingest any food sources containing B12. The only exception is that blue-green algae is a source of B12.
The best sources of B12 include liver, clams, oysters, sardines, and egg yolks.
Symptoms or B12 deficiency include migraine headaches, numbness, tingling, depression and other mood disorders. In addition, B12 deficiency can present as anemia multiple sclerosis, infertility, fatigue, psychosis, and dizziness.
Although most physicians use serum B12 levels as the indicator for deficiency, it is actually an inaccurate test. Having circulating B12 in serum does not mean that it is utilized by the body's cells and the current standard is set too low. A normal serum B12 level should be at least 450pg, but may need to be higher depending upon your genetic makeup. A much better test for B12 adequacy is measuring methyl malonyl CoA levels in the urine.
Vitamin B12 supplementation comes in several forms: cyanocobalamin, hydroxocobalamin and methylcobalamin. B12 supplements do not require Intrinsic Factor for absorption. Methylcobalamin is the only active form, and all other forms need to be converted to the methylated version for it to fully function.
It is my opinion that anyone who is chronically ill should only use the methylcobalamin form. It requires energy to absorb and transform the non-methylated B12 and patients who are ill do not have the energy to do this. In addition, for those patients with absorption issues, oral vitamin B12 is ineffective and other routes of administration ( intramuscular injections and intravenous infusions) are far superior. Sublingual (under the tongue) administration in high enough doses will overcome the absorption difficulty as it is absorbed through the oral mucosa.
It should be noted that there has never been a report of adverse side effects from vitamin B12, nor has there been any toxicity associated from an overdosage. Excess B12 is stored in the liver.
For chronically ill patients, I recommend a minimum of 5000 mcg (5 mg) of sublingual B12 daily. To maintain good health, and for all vegetarians and vegans doses of 500 mcg to 1000 mcg should suffice.
Weston Price article about vitamin B12 - very comprehensive
KAY'S NOTE: You can find an SCD legal sublingual B12 at www.mercola.com