Vitamin B-12 From the iThyroid Site
Vitamin B-12 is the cobalt-containing vitamin and levels can be judged by cobalt levels in the hair analysis. B-12 is critical for iron metabolism and a deficiency of B-12 will lead to anemia and probable hypothyroidism.
If you are hypo and supplementation with iron causes a problem, then suspect either a B-12 deficiency or a copper deficiency. If you are hyper and B-12 causes an increase in hyper symptoms, then suspect a copper deficiency (because B-12 will push iron metabolism and thereby suppress copper).
B-12 deficiency is very likely in persons with hypothyroidism and persons who have been taking copper and iron to recover from hyperthyroidism. Supplementation with high amounts of the other B vitamins, iron, and possibly manganese may use up B-12 creating a deficiency. This may be detected by experiencing adverse reactions to copper, iron, manganese, B vitamins, and many foods.
It is easy to determine a B-12 deficiency by taking a large dose (5000 mcg) since B-12 will have noticeable effects within several hours in a person who is deficient. If you are hypo, feel tingling in the hands, feet, or face, have a low pulse rate, feel your heart beating hard but not excessively rapid at night, or have adverse effects to iron, copper, or zinc, then try some B-12. If you are hyper and just commencing supplementation of copper and other supplements, do not take B-12. You may need to take some later as your hyper symptoms subside and you begin iron supplementation, but avoid it at the beginning.
Find an enteric coated 5000 mcg B-12 tablet. B-12 is destroyed by stomach acid so the enteric coating preserves it until it reaches the intestines where is can be absorbed. The sublingual types of B-12 apparently do not contribute a significant amount of B-12 to the body, but will provide a small but quicker energy boost.