The term vitamin B12 (cobalamin) is used in a couple different ways. Vitamin B12, a member of the B-vitamin family, is a term used collectively to represent a group of cobalt-containing compounds known as corrinoids. The principal cobalamins are cyanocobalamin, hydroxocobalamin, and the two coenzyme forms of vitamin B12, methylcobalamin, and 5-deoxyadenosylcobalamin (adenosylcobalamin). However, the term vitamin B12 is usually used to refer to only one of these forms, cyanocobalamin, which is used to fortify foods and in nutritional supplements.

In combination with folic acid and vitamin B6 vitamin B12 serves to control homocysteine levels. Excessive amounts of homocysteine may increase the risk of stroke, coronary heart disease, osteoporosis, and Alzheimer’s disease.

Vitamin B12 deficiency may result negative in hematological, neurological, and gastrointestinal conditions. The hematological systems and signs of B12 deficiency include a decrease in red blood cell count, skin discolorations, decreased energy, fatigue, shortness of breath, and palpitations. Severe B12 deficiency can also result in anemia.

Even in the absence of anemia, the neurological effects of vitamin B12 deficiency can still occur. This is especially true for the elderly. In theses cases, vitamin B12 deficiency can affect the peripheral nerves, and in later stages, even the spinal cord itself. Signs of neurological conditions caused by B12 deficiency include tingling and numbness in the extremities, loss of sensation, spacticity, Babinski's responses, visual impairment, bowel control issues, insomnia, impotence, irritability, depression, memory loss, and dementia.

Gastrointestinal effects of B12 deficiency may include diarrhea, constipation, abdominal pain, excessive flatulence, and a burning sensation on the tongue.

Additional conditions that have been associated with vitamin B12 deficiency include anorexia, weight loss, age-related hearing loss, Alzheimer’s disease, and pernicious anemia.

Dosage Recommendations

The majority of us do not need to take vitamin B12 supplements. However, as indicated above, vitamin B12 can and should be taken in connection with deficiency related conditions. Recommended doses include:

• For vegans take 2 to 3 mcg of supplemental B12 per day.
• For pernicious anemia take 1,000 mcg (orally) per day.
• Absorption of vitamin B12 is reduced as you get older. Some research suggests that elderly people may benefit from 10 to 25 mcg per day of vitamin B12.