An essential nutrient, Vitamin B12 is needed for building proteins in the body, red blood cells, and normal function of nervous tissue - it is vital in maintaining the health of the insulation sheath that surrounds nerve cells.
The amount of Vitamin B12 we actually need is very small, but unfortunately the body does not absorb it very well. Thus we need to intake larger amounts to be sure we have sufficient.
The best dietary sources of vitamin B12 are liver and kidneys, while eggs, cheese and some fish also supply small amounts. Vegetables and fruits, however, are very poor sources.
It is thus not unusual for strict, long-term vegetarians to be deficient. Deficiencies are also found in many elderly people, as their body's ability to absorb the vitamin from the small intestine declines rapidly with age.
Although it is water-soluble, it is not excreted quickly in the urine, but rather accumulates and is stored in the liver, kidney and other body tissues. It is therefore possible that a deficiency might not manifest itself for 5 or 6 years if someone's diet is supplying inadequate amounts.
The most common problem from deficiencies is pernicious anaemia, a disease characterized by large, immature red blood cells. Unfortunately a deficiency often first manifests itself in the form of neurological dysfunction that is almost indistinguishable from senile dementia and Alzheimer's disease, making diagnosis in the elderly particularly difficult.
Other symptoms of a shortage include asthma, depression, AIDS, multiple sclerosis, tinnitus, diabetic neuropathy and low sperm counts.
Oral supplementation is simple, safe and effective, however.