Generally people talk of vitamin overdose but with the case of vitamin B12 it is just the opposite. Especially vegans and elderly subjects are most likely to suffer from this vitamin deficiency declares a study from the Harvard Medical School.
The symptoms of B12 deficiency are subtle cognitive and neurological changes. A serious deficiency may cause dementia or anaemia. Breast-fed infants of mothers with a B12 deficiency are at risk for severe developmental abnormalities and irreversible neurological damage.
Apart from fortified breakfast cereals, the only reliable dietary sources of vitamin B12 are animal-derived products. Therefore the most affected people are vegans, but even vegetarians who eat eggs and dairy products consume, on average, less than half the adult Recommended Dietary Allowance of 2.4 mcg of B12.
Some older people are also at high risk for developing B12 deficiency. Up to 30% of people ages 50 and over suffer from atrophic gastritis, a thinning of the stomach lining. This condition reduces the amount of B12 absorbed by the small intestine. Certain other digestive conditions and surgeries also can interfere with B12 absorption.
A deficiency of vitamin B12 may affect balance, memory, and perhaps mood. Therefore it is recommended that risk groups take a multivitamin, eat fortified breakfast cereal, or both.
Source: Harvard Medical School.