B12

Part of Vitamin B Complex.

Function

Formation of red blood cells, brain, nervous system, synthesis of DNA, fat/carb metabolism

Vitamin deficiency

Poor growth, inflamed tongue, anemia, sluggish metabolism, nervousness

Vitamin B-12 comes only from animal foods. Most strict, long-term vegetarians are vitamin B12 deficient and must therefore supplement B-12.

Many elderly people are also deficient because their production of the intrinsic factor needed to absorb the vitamin from the small intestine decline rapidly with age. When deficiency occurs, it is more commonly linked to a failure to effectively absorb B12 from the intestine rather than a dietary deficiency. Absorption of B12 requires the secretion from the cells lining the stomach of a glycoprotein, known as intrinsic factor. The B12-intrinsic factor complex is then absorbed in the ileum (part of the small intestine) in the presence of calcium.

B12 deficiency can also be found in those with a neurological dysfunction that is almost indistinguishable from senile dementia and Alzheimer’s disease, asthma, depression, AIDS, multiple sclerosis, tinnitus, diabetic neuropathy and low sperm counts.

Food sources

Poultry, liver, milk, shellfish, beef, egg yolk, crab, sardine, salmon, herring, oyster

Vegetables and fruits are very poor sources. No plant foods can be relied on as a safe source of vitamin B12.

Examples of therapeutic usage (not always proven effective or safe)

Certain people are unable to produce intrinsic factor and the subsequent pernicious anemia is treated with injections of B12. 2000 microgram/day for one month is recommended followed by 1000 microgram/day. Some physicians still maintain that monthly injections of vitamin B12 is required to maintain adequate levels in the elderly and in patients with a diagnosed deficiency.

Toxic dose – symptoms

B12 has very low toxicity and high intakes are not thought to be dangerous but caution may be warranted.

AIs (Adequate Intakes)

Infants 0-6 months 7-12 months

Micrograms per Day 0.4 0.5

RDAs (Recommended Dietary Allowances)

People older than 50 years should meet their RDA by consuming mainly  foods fortified with vitamin B12, because 10-30% of these people malabsorb foodbound vitamin B12.

Children 1-3 years 4-8 years	- 0.9 1.2
Males 9-13 years 14-18 years 19-30 years 31-50 years 50-70 years > 70 years	- 1.8 2.4 2.4 2.4 2.4 2.4
Females 9-13 years 14-18 years 19-30 years 31-50 years 50-70 years > 70 years	- 1.8 2.4 2.4 2.4 2.4 2.4
Pregnancy < 19 years 19-30 years 31-50 years	- 2.6 2.6 2.6
Lactation < 19 years 19-30 years 31-50 years	- 2.8 2.8 2.8

Source: USDA Dietary Reference Intakes