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What
is it?
Vitamin B12 represents
a family of compounds that contain the mineral cobalt. For this
reason cobalamin is the term used to refer to compounds
having vitamin B12 activity.
Absorption
Absorption of vitamin
B12 occurs in a unique way. Vitamin B12 is released from food
by digestion, especially by stomach acid. The vitamin B12 binds
with intrinsic
factor
which is produced in the stomach. The resulting complex
travels to the last section of the small intestine, called the
ileum. Ileum cells then absorb vitamin B12. Absorption is very
poor unless the intrinsic factor is present.
Functions
- what does it do?
Vitamin B12 is
necesssary for the formation of proteins and red blood
cells, and for the functioning of the nervous system. It participates
in a variety of cellular reactions to release energy from
carbohydrates, fats and protein.
Folate
metabolism. Vitamin
B12 (in coenzyme form) accepts carbon groups from folate as
folate removes it from other compounds. This process regenerates
folate to its active form so that it can continue to remove
carbon groups. Therefore, a vitamin B12 deficiency can contribute
to a deficiency of the active form of folate.
Healthy nervous
system.
Vitamin B12 helps maintain the myelin
sheath
that insulates nerve fibres from each other. People with vitamin
B12 deficiency show irregular destruction of the myelin sheaths,
which eventually causes paralysis and death.
Requirements
- How much do we need?
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|
| |
Recommended
Dietary Allowance*
(µg/day) |
| Life-Stage
(years) |
Males |
Females |
| 0
- 0.5 (0 - 6 months) |
0.4a |
0.4a |
| 0.5
- 1 (7 - 12 months) |
0.5a |
0.5a |
| 1
- 3 |
0.9 |
0.9 |
| 4
- 8 |
1.2 |
1.2 |
| 9
- 13 |
1.8 |
1.8 |
| 14
- 18 |
2.4 |
2.4 |
| Ages
19+ |
2.4 |
2.4 |
| Life-Stage
(years) |
Pregnancy |
Lactation |
| 18
and younger |
2.6 |
2.8 |
| 19
- 30 |
2.6 |
2.8 |
| Ages
31+ |
2.6 |
2.8 |
*The
Recommended Dietary Allowance (RDA) is the average daily
dietary intake level that is sufficient to meet the nutrient
requirements of nearly all (97-98%) healthy individuals
in each life-stage and gender group.
aAdequate Intakes (AI) are used as no RDA
is established. The AI is a recommended
daily intake level based on observed or experimentally determined
approximations of nutrient intake by a group of healthy
people
who are assumed to be maintaining an adequate nutritional
state. |
|
Sources
- Where is it found?
| Vitamin
B12 is produced by bacteria and fungi. |
| Food
Groups |
Food
Sources |
| Nutrient
Density |
| High |
Medium |
Low |
|
| Meat,
poultry, fish, dry beans, eggs, and nuts |
Organ
meats (esp. liver, kidneys, heart), Seafood, Beef, Eggs,
Ham |
| Milk,
yoghurt and cheese |
Milk
and Milk Products |
| |
Generally
not present in plant products |
|
| Those
vegetarians who totally exclude animal products from their
diet need supplemental vitamin B12 to meet their requirements.
|
|
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Deficiency
- When you have too little
Absorption of vitamin
B12 from foods requires the normal function of the stomach,
pancreas, and small intestine. Deficiency may occur as
a result of an inability to absorb vitamin B12 from food. Generally,
most individuals who develop a vitamin B12 deficiency have an
underlying stomach or intestinal disorder that limits the absorption
of vitamin B12.
Characteristic
symptoms
of B12 deficiency include fatigue, weakness, nausea, inflammation
of the tongue, constipation, loss of appetite, and weight loss.
Neurological
changes. Deficiency
can also lead to neurological changes including numbness and
tingling in the hands and feet, difficulty in walking, memory
loss, disorientation, and dementia.
Some of these symptoms
can also result from a other medical conditions besides vitamin
B12 deficiency. It is important to have a physician evaluate
these symptoms so that appropriate medical care can be given.
Pernicious anaemia.
Vitamin
B12 is absorbed in the stomach when it binds to intrinsic factor,
a substance necessary for its absorption. A lack of intrinsic
factor prevents normal absorption of vitamin B12 which results
in the blood disorder called pernicious anaemia.
Anyone with pernicious
anemia usually needs injections of vitamin B12. Pernicious anaemia
is a chronic condition that should be monitored by a physician,
and requires lifelong supplemental vitamin B12.
| Pernicious
anaemia. A
form of anaemia caused by a lack of intrinsic factor, a
substance needed to absorb vitamin B12 (cobalamin) from
the gastrointestinal tract. |
Toxicity
- When you have too much
No toxic or adverse
effects have been associated with large intakes of vitamin B-12
from food or supplements in healthy people.
|
Upper
Limit+
(µg/day) |
| Life-Stage
(years) |
Males |
Females |
| All
ages |
ND |
ND |
| Life-Stage
(years) |
Pregnancy |
Lactation |
| All
ages |
ND |
ND |
| +Upper
Limits (UL) = The maximum level of daily nutrient intake
that is likely to pose no risk of adverse effects. Unless
otherwise specified, the UL represents total intake from
food, water, and supplements.
ND = Not
determinable due to lack of data of adverse effects in
this age group and concern with regard to lack of ability
to handle excess amounts. Source of intake should be from
food only to prevent high levels of intake. |
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