Extraordinarily small amounts of vitamin B
suffice for daily nutritional needs. The official US and Canadian recommendations for daily intake are as follows:
- 0-6 months: 0.4 mcg
- 7-12 months: 0.5 mcg
- 1-3 years: 0.9 mcg
- 4-8 years: 1.2 mcg
- 9-13 years: 1.8 mcg
Males and Females
- 14 years and older: 2.4 mcg
is available in three forms: cyanocobalamin, hydrocobalamin, and methylcobalamin. The first is the most widely available and least expensive, but some experts think that the other two forms are preferable.
is found in most animal foods; it is also found
in animal food (unless otherwise fortified).
Clams and beef liver have extremely high amounts of this vitamin. The National Institutes of Health's Office of Dietary Supplements offers this list of foods that are high in B12:72
Vitamin B12 content
||% Daily Value
|Beef liver, cooked
|100% fortified cereal
|Rainbow trout, cooked
|Light tuna, canned in water
|Cheeseburger and bun
|25% fortified cereal
|Top sirloin beef
|Low-fat fruit yogurt
|Cured ham, roasted
|Hard boiled egg
|Chicken breast, roasted
Vitamin B12 Deficiency
deficiency is rare in the young, but it is not unusual in older people: Probably 10% to 20% of the elderly are deficient in B
This may be because older people have lower levels of stomach acid. The vitamin B
in our food comes attached to proteins and must be released by acid in the stomach in order to be absorbed. When stomach acid levels are low, we do not absorb as much vitamin B
from our food. Fortunately, vitamin B
supplements do not need acid for absorption and should, therefore, get around this problem. However, for reasons that are unclear, one study found that B
-deficient seniors need very high dosages of the supplements to normalize their levels, as high as 600 to 1,000 mcg daily.
Similarly, people who take medications that greatly reduce stomach acid, such as
(Zantac) also may have trouble absorbing B
from food and could benefit from supplementation.
Stomach surgery and other conditions affecting the digestive tract can also lead to B
deficiency. Vitamin B
absorption or levels in the blood may also be impaired by
metformin and phenformin
(for diabetes), and
Exposure to nitrous oxide (such as may be experienced by dentists and dental hygienists) might cause B
deficiency, but studies disagree.
Slow-release potassium supplements might impair B
absorption as well.
deficiency can cause anemia and, potentially, nerve damage. The latter may become permanent if the deficiency is not corrected in time. Anemia most often develops first, leading to treatment before permanent nerve damage develops. However, folate supplements can get in the way of this "early warning system." This is why people are cautioned against taking high doses of folate without medical supervision. When taken at a dosage higher than 400 mcg daily, folate can prevent anemia caused by B
deficiency, thereby allowing permanent nerve damage to develop without any warning. More mild deficiencies of vitamin B
may cause elevated levels of homocysteine in the blood, potentially increasing risk of heart disease. (See the
article for more information.) Mild B
deficiency (too slight to cause anemia) may also impair brain function.
: Total vegetarians (vegans) must take vitamin B
supplements or consume B
-fortified foods, or they will eventually become deficient.
Contrary to some reports, seaweed and tempeh do
. (Some forms of blue-green algae, such as
, but it is not in an absorbable state.
It appears that individuals who take medications that dramatically lower stomach acid, such as
proton pump inhibitors
, would benefit by taking B
Other individuals likely to be deficient in B
, such as the elderly, or those taking the medications listed in Requirements/Sources, might well benefit from a daily B
supplement to prevent B
For pernicious anemia, B
injections are traditionally used but research has shown that oral B
works just as well, provided you take enough of it (between 300 and 1,000 mcg daily).
Weak evidence suggests that B
supplements may improve sperm activity and sperm count; on this basis, they could be useful for
Some cases of
might be due to vitamin B
One placebo-controlled, double-blind study, enrolling 49 people with eczema, found benefit with a cream containing vitamin B
at a concentration of 0.07%.
is hypothesized to work for eczema by reducing local levels of the substance nitric oxide (not related to nitrous oxide).
On the basis of weak and sometimes contradictory evidence, vitamin B
has been suggested for
33-37amyotrophic lateral sclerosis
38carpal tunnel syndrome
39,40multiple sclerosis (MS)
41-45restless legs syndrome
Some evidence suggests that people with
(splotchy loss of skin pigmentation) might be deficient in vitamin B
and supplementation along with folate may be helpful.
However, the evidence is very weak and not all studies agree.
Some alternative practitioners recommend the use of injected vitamin B
. However, the only scientific support for this approach comes from one study that was not double-blind.
(For information on the importance of a double-blind design, see
Why Does This Database Rely on Double-blind Studies?
is also sometimes recommended for numerous other problems, including
. But, there is not a lot of evidence as yet that it really works.
A double-blind trial of vitamin B
for seasonal affective disorder (SAD—a type of
related to lack of light during the winter) failed to find evidence of benefit.
And, a randomized trial involving older adults with mild depression found that taking
(400 mcg) and vitamin B
(100 mcg) daily for two years was no better than a placebo for reducing depressive symptoms.
One double-blind, placebo-controlled study of 140 people with mildly low B
levels failed to find the supplement
helpful for improving mental function and mood.
Another study failed to find evidence that vitamin B
improved general sense of
among seniors with signs of mild B
Although vitamin B
has been proposed as a treatment for
, this recommendation is based solely on the results of one small, poorly designed study.
More recent and better-designed studies found little to no benefit.