Re: Vitamin B12
- From: rpautrey2 <rpautrey2@xxxxxxxxx>
- Date: Tue, 25 Dec 2007 19:44:32 -0800 (PST)
Vitamin B12
What high-vitamin B12 foods can do for you:
support production of red blood cells and prevent anemia
allow nerve cells to develop properly
help your cells metabolize protein, carbohydrate, and fat
What events can indicate a need for more high-vitamin B12 foods?
red or sore tongue
tingling or numbness in feet
nervousness
heart palpitations
depression
memory problems
Excellent sources of vitamin B12 include calf's liver and snapper.
Description
Function
Deficiency Symptoms
Toxicity Symptoms
Cooking, storage and processing
Factors that affect function
Drug-nutrient interaction
Nutrient interaction
Health conditions
Supplements
Food Sources
Public Recommendations
References
Description
What is vitamin B12?
Vitamin B12 is one of the most controversial members of the vitamin
family collectively referred to as the "B-complex" vitamins. Although
the full chemical structure of B12 was not identified until the 1960s,
two Nobel Prizes have already been awarded for research involving this
vitamin. The first of these Nobel Prizes, awarded in 1934, involved
the discovery that a food (liver, a very rich source of B12) could be
used to treat a particular type of anemia (inability of the
bloodstream to carry oxygen) called pernicious anemia. The second came
thirty years later when chemists figured out the exact structure of
this important vitamin.
Vitamin B12 is unusual with respect to its origins. While most
vitamins can be made by a wide variety of plants and specific animals,
no plant or animal has been shown capable of producing B12, and the
exclusive source of this vitamin appears to be tiny microorganisms
like bacteria, yeasts, molds, and algae.
Like most vitamins, B12 can occur in a variety of forms and can take
on a variety of names. Names for B12 include: cobrynamide, cobinamide,
cobamide, cobalamin, hydroxcobalamin, aquocobalamin, nitrotocobalamin,
and cyanocobalamin. Each of these designations contains a form of the
word "cobalt," since cobalt is the mineral found in the center of the
vitamin.
B-12 is also unusual in that it is dependent upon a second substance,
called intrinsic factor, to make its way from the "GI" tract
(gastrointestinal tract--the stomach and intestines) into the rest of
the body. Without intrinsic factor, which is a unique protein made in
the stomach, vitamin B12 cannot gain access to the rest of the body
where it is needed.
How it Functions
What is the function of vitamin B12?
Forming red blood cells
Perhaps the most well-known function of B12 involves its role in the
development of red blood cells. As red blood cells mature, they
require information provided by molecules of DNA. (DNA, or deoxyribose
nucleic acid, is the substance in the nucleus of our cells which
contains genetic information.) Without B12, synthesis of DNA becomes
defective, and so does the information needed for red blood cell
formation. The cells become oversized and poorly shaped, and begin to
function ineffectively, a condition called pernicious anemia. More
often than not, pernicious anemia isn't caused by a lack of B12
itself, but by a lack of intrinsic factor -- the stomach-made protein
required for the absorption of B12.
Developing nerve cells
A second major function of B12, less clearly understood than the
first, involves its participation in the development of nerve cells. A
coating which encloses the nerves -- called the myelin sheath -- forms
less successfully whenever B12 is deficient. Although the vitamin
plays an indirect role in this process, supplementation of B12 has
been shown to be effective in relieving pain and other symptoms in a
variety of nervous system disorders.
Other roles for vitamin B12
Protein -- the component of food required for growth and repair of
cells -- depends upon B12 for proper cycling through the body. Many of
protein's key components, called amino acids, become unavailable for
use in the absence of B12. Since one of the steps in carbohydrate and
fat processing requires B12 for its completion, insufficiency of the
vitamin can also affect the movement of carbohydrates and fats through
the body.
Deficiency Symptoms
What are deficiency symptoms for vitamin B12?
Although B12 is not the only nutrient deficiency that can contribute
to occurrence of the following symptoms, B12 deficiency should be
considered as a possible underlying factor whenever any of the
symptoms listed below are present.
Symptoms potentially associated with vitamin B12 deficiency:
dandruff nervousness
decreased blood clotting numbness in feet
decreased reflexes paleness
depression red tongue
difficulty swallowing sore tongue
fatigue tingling in feet
heart palpitations weakness
memory problems weak pulse
menstrual problems
Toxicity Symptoms
What are toxicity symptoms for vitamin B12?
No toxicity levels have been reported for vitamin B12, and no toxicity
symptoms have been identified in scientific research studies. Even
long-term studies, in which subjects have taken 1,000 micrograms of
the vitamin on a daily basis for five years, have revealed no toxicity
effects.
When the National Academy of Sciences established its current
Tolerable Upper Intake Levels (ULs) for the B complex vitamins in
1998, it did not establish a Tolerable Upper level for vitamin B12.
While not a consideration in the daily diet or in everyday
supplementation of B12, it should be noted that in the case of some
medical therapies involving injection of B12, allergic reactions have
been reported.
Impact of Cooking, Storage and Processing
How do cooking, storage, or processing affect vitamin B12?
When derived from animal foods, vitamin B12 is fairly well preserved
under most cooking conditions. For example, about 70% of the vitamin
B12 present in beef is retained after broiling for 45 minutes at 350º
Fahrenheit. Similarly, about 70% of B12 is still present after cow's
milk is boiled for 2-5 minutes. Retention of vitamin B12 in plant-
based foods like tempeh, a fermented food made from soy, has not been
well researched.
Factors that Affect Function
What factors might contribute to a deficiency of B12?
B-12 and the stomach
Stomach problems can contribute to a B12 deficiency in two ways.
First, irritation and inflammation of the stomach can prevent the
stomach cells from functioning properly. When functioning improperly,
the cells may stop producing a substance required for B12 absorption
called intrinsic factor (IF). Without IF, B12 cannot be absorbed from
the gastrointestinal tract into the body's cells.
A second way for stomach problems to create B12 deficiency is through
inadequate secretion of stomach acids. Lack of stomach acids (a
condition called called hypochlorhydria) gets in the way of B12
absorption since most B12 in food is attached to proteins in the food,
and stomach acids are necessary to release the B12 from these
proteins.
The above stomach problems that can contribute to B12 deficiency have
a wide variety of causes. These causes include abuse of over-the-
counter antacids, abuse of prescription medicines used to control
stomach acidity, and stomach ulcers (also called gastric ulcers),
which may themselves be due to infection with the bacteria,
helicobacter pylori.
B12 and vegetarianism
The ability of a strict vegetarian diet to supply adequate amounts of
B12 remains controversial, despite increasing evidence in support of
vegetarianism and its nutritional adequacy. The controversy is fueled
by two somewhat divergent schools of thought. One school emphasizes
the fact that most animals, including humans, are capable of storing
long-term supplies of B12.
In humans, these stores may last for twenty years or longer. Given
this potential for storage, a daily requirement for B12 is regarded as
highly unlikely.
A second school of thought, however, points to the unreliability of
plants as sources of B12. For strict vegetarians who eat no animal
products whatsoever, this unreliability may pose a problem. Since no
plant is capable of making B-12, the amount of B12 in plant food
depends upon the relationship of the plant to soil and root-level
microorganisms (bacteria, yeasts, molds, and fungi) which make the
vitamin. Cultured and fermented bean products like tofu, tempeh, miso,
tamari and shoyu may or may not contain significant amounts of B12,
depending upon the bacteria, molds, and fungi used to produce them.
The B12 content of sea vegetables also varies according to the
distribution of microorganisms in the surrounding sea environment.
Unfortunately, reliable nutrient analyses are often unavailable for
consumers of these products, and labeling for B12 content is not
required. In general, tofus, tempehs, and sea vegetables tend to be
more consistent sources of B12 than misos, tamaris, and shoyus.
Depending upon the medium in which they are grown, brewer's and
nutritional yeast can also be significant sources of B12 in a strict
vegetarian diet.
Drug-Nutrient Interactions
What medications affect vitamin B12?
Categories of drugs that can diminish the body's supply of vitamin B12
include antibiotics, anticancer medications, anticonvulsants, anti-
gout medications, antihypertensives, antiParkinson's medications,
antipsychotics, antituberculosis medications, birth control pills,
cholesterol-lowering drugs, and potassium replacements. Examples of
specific medications in each category are listed below.
CATEGORY NAME OF MEDICATION
Antibiotics Kantrex (kanamycin)Neomycin
Anticancer Drugs Methotrexate
Anticonvulsants Dilantin (phenytoin)Mysoline (primidone)Phenobarbitol
Antigout Drugs Colbenamid (colchicine)Colchicine
Antihypertensives Aldomet (methyldopa)
AntiParkinson's Larodopa (levodopa)
Antipsychotics Thorazine (chlorpromazine)
AntituberculosisDrugs INH (isoniazid)
Birth ControlPills Ovulen (ethynodiol diacetate)Ovral (ethinyl
estradiol)Ortho-Novum (norethindrone ethinyl estradiol)
Cholesterol-LoweringDrugs CholestyramineAtromid (clofibrate)
PotassiumReplacements K-Lor (potassium chloride)Micro-KSlow-K
Nutrient Interactions
How do other nutrients interact with vitamin B12?
Vitamin B6 is required for proper absorption of vitamin B12, and
deficiency of vitamin B6 has been shown to impair B12 absorption in
animal studies.
Conversion of vitamin B12 from its non-active into its biologically
active form requires the presence of vitamin E. Individuals at risk
for vitamin E deficiency may show signs of vitamin B12 deficiency as
well.
Contrary to research from the mid 1970s, supplemental doses of vitamin
C above the 500 milligram level do not appear to compromise B12
function.
Excessive intake of folic acid can mask B-12 deficiencies, and
individuals at risk for vitamin B12 deficiency who are also taking
folic acid in supplement form should consult with their healthcare
practitioner.
Health Conditions
What health conditions require special emphasis on vitamin B12?
Vitamin B12 may help in the prevention and/or treatment of the
following health conditions:
Alcoholism
Anemia (Pernicious)
Arthritis (Rheumatoid)
Asthma (Bronchial)
Atherosclerosis
Cancer
Celiac Disease
Crohn's Disease
Dermatitis (Seborrheic)
Epstein-Barr Virus
Fatigue
Leukemia
Lupus
Multiple Sclerosis
Neuropathies/Neuromuscular degeneration
Form in Dietary Supplements
What forms of vitamin B12 are found in dietary supplements?
Cyanocobalamin is the form of B12 most commonly found in vitamin
supplements. However, this form of the vitamin is only found in the
laboratory, where a cyanide molecule is added to the vitamin to help
stabilize it in tablet or capsule form. Once inside of the body, the
cyanide portion is broken off and the vitamin is activated. While no
suggestion has been made as to increased risk
of cyanide poisoning through the use of B12 in this form, some
healthcare professionals prefer the hydroxycobalamin or dibencozide
forms of the vitamin which do not contain the cyanide molecule and are
naturally-occurring.
Since the cobalamin forms of the vitamin are the only ones known with
certainty to play an active role in the body, alternative forms of B12
like cobamamide may be less preferable for supplementation.
On a drop-for-drop basis, sublingual (under-the-tongue) forms of B12
deliver more of the vitamin into your bloodstream than tablet or
intranasal (inhaled through the nose) versions.
Food Sources
Introduction to Nutrient Rating System Chart
The following chart shows the World's Healthiest Foods that are either
excellent, very good or good sources of this nutrient. Next to each
food name you will find the following information: the serving size of
the food; the number of calories in one serving; DV% (percent daily
value) of the nutrient contained in one serving (similar to other
information presented in the website, this DV is calculated for 25-50
year old healthy woman); the nutrient density rating; and the food's
World's Healthiest Foods Rating. Underneath the chart is a table that
summarizes how the ratings were devised. Read detailed information on
our Nutrient Rating System.
Introduction to Nutrient Rating System Chart
In order to better help you identify foods that feature a high
concentration of nutrients for the calories they contain, we created a
Food Rating System. This system allows us to highlight the foods that
are especially rich in particular nutrients. The following chart shows
the World's Healthiest Foods that are either an excellent, very good,
or good source of vitamin B12 (cobalamin). Next to each food name,
you'll find the serving size we used to calculate the food's nutrient
composition, the calories contained in the serving, the amount of
vitamin B12 (cobalamin) contained in one serving size of the food, the
percent Daily Value (DV%) that this amount represents, the nutrient
density that we calculated for this food and nutrient, and the rating
we established in our rating system. For most of our nutrient ratings,
we adopted the government standards for food labeling that are found
in the U.S. Food and Drug Administration's "Reference Values for
Nutrition Labeling." Read more background information and details of
our rating system.
World's Healthiest Foods ranked as quality sources of:
vitamin B12 (cobalamin)
Food Serving
Size Cals Amount
(mcg) DV
(%) Nutrient
Density World's
Healthiest
Foods Rating
Calf's liver, braised 4 oz-wt 187.1 41.39 689.8 66.4 excellent
Snapper, baked/broiled 4 oz-wt 145.2 3.97 66.2 8.2 excellent
Venison 4 oz-wt 179.2 3.60 60.0 6.0 very good
Shrimp, steamed/boiled 4 oz-wt 112.3 1.69 28.2 4.5 very good
Scallops, baked/broiled 4 oz-wt 151.7 2.00 33.3 4.0 very good
Salmon, chinook, baked/broiled 4 oz-wt 261.9 3.25 54.2 3.7 very good
Beef tenderloin, lean, broiled 4 oz-wt 240.4 2.92 48.7 3.6 very good
Lamb loin, roasted 4 oz-wt 229.1 2.45 40.8 3.2 good
Cod, baked/broiled 4 oz-wt 119.1 1.18 19.7 3.0 good
Halibut, baked/broiled 4 oz-wt 158.8 1.55 25.8 2.9 good
Yogurt, low-fat 1 cup 155.1 1.38 23.0 2.7 good
Cow's milk, 2% 1 cup 121.2 0.89 14.8 2.2 good
Egg, whole, boiled 1 each 68.2 0.49 8.2 2.2 good
World's Healthiest
Foods Rating Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%
Public Health Recommendations
What are current public health recommendations for vitamin B12?
The most recent Recommended Dietary Allowances (RDAs) for vitamin B12
were set in 1998 by the National Academy of Sciences. The RDAs were
established for all persons 1 year of age and older. For infants under
the age of 1 year, Adequate Intake (AI) levels were set. These AI and
RDA guidelines are as follows:
0-6 months: 400 nanograms
6-12 months: 500 nanograms
1-3 years: 900 nanograms
4-8 years: 1.2 micrograms
males 9-13 years: 1.8 micrograms
males 14 years and older: 2.4 micrograms
females 9-13 years: 1.8 micrograms
females 14 years and older: 2.4 micrograms
Pregnant females of any age: 2.6 micrograms
Lactating females of any age: 2.8 micrograms
References
Areekul S, Pattanamatum S, et al. The source and content of vitamin
B12 in the tempehs. J Med Assoc Thai 1990 Mar 73(3):152-156 1990.
Carmel R. Cobalamin, the stomach, and aging. Am J Clin Nutr 1997 Oct
66(4):750-759 1997.
Clementz GL, Schade SG. The spectrum of vitamin B12 deficiency. Am Fam
Physician, 1990 Jan 41(1):150-162 1990.
Davis, RE. Clinical chemistry of vitamin B12. Adv Clin Chem 1984
24:163-216.
Delpre G, Stark P, and Niv Y. Sublingual therapy for cobalamin
deficiency as an alternative to oral and parenteral cobalamin
supplementation. Lancet 1999 Aug 28 354(9180):740-741 1999.
Fennema OR (Ed.). Food chemistry. Second edition. Marcel Dekker, New
York, 1985 1985.
Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human
Metabolism. West Publishing Company, New York, 1995.
Herbert V, Jacob E, Wong K-T, et al. Destruction of vitamin B12 by
vitamin C (letter). Am J Clin Nutr 30:297.
Lovblad K, Ramelli G, et al. Retardation of myelination due to dietary
vitamin B12 deficiency: cranial MRI findings. Pediatr Radiol 1997 Feb
27(2):155-158 1997.
Machlin LJ and Langseth L. 1988. Vitamin-vitamin interactions. In:
Bodwell CE and Erdman JW (Eds). Nutrient interactions. Marcel Dekker,
New York, p297.
Machlin LJ and Langseth L. 1988. Vitamin-vitamin interactions. In:
Bodwell CE and Erdman JW (Eds). Nutrient interactions. Marcel Dekker,
New York, p296.
Machlin LJ and Langseth L. 1988. Vitamin-vitamin interactions. In:
Bodwell CE and Erdman JW (Eds). Nutrient interactions. Marcel Dekker,
New York, p301.
Plaut GW, Smith CM, Alworth WL. Biosynthesis of water-soluble
vitamins. Ann Rev Biochem 1974 43:899-922 1974.
Spalla C, Grein A, et al. Microbial production of vitamin B12. 1997,
Chapter 15 in: Bickel H and Schultz Y (Eds), Digestion and absorption
of nutrients, Int J Vit and Nutr Res, Sup 25, Hans Huber Pub, Bern,
pp257-284 1997.
Sutterlin MW, Bussen SS, Rieger L et al. Serum folate and Vitamin B12
levels in women using modern oral contraceptives (OC) containing 20
microg ethinyl estradiol. Eur J Obstet Gynecol Reprod Biol 2003 Mar
26;107(1):57-61 2003.
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