8 Nov 2005 12:11:22 -0800 in article
<[email hidden]> [email hidden]
Quoted message said:
I eat few animal products and may further reduce my consumption, so I
bought B12 supplements (Country Life brand). Each each tablet provides
over 8,000% of the RDA of B12! This seems like an insane amount,
especially since the body can store B12, so I have the following
questions:
1. The bottle recommends one tablet a day -- are there any problems
with consuming so much B12?
No, B12 is one of the safest vitamins.
Quoted message said:2. Given the body can store B12, can I get by with taking a tablet once
in a blue moon? For instance, with 8,000% and 100% as the RDA, if the
body stores it with 100% efficiency, this means I can take a tablet
once every 80 days. This assumes no issues with absorption and
utilization which may modify this figure (but then, it's 8,333% and I'm
truncating for a fudge factor).
The problem is that quite a many people over 50 - and even some much younger
ones - do develop B12 absorption problem, their intrinsic factor
deteriorates. Often the cause is chronic gastritis. Fortunately from a large
dose of oral B12, humans can absorb about 1% even without intrisinc factor.
Therefore it's possible absorb 10 µg from 1000 µg B12 dose even without
intrinsic factor. So there is a built-in "insurance" or safety factor in a
large dose: it won't harm, but it will guarantee that enough will be
absorbed. More information about this can found in the article
Vitamin B12
Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin
B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline
(1998)
Institute of Medicine (IOM)
<http://books.nap.edu/books/0309065542/html/306.html#pagetop
An introductory article:
Information from your family doctor. Vitamin B12.
Am Fam Physician. 2003 Mar 1;67(5):993-4.
<http://www.aafp.org/afp/20030301/993ph.html>
"What causes problems with absorbing vitamin B12?
Here are some reasons you might have trouble absorbing vitamin B12:
* A disease called pernicious anemia (say this: per-
nish-us ah-nee-mee-ah) could destroy the cells in
your stomach that help you absorb vitamin B12.
* If you use medicine for heartburn and ulcers for a
long time, you may begin to have trouble absorbing
vitamin B12.
* If you have had surgery on your stomach or your
intestines, you may have trouble absorbing vitamin
B12."
About B12 deficiency:
Oh R, Brown DL.
Vitamin B12 deficiency.
Am Fam Physician. 2003 Mar 1;67(5):979-86. Review. Summary for
patients in: Am Fam Physician. 2003 Mar 1;67(5):993-4.
PMID: 12643357 [PubMed - indexed for MEDLINE]
<http://www.aafp.org/afp/20030301/979.html>
"Vitamin B12 (cobalamin) deficiency is a common cause of
macrocytic anemia and has been implicated in a spectrum of
neuropsychiatric disorders. The role of B12 deficiency in
hyperhomocysteinemia and the promotion of atherosclerosis
is only now being explored. Diagnosis of vitamin B12
deficiency is typically based on measurement of serum
vitamin B12 levels; however, about 50 percent of patients
with subclinical disease have normal B12 levels. A more
sensitive method of screening for vitamin B12 deficiency
is measurement of serum methylmalonic acid and
homocysteine levels, which are increased early in vitamin
B12 deficiency. Use of the Schilling test for detection of
pernicious anemia has been supplanted for the most part by
serologic testing for parietal cell and intrinsic factor
antibodies. Contrary to prevailing medical practice,
studies show that supplementation with oral vitamin B12 is
a safe and effective treatment for the B12 deficiency
state. Even when intrinsic factor is not present to aid in
the absorption of vitamin B12 (pernicious anemia) or in
other diseases that affect the usual absorption sites in
the terminal ileum, oral therapy remains effective."
In elderly persons mild B12 deficiency is very common, see
van Asselt DZ, de Groot LC, van Staveren WA, Blom HJ, Wevers RA,
Biemond I, Hoefnagels WH.
Role of cobalamin intake and atrophic gastritis in mild cobalamin
deficiency in older Dutch subjects.
Am J Clin Nutr. 1998 Aug;68(2):328-34.
PMID: 9701190 [PubMed - indexed for MEDLINE]
<URL:http://www.ajcn.org/cgi/reprint/68/2/328>
"... CONCLUSIONS: The high prevalence of mild cobalamin
deficiency in healthy, free-living, older Dutch subjects
could be explained by inadequate cobalamin intake or
severe atrophic gastritis in only 28% of the study
population. Other mechanisms explaining mild cobalamin
deficiency in older people must be sought."
The article
Elia M.
Oral or parenteral therapy for B12 deficiency.
Lancet. 1998 Nov 28;352(9142):1721-2.
<http://www.thelancet.com/journals/lancet/article/PIIS0140673605798214/fulltext>
writes about required oral dose of B12 required in the absence of intrinsic
factor as follows:
"The evidence suggests the following responses to
oral cobalamin without intrinsic factor:4
- 520 µg daily is ineffective;
- 80150 µg daily improves but does not restore circulating
cobalamin or haemoglobin concentrations;
- 100200 µg daily is adequate for most patients;
- 500 µg daily produces satisfactory responses but, because of
individual variability in absorption, some patients have
borderline circulating concentrations;
- 1000 µg daily produces successful long-term results."
The article
Lane LA, Rojas-Fernandez C.
Treatment of vitamin b(12)-deficiency anemia: oral versus parenteral
therapy.
Ann Pharmacother. 2002 Jul-Aug;36(7-8):1268-72. Review.
PMID: 12086562 [PubMed - indexed for MEDLINE]
<http://www.theannals.com/cgi/content/abstract/36/7/1268>
writes also about oral doses needed in B12 deficiency:
"CONCLUSIONS:
Daily oral cyanocobalamin at doses of 1000-2000 microg can
be used for treatment in most cobalamin-deficient patients
who can tolerate oral supplementation. There are
inadequate data at the present time to support the use of
oral cyanocobalamin replacement in patients with severe
neurologic involvement."
--
Matti Narkia
