From: altar@beaufort.sfu.ca (Ted Wayn Altar)
Subject: Re: vegan sources: B12, D3 and iron
Organization: Simon Fraser University, Burnaby, B.C., Canada
Date: Tue, 1 Sep 1992 22:27:05 GMT

yn Altar writes:
>>>>It is NOT a good idea to take B12 daily, simply because your
>>>>ability to absorb B12 will decrease with such a surfeit of
>>>>available B12.  The end result is that you simply become overly
>>>>dependent on B12 supplements. Steve Dyer
>>>This is simply not the case.  There is no evidence that taking B12
>>>causes a reduction un the ability to absorb it.
>>
Ted altar
>>The trouble with stating things so emphatically and absolutely is
>>that it would ignore the fact that even experts in this field
>>cannot be so certain that a new paper, or one buried in a less
>>obvious journal, doesn't provide evidence that you do baldly
>>claim simply doesn't exist.  Can you really be so certain of
>>these things?
>>Now, all I have to do is simply cite one reference to refute your
>>categorical statement, fair enough?
>>
>>My reference, which I listed [Hunt & Groff, 1990], states:
>>     "Absorption rate of the vitamin decreases with increased
>>     intake.  At low levels intake, the mean absorption is 70%,
>>     while at very high levels of intake, the absorption rate
>>     drops to 16%" [p. 210]
>
Steve Dyer:
>I can't believe you think this is a refutation.
>
>This is saying that the percentage you absorb is reduced as
>you take more of it.  Nothing particularly surprising here.
>
>However, it says nothing about your ability to absorb the vitamin;
>that is, larger doses do not cause a lowering in B12 absorption
if
>your intake was lowered.
>
>Tell me, Ted: do you understand the difference here?
>Apparently not.
 
 
Ok, no need to be shirky.  We are talking at cross purposes,
and I accept that it is my fault.  Yes, I made a mistake in
using the word "dependant".  See, I can at least admit to
being here wrong.
 
Now, what I meant to say by my poor and inapposite choice of
the word, "dependent", was simply the good point that there
is no advantage to taking daily supplements of B12, that one is
simply not going to store all of the surplus and that one's
former, possibly sufficient reliance of even low amounts of
B12 endogenous in the gut will be changed to a reliance on high
amounts being ingested, with no real benefit.  Of course, if one
stops taking the exogenous high doses of B12, then their will
soon
be a feedback, when serum B12 levels drop to a certain threshold,
to again increase absorption of lower the endogenous and exogenous
amounts.
 
 
Now, as I have already said, I am not against judicious use of B12
supplements but I do think that there is a misunderstanding about
how to go about doing this.  Many people think, or seem to imply by
their advice, that one must take supplements of B12 daily or weekly.
I just tried to provide some information to help specify exactly
how frequently one might take supplements of a certain quantity.
I trust that even you would agree that it is this kind of concrete
information that our questioner was probably hoping to receive in
the first place.
 
 
 
>
>>Also, take a look at:
>>     See K. McMahon (1987). Choline, an essential nutrient? NUTR.
>>     TODAY, 1:95-121.
>
>It's spelled choline.  What's this got to do with B12?
>
Oops, wrong reference here pasted in.  Try:
 
     Victor Herbert (1987).  Recommended dietary intakes (RDI) of
     vitamin B-12 in humans.  Am. J. Clin. Nutr., 45:671-78.
 
 
 
>What makes you think I'm not a vegetarian?
>
Are you?
 
 
 
 
>>Primary hemochromatosis affects about 8/1,000. most of these
>>people having an identifiable genetically transmitted
>>susceptibility.  Not many to be sure but we must remember that
>>this figure only pertains to identified cases.  More would
>>be unidentified (just as we find with diabetes II).  Professor
>>J. Moon at sfu also suspects that even mild overload over many
>>years may be making for some problems in men more frequent than
>>previously suspected.
>
>The rationale for widespread iron supplementation presumably is that
>the public health benefits of such supplementation outweigh the risks
>to a small number of individuals.  Healthy men are in no danger of
>iron overload.
 
Let's not forget what this remark was addressing.  You said that
 
     "There is absolutely no evidence that iron supplementation
     at the levels found in flour is dangerous to men."
 
Now, I pointed out that there is indeed a possible problem for
SOME men.
Of course, we have here the not uncommon dilemma of balancing
between benefiting the many at he cost of a few.  This is
essentially a socio-political decision, a decision that is not
better informed by unguarded remarks like the above.
 
Also, the issue of maintaining present levels iron additives in
foodstuffs is further muddied by the question of "efficacy", as I
earlier mentioned.  There may well be a better solution for
addressing this serious problem of iron anemia that is mainly
prevalent among childbearing women.  For instance, better dietary
habits, individual supplementation for high risk individuals,
supplementation for all woman during periods of greater risk,
better general education on nutrition, greater emphasis in high
school female health classes on iron anemia, etc.  Look, I'm not
against general health measures like fluoride being added to city
water supplies or of their being safe levels of iron being added
to our foodstuffs, but there some responsible health
professionals who are NOT convinced that we should solve the iron
anemia problem simply by further increasing the already possible
current risk to the few.
 
                                                    ted

Newsgroups: rec.food.veg