How are the recommended daily and weekly doses of vitamin B12 derived? Why might we need more than the recommended daily dose for B12?
This is the fourth video in a five-part series on vitamin B12. If you missed any of the previous ones, check out:
• How Long Does It Take to Become Vitamin B12-Deficient and What Are the Symptoms? (https://nutritionfacts.org/video/how-long-does-It-take-to-become-vitamin-b12-deficient-and-what-are-the-symptoms)
• The Best Way to Test for Vitamin B12 Deficiency (https://nutritionfacts.org/video/the-best-way-to-test-for-vitamin-b12-deficiency)
• The Best Source of Vitamin B12: Supplements, Shots, or Fortified Foods? (https://nutritionfacts.org/video/the-best-source-of-vitamin-b12-supplements-shots-or-fortified-foods)
Stay tuned for Are Large Weekly Doses of Vitamin B12 Safe? (https://nutritionfacts.org/video/are-large-weekly-doses-of-vitamin-b12-safe).
For more on vitamin B12, check out the topic page (https://nutritionfacts.org/topics/vitamin-b12/).
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“How Much Vitamin B12 Do We Need Each Day?” There are a couple ways
to derive vitamin B12 recommendations. One is called
the factorial approach, in which the average
requirement of vitamin B12 is calculated as a replacement
of daily losses, adjusted
for dietary bioavailability. So, for example,
if people lose an average of 1 microgram
of B12 a day, and the bioavailability
of tiny amounts of B12 from food is assumed to be about 50%,
if you got 2 micrograms a day, you’d absorb 1 microgram, 50%, and that would replace
the 1 microgram you lose every day. But that’s just
the average daily requirement, based on average daily losses. The average requirement
would mean 50% of people actually need less
and 50% need more. You don’t want
to cover the needs of only half the population,
though, so you add two relative
standard deviations to cover more like 98%
of the population, which just means
you up the average requirement by 20 or 40%. So, if we add 20%
to that 2 micrograms a day we came up with, that comes out to 2.4,
which is, indeed, exactly the RDA for B12
in the United States, and other countries
are similar, recommending 1.5 to 4 micrograms
a day. Another way to derive
B12 recommendations is to see what dose maximizes
B12 function within the body. B12 is used to metabolize MMA
and homocysteine. It looks like
there’s additional benefit up to an intake
of 6 micrograms. So instead of an RDA of 2.4, maybe we should tell people
to get six, since that appears to normalize all the vitamin B12 related
variables. A subsequent, larger study
using the same principle found the same kinds of curves, maximizing B12 functionality
in the same range, suggesting again,
instead of 2.4, maybe we should tell people to get somewhere
between 4 and 7. Since the bioavailability
of tiny amounts in the diet is assumed to be
around 50 percent, that would mean
we should shoot for absorbing
2 to 3.5 micrograms into our body every day. The bioavailability
of larger amounts found in supplements
is different, though, based on the famous
Heinrich equation. Down at 1 or 2 micrograms,
B12 absorption is about 50%, but as you can see,
only about 1% of a 2,000-microgram dose
is absorbed. Okay, so if we want
to absorb 2 to 3.5 a day through fortified foods
or supplements, what do we do? Well, if we ate B12-fortified
foods at every meal, three times a day, how much would we have to get
at each meal? If each meal had 2 micrograms, then we would absorb
throughout the day 0.9 times 3, or 2.7, which would be
in the 2 to 3.5 range we’re shooting for. So, if you had even like
three quarters of a cup (180 ml) of soymilk at breakfast and then sprinkled on
as little as one teaspoon of certain brands
of nutritional yeast on your lunch and dinner,
you’d be all set. Instead, if you were going
to take supplements, how much would you
have to take each week to absorb 2 to 3.5 micrograms’
worth a day? Well, if you took 2,000
once a week, that would get you 19.5, which would average out
to about 2.8 a day. If you’d rather take
a supplement once a day instead of once a week,
50 microgram tablets are most frequently advised
and used. In theory, 50 micrograms
would get you 1.9, and, in practice,
it looks like 50 does get you that 2 micrograms. And, indeed, in a comparison of chewable 50-microgram
daily doses to 2,000 once-a-week doses
in vegans and vegetarians with marginal deficiency, they both worked just as well
in bringing down MMA and homocysteine levels. One option for fortified foods that have enough for once-a-day
dosing is LeafSide, just-add-water whole food,
plant-based meals that have 75 micrograms
of B12 per serving. Please note that neither I
nor Nutrition Facts have ever and will ever accept
any money to promote
any for-profit product. So, unlike almost anywhere
on the internet, you know that
when I plug a product it’s strictly
because I believe in it and think
it’s going to help people, not because it’s lining
my pockets.
