Should we be concerned about getting too much vitamin B12?
This is the last 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)
• How Much Vitamin B12 Do We Need Each Day? (https://nutritionfacts.org/video/how-much-vitamin-b12-do-we-need-each-day)
For more on vitamin B12, check out the topic page (https://nutritionfacts.org/topics/vitamin-b12/).
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“Are Large Weekly Doses of Vitamin B12 Safe?” Serious adverse effects,
even with high doses of injected vitamin B12
(hydroxocobalamin), have never been reported. However, some patients
do report acne breakouts after high-dose injections,
which I talked about before. But, hold on. When you look
at the relationship between B12 concentrations
in the blood and mortality, you see graphs like this, where having low levels
isn’t good, with higher mortality, but high levels in the blood
is associated with higher mortality too. What are some of the ways
we could get high B12 levels? One could be
B12 supplementation, but it could also be due to B12
being released from damaged tissues
or not clearing as well from malfunctioning kidneys- in other words,
reverse causation. Instead of high B12
causing disease, disease is causing high B12. How could we tease that out? There is a correlation between
high blood B12 and cancer, for example. Which one might be leading
to the other? Well, when you treat
the cancer, when you shrink the tumors,
B12 levels drop, suggesting that
the active tumor was the source
of high vitamin B12 levels in the circulation
instead of vice versa. And that’s what you see when you look
at other conditions: the blood
B12 concentrations rise as a consequence
of acute and chronic illness. A cause-and-effect relationship between serum
B12 concentrations and subsequent disease
or mortality has never been demonstrated. In fact, how else can you get
lots of B12 in your system? By eating lots of meat. So, high B12 levels
may be a proxy in some cases for increased intake of meat. If you go back
and separate out the effects of different sources of B12, high intake of vitamin B12
in the form of supplements was not associated with any
adverse effect on mortality and, therefore, can be regarded
as safe. And you see the same thing
when you look at the origin of vitamin B12 levels
and mortality across the board in a systematic review
and meta-analysis of all such studies. High blood concentrations
caused by dietary sources of vitamin B12-meat,
eggs, and dairy- may increase
all-cause mortality, but when B12 levels are high
from supplement sources, there doesn’t seem
to be a problem, while higher mortality associated
with cardiovascular disease or obesity is associated
with higher intake of foods like meat. The bottom line
is that long-term studies clearly indicate that treatment with even high
pharmacological doses of B12 and the corresponding increase
in serum B12 levels do not increase mortality risk. “Supplemental forms of B12
are considered safe and there is no evidence-based
Tolerable Upper Intake Level for vitamin B12,” because you just poop out
whatever you don’t absorb. Remember, when you take
a single weekly megadose of 2,000 micrograms of B12, you only absorb
about 20 micrograms of it, and the other 1,980 just get
flushed down the toilet. But wait, before that happens, that massive load of B12
hits our colon. Might that be mucking
with our microbiome? You think we need B12? We only need it
for two enzymes, whereas it’s required
for more than a dozen enzymes in bacteria. Only a minority
of the bacteria in our gut may make it though,
yet the vast majority need it. So, where do they get it? They borrow it from a neighbor, like going next door to get
a cup of flour or something. We may have a thousand or more
difference species in our gut and they share vitamins. It’s like one big open bazaar
down there. This is just to say that B12
is a big deal for bacteria and may play
an unrecognized role in shaping the structure
and function of our microbiome. Okay, but for good or for ill? Vitamin B12 supplements
typically contain doses that far exceed anything we would naturally have seen
evolutionarily and though it’s considered safe, we know our gut bugs are
fighting over it all the time. To what extent might
excessive levels affect us? If mice are given
the human equivalent of just 5,000 micrograms, not much seems to happen
to their microbiomes. But if they’re given
the equivalent of 25,000 micrograms a day, it accelerates the colonization
of a bad bug called Citrobacter rodentium, but as its name suggests,
it’s a mouse-specific pathogen. It’s not a bug
you even see in humans. But what about B12 in people? To date, very few studies
have been done, so the impact of vitamin B12
on our gut microbiome has not been established. And the studies we do have
are all over the place. In this one,
B12 supplementation in an in vitro
colonic stimulation- basically, human feces passed through a series
of beakers and tubes- the B12 seemed to actually have
microbiome benefits. Other similar-type studies
showed that B12 seemed to have
a more limited impact not affecting bacterial growth,
richness, diversity, or total metabolite production. However, there was an increase
in propionate, which is a beneficial
short-chain fatty acid. In this study,
some beneficial bacteria that produce
short-chain fatty acids were reduced by B12,
but overall, the amount of short-chain
fatty acids went up. So, vitamin B12 supplementation may actually be beneficial
for the gut through interactions
with our microbiome. So, while B12 injections are
often used for B12 deficiency, those individuals
may be missing out on microbiome benefits
of oral supplementation. If anything, the potential risk of giving larger weekly doses
versus smaller daily doses would not be
from getting too much, but from getting too little. We’re counting on
that approximate 1% absorption at higher doses, however this passive absorption
may vary between individuals, so if we instead only absorbed
half a percent or a tenth of a percent, we wouldn’t get enough dosing
once a week. To boost absorption,
we can take high doses on an empty stomach. Instead of passively absorbing about 1%
of a 500-microgram dose when taken with a meal,
absorption is boosted by about 60%
on an empty stomach. Although the higher
weekly doses have been proven
to improve B12 status in deficient populations, since we really don’t know
the long-term effects of all that extra B12
hitting our colon, an alternative would be to get 2 or 2.5 micrograms
at each meal, as I talked about
with fortified foods in the last video.
