We finished off our vitamin B12 discussion last time with various dosing strategies,
including the potential of regularly eating fortified foods as a possible means of getting
enough B12.
I mentioned that unlike methylcobalamin, cyanocobalamin is permitted to be used to fortify foods,
and is the form that all the numbers I discussed in that video apply to for supplementation
since it is the best-studied and known to work.
So what's the deal with all these other forms?
Why do they exist at all?
And why do some people recommend against taking cyanocobalamin?
There are two main reasons that people recommend against this form of the vitamin: It's cyanide
content, and the fact that it is not a co-enzyme form of the vitamin and hence is not a so-called
"natural" form.
I'm going to argue why there is no need to be concerned about either of these factors.
If you take methylcobalamin, make sure you watch until the end as I'll also be touching
on how this form of the vitamin may not provide full nutritional adequacy.
First of all, let's take a quick look at how vitamin B12 is actually manufactured to inform
the rest of our discussion.
The cobalamin molecule is far too complex to be synthesised by chemical methods and
all B12 is produced by bacterial metabolism.
This notion of "synthetic" and "natural" B12 is a myth - no B12 is synthetic, it is all
made by micro-organisms.
The four forms of B12 all differ simply by the moiety bonded to the cobalt atom of the
molecule.
Bacteria produce all of adenosyl-, methyl- and hydroxocobalamin, and we intentionally
replace these moieties with a cyano group as part of the extraction process to produce
cyanocobalamin, valued for it's stability and shelf-life in supplements and foods.
But is this added cyano group, a well-known posion, a concern?
The chemically simple cyano group is commonly found in nature including in many foods and
especially certain seeds, so it is unsurprising that we have biological mechanisms to detoxify
small amounts.
Indeed, the moiety is found in various molecules that are important in our own normal functioning.
Like with other chemicals, it is the dose that makes the poison - cyanide only becomes
toxic once these mechanisms are overwhelmed.
So what is the toxic dose of cyanide?
The lowest recorded lethal single dose of cyanide in humans in .56 mg/kg, or around
40 mg or 40000 μg for a 70 kg person.
A common dose of cyanocobalamin is 1000 μg, of which around 2% is cyanide by weight.
So a single dose of this supplement would provide 20 μg cyanide not all of which will
be absorbed, a long way off the worst case scenario lethal dose of 40000 μg.
But we don't take B12 supplements as a one-off, we take them regularly and usually every day.
What about chronic cyanide poisoning?
The WHO has set the provisional maximum tolerable daily intake of cyanide at 20 μg/kg/day,
or around 1400 μg per day for a 70 kg person - still a long way off the 20 μg found in
the supplement.
Of course, I recommend you take a lot less than 1000 μg cyanocobalamin daily, but the
reasons for this have nothing to do with cyanide.
Check out my last video for more on dose.
The other common argument against cyanocobalamin is that it is not a biologically active co-enzyme
form of B12.
However, it is common practice for medicinal preparations, including drugs to be formulated
in an inactive form with the intention of only becoming active on metabolism.
There are many reasons for this depending on the compound, such as improvement of half-life,
taste, sensitivity to stomach acid, sequestration to and use by the relevant tissue, or in the
case of cyanocobalamin, stability and absorbability.
In fact, even methylcobalamin, though marketed as a "biologically active form" that does
not require conversion, is converted into an intermediate before being regenerated to
methylcobalamin and the other vital form for humans - adenosylcobalamin.
This is an important and relatively unknown point - methylcobalamin is only one of the
two essential biologically active forms of the vitamin, and there has even been some
concern that supplementation with only one active form may result in inadequacy of the
other if this regeneration is insufficient.
Given the unjustified condemnation of cyanocobalamin, methylcobalamin has been more heavily promoted
and used recently.
This is not recommended given that we need both forms, so it is suggested we either take
both, or much more simply, just take a cyanocobalamin supplement, which can be converted to both
forms.
The active forms of B12 are not likely to be superior to cyanocobalamin and the only
way we will know for sure is a randomised controlled trial comparing the different forms,
but until we have that there is nothing wrong with taking the cheaper and more reliable
and stable cyanocobalamin and avoiding the higher doses we would need to take to ensure
adequacy with other forms.
To be clear though, the other forms and methods of administration of cobalamin definitely
have their role, such as for pernicious anaemia, tobacco amblyopia, kidney issues and inborn
errors of metabolism including remthylation disorders, as well as cyanide poisoning, amongst
many other indications.
The recommendations in this video are for the general healthy population looking to
maintain an adequate status and you should continue with the form and regimen prescribed
by your health care provider.
In summary, cyanocobalamin is the form used to fortify food.
Like the three other forms of B12, it is made by bacteria but has a cyano group added.
The amount of cyanide it provides is physiologically insignificant.
The fact that it is not a biologically active form may actually be an advantage by being
more easily converted to both active forms.
The other forms play a role in certain conditions, and the bottom line is to follow the regimen
prescribed by your health care provider.
Thanks for watching, and I hope this video has given you a better understanding of the
different forms of B12.
Be sure to share this video with anyone you know that might be uninformed on this topic.
If there was something that wasn't clear from the video, feel free to let me know in the
comments and I'll get back to you.
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That's it for now though guys, talk to ye soon.
Sláinte!