William Wallace: The Sublingual B12 Pitch Is Almost Always Wrong
William Wallace, Co-Founder and Chief Scientific Officer at Supplement Success Solutions, shared a post on LinkedIn:
“The sublingual B12 pitch is almost always wrong.
The mucosa under your tongue has essentially zero capacity to absorb vitamin B12. There are no specialized transporters there.
The tablet dissolves in your mouth, mixes with saliva, gets swallowed, and ends up in your small intestine, which is where it absorbs the same way any oral B12 tablet does.
This matters because there are two real pathways for B12 absorption.
At physiological doses, your stomach releases B12 from food, intrinsic factor binds it, and the IF-cobalamin complex docks at a specific receptor called cubam at the very end of your small intestine. This receptor is saturable.
The literature puts the ceiling around 1.5 to 2 micrograms per meal.
This is the route most physiology textbooks describe and it is the reason classical pernicious anemia (where intrinsic factor is missing or destroyed) was treated for decades with intramuscular injections.
Without intrinsic factor, the receptor route fails.
But there is a second route. Above roughly 500 micrograms, about 1 to 2 percent of any oral dose crosses the entire intestinal mucosa by passive diffusion. Not saturable.
Not receptor-dependent. Not regional.
This is the route that explains why a 1000 to 2000 microgram daily oral tablet works just as well as an injection, even in patients with pernicious anemia.
The 2005 Cochrane systematic review (Vidal-Alaball et al.) reviewed two RCTs and concluded that high-dose oral B12 produced equivalent hematologic and neurologic responses to intramuscular B12.
Two percent of 1000 micrograms is 20 micrograms, well above the daily requirement of 2.4 micrograms.
So where does sublingual fit?
Sharabi et al. (Br J Clin Pharmacol 2003) randomized 30 deficient subjects to 500 mcg sublingual cobalamin, 500 mcg oral cobalamin, or oral B-complex for four weeks.
All three groups corrected. Sublingual produced 288 pmol/L, oral 286 pmol/L, B-complex 293 pmol/L.
There was no significant difference between any of the routes. The sublingual tablet works because it gets swallowed, not because it bypasses the gut.
A larger 2019 retrospective study (Bensky et al., Drug Deliv Transl Res) of 4281 patients went further and found sublingual was at least as good as intramuscular injection for raising serum B12.
Same explanation.
The tablet dissolves, gets swallowed, and the passive diffusion route delivers enough B12 across the entire intestinal surface that the injection route confers no advantage at high doses.
The form and the route get sold; the pharmacology is the same.”
Title: Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency
Authors: Josep Vidal-Alaball, Christopher Butler, Rebecca Cannings-John, Andrew Goringe, Kerry Hood, Andrew McCaddon, Ian McDowell, Alexandra Papaioannou
Title: Comparison of sublingual vs. intramuscular administration of vitamin B12 for the treatment of patients with vitamin B12 deficiency
Authors: Merav Jacobson Bensky, Irit Ayalon-Dangur, Roi Ayalon-Dangur, Eviatar Naamany, Anat Gafter-Gvili, Gideon Koren, Shachaf Shiber
Title: Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral route
Authors: Amir Sharabi, Eytan Cohen, Jaqueline Sulkes, Moshe Garty
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