Sublingual B12 no better than just swallowing
Question (edited for clarity):
It is always explicitly recommended that Vitamin B12 tablets should be dissolved under the tongue (aka “sublingual”). I wonder if that is also true for other minerals and vitamins of special concern to vegetarians, such as iron and vitamin D2? If not, why is this the case with vitamin B12?
I have always told people who asked about sublingual B12 that there was no evidence, of which I was aware, that sublingual was any better than just chewing. Despite this, until today, I had been recommending sublingual in my Step 1 Recommendations, which are geared towards people who have not recently had a reliable source of B12. I have recommended sublingual as a precaution just in case it was more effective. In recent years, I have been more diligent about trying not to recommend anything just to be prudent unless specifically stating that is why I am recommending it. This suggestion for sublingual (versus just oral) was a remnant left over from previous times.
Still, I did not know whether sublingual was better than oral until I got this question and decided to check in on the research. As it turned out, there was a study as long ago as 2003. Yikes! I guess I hadn’t checked in quite a long time.
The 2003 study compared 500 µg per day via the sublingual and oral routes. The results were that sublingual was absolutely no better than oral B12 at raising vitamin B12 levels or improving B12 activity (as measured by homocysteine and methylmalonic acid levels). The report did not specifically state whether the tablets were chewed or not (I assume that they were swallowed whole). So now I’m not sure I should even suggest that the tablets be chewed, but because other studies have shown a benefit to chewing, I will leave that in my recommendations.
As for other vitamins and minerals, I have never checked into the research on taking them via the sublingual route, but my sense is that there would not be any benefit. It might even be dangerous to try this with iron given that it is a pro-oxidant and probably should not be held in constant contact with your tissues.
Sharabi A, Cohen E, Sulkes J, Garty M. Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral route. Br J Clin Pharmacol. 2003 Dec;56(6):635-8. | link