How much B could B12 be, if B12 could be 12?

Dear Doctor Ninja,

I recently had my annual physical where I told my physician about my endless battle with canker sores. To figure out what was going on we did some basic blood work and found out that I have a deficiency in Vitamin B12.

I’ve been taking over the counter B12 supplements for about 6 weeks now, but my canker sores are still just as prevalent as before. My question is really a few questions. How long does it take for oral, over the counter supplements to kick in to fix this kind of issue? Would the B12 shots be a better option for this? And finally, do supplements really fix this kind of issue to begin with, or is it just a way to cover up some low blood test results?


Cankered Out

There is one trial examining how effective vitamin B12 is at reducing both how long canker sores last as well as how often people get them. This study showed a dramatic reduction in both how long sores lasted as well as the number of sores per month, with an average starting rate of 27.6 sores per month down to 3.9 sores per month. In this study, the participants took 1000mcg of vitamin B12 every day before going to bed.

There was another study looking at whether a multivitamin would do the same thing, and showed that it didn’t, but the dose of vitamin B12 was at the recommended daily allowance level, which is about 2.4mcg.

Since it seems the lowest dose of vitamin B12 commonly sold is 1000mcg though, getting the dose doesn’t seem to be a problem.

The positive study looked at sores every month. The first major drop in the number of sores per month happened at the 2-month mark, with another major drop at the 5-6 month mark.

Participants who were taking the placebo also noticed a drop in the number of sores per month, which was similar to the B12 group at the 3-4 month mark, but nowhere near the B12 group at the 5-6 month mark.

Whether or not a B12 shot would be “better” would depend entirely on whether a shot would keep your levels of B12 high enough between injections comparable to taking 1000mcg in a pill or tablet. But injections haven’t been studied specifically for canker sores.

One thing to note is that people who had underlying diseases that are associated with canker sores (Behcet disease, rheumatoid arthritis, and lupus, for example) were not studied; so if you fall into any of these categories, these results would not apply.

People who had an existing B12 deficiency were also not studied, so in your case, WHY you were B12 deficient becomes an important aspect of whether or not this research would apply specifically to you. If you were deficient for purely dietary reasons, then adjusting your diet to be not-deficient and then supplementing ON TOP of that, would put you more into the category of the studied participants. However, if you were/are deficient for other reasons (e.g. an absorption problem), then addressing that particular issue might be necessary.

But even if you don’t fit strictly into the category, the question for most people in your circumstance might look more like this:

“If I take 1000mcg of vitamin B12 every day, could it hurt me?”

And the answer to that question is almost certainly, “No,” from a physical point of view. Financially, vitamin B12 is quite cheap, but I don’t know how strapped you are for cash. And then there’s the “mental” cost of remembering to take it every night (which you could do by putting it next to your toothbrush, if you brush your teeth every night).

The costs of taking vitamin B12 every night for 6 months appear pretty low, for a potential dramatic fix.

If you’re looking to really give this a shot, you would want to make sure that you’re getting 1000mcg per day; and probably stick to it for 6 months before deciding it’s not working.

The other question you might ask yourself is:

“If this works, am I prepared to take vitamin B12 every night possibly indefinitely?”

And that’s an answer only you know, depending on how annoying your canker sores are and whether you’re willing to pay the price to control them (if the B12 solution works).

The good news is that you have an end date to decide whether or not to stop. If there’s no real change within 6 months, then your results would be outside what we would expect to see. I wouldn’t waste any more time or money at that point and definitely wouldn’t pile another thing on top of it to see if they “work together” which can be a common trap people fall into for fear that they’re missing a critical component in a mix of solutions. In this case, the timeline is pretty clear.

Reference: Volkov I, Rudoy I, Freud T et al. Effectiveness of Vitamin B12 in Treating Recurrent Aphthous Stomatitis: A Randomized, Double-Blind, Placebo-Controlled Trial, J Am Board Fam Med January 2009, 22 (1) 9–16; DOI:

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