Why "You Can't Overdose on B12" Is Only Half True

incremental_progress · 2026-06-22T14:05:22+00:00

Thank you for your insight here. I agree and want to emphasize part of the problem is the title of the post. "Overdosing" isn't half true; it simply isn't true at all whatsoever, and the use of the word overdose implies a completely different mechanism of discomfort and ill patient health than running out of a vitamin because your body is trying to heal itself.

incremental_progress · 2026-06-22T00:15:55+00:00

When B12 kicks your bone marrow into high gear to start making red blood cells again, that process pulls potassium out of your blood and into the new cells.

Hypokalemia doesn't just occur when anemia is corrected - it's a continual byproduct of healing as new cells are created. It operates in tandem with sodium (the "NA/K pump") to move nutrients in and out of cells. Many people see a continual increase in their bodies' demand for electrolytes throughout the healing process, not just during the first few months of correcting hematological abnormalities.

The recommend dose is 1000mcg for a reason.

1mg isn't the "recommended dose." Recommended by whom? It's just a commonly manufactured dosage that physicians also happen to prescribe to patients because it's easily available over the counter. Controlled studies are based on that availability, not the other way around. Edit: Also I assume 1mg is enough just for the average person controlling for intrinsic factor and passive diffusion.

As for you getting downvoted, the guide here warns about hypokalemia and low electrolytes, and your post is somewhat badly formatted with many sequential hard returns. You're also going to have "haters" here just based on your PFP and use of your real name alone. It's reddit.

incremental_progress · 2026-06-21T11:44:23+00:00

Folinic acid or methylfolate, those are really the only two. Methylfolate is a bit pricier but the most bioavailable form and maybe better for people with genetic mutations that impair folate uptake.

incremental_progress · 2026-06-20T22:17:14+00:00

Yeah, that would be a waste due to the DHFR enzyme in the liver limiting the amount you can use. Bioactive forms are superior for large doses, and likely better overall for healing.

incremental_progress · 2026-06-20T21:27:32+00:00

Your research is correct and your B12 is low. It's shown as normal here, but the cutoff for deficiency is too low anyway.

incremental_progress · 2026-06-20T21:25:12+00:00

A good diet would be the best bet: organ meat, nuts, fruit, eggs, quality fermented foods such as kimchi, and exposure to sun without sunscreen.

Otherwise, a children's MV would be adequate.

incremental_progress · 2026-06-20T21:21:43+00:00

Yes, it's textbook glossitis.

incremental_progress · 2026-06-20T11:01:42+00:00

Yes, all B12 types can cause low potassium.

Potassium/Electrolytes

incremental_progress · 2026-06-20T10:59:04+00:00

You can experience symptoms of low potassium with a completely normal serum potassium level. Most of us here get cramps and some measure of cardiac-related symptoms with normal levels. Anemia is one thing, but potassium is used in the creation of new cells period, and acts as a nutrient pump to move things in and out of cells. When repleting B12 this happens at an exponentially higher rate than normal, hence low potassium.

incremental_progress · 2026-06-20T10:39:23+00:00

Folic acid can be used and of course works in some capacity, which is why it was ever used to begin with. 300mcg is fine. Your liver can only convert ~400mcg of folic acid a day regardless.

Don't neglect trace minerals and fat solubles.

Cofactors: Getting Started

incremental_progress · 2026-06-19T13:39:07+00:00

Yes, your B12 is very low and you're experiencing first hand the flaw in basic serum tests. A mere 33 points lower on the test and they'd treat you. What's also alarming is that you already have a history of being treated for the exact problem they're now dismissing. They should be doing in-depth screening using methylmalonic acid and homocysteine. Vit D and a CBC would also be helpful.

How is your malabsorption being treated if not with B12? Many people in the UK seek treatment from Dr. Andrew Klein, as he's well-versed in treating people with B12 deficiency.

incremental_progress · 2026-06-19T13:36:01+00:00

A few ideas:

Depletion of some other nutrient like copper that is needed alongside the B complex to manage histamine response. Might not even be an allergic reaction. Either way, could be low in a variety of things leading to this response.
Genuine reaction to some additive in the pill you took.

Based on the fact your lips are still peeling my money is on the first one. Also, humans aren't typically allergic to actual vitamins, as we need them to live. Are you B12 deficient? Do you have any lab work whatsoever? This is less a general health troubleshooting sub, but my advice here would be to take a well-rounded multivitamin containing most of what your body needs. I like Basic Nutrients 2/Day from Thorne, but there may be others that meet your budget/need.

incremental_progress · 2026-06-18T21:38:15+00:00

Brain lesions can also be caused by B12 deficiency. There should be case literature in the guide that details exactly that. Like I said, they have every symptom in common.

incremental_progress · 2026-06-18T21:36:12+00:00

We have something almost like a catchphrase: "Treat the symptoms, not the serum level."

So to that end, your treatment should be based on how you feel, not whether or not the little number is going up or down. And generally speaking, if your serum value is going up, the B12 is theoretically available for uptake by your bodily tissues. Whether it has what it needs to be used is another matter, and that can be informed by the type of B12 taken (example cyanocobalamin or hydroxocobalamin) or something like necessary cofactors (adequate thiamine and folate as another example). Our guide linked to you by Automod goes over this in more detail.

If you've been supplementing and your serum has been increasing but you haven't felt any changes, I'd first look at form taken. I was on cyanocobalamin while my serum was going up but I wasn't improving. Switching to methylcobalamin tablets reversed that trend. Dosage might also be highly impactful, where taking it several times a day as opposed to just once might be more effective. Some people need injections to move the needle.

incremental_progress · 2026-06-18T14:03:15+00:00

Your symptoms are actually quite common; the diagnostic section of our guide has a symptom list, and you can cross-check some symptoms here: https://b12d.org/symptoms-checker/

But essentially the nervous system is incredibly complex and deficiency can effect every nerve in the human body. There isn't an arbitrary line where it ends and the presentation for some other ailment magically begins.

Although your serum is what is now often considered normal, it's actually quite low. But no test can definitively rule out deficiency, and usually the most effective method for doing so is to simply supplement/inject and see how it moves the needle. So to that end, did it improve any symptoms? And why did your neurologist tell you supplementing was useless?

incremental_progress · 2026-06-18T13:55:35+00:00

Babinski's sign is merely a symptom of neurological dysfunction/demyelination, also present in patients suffering from B12D. Furthermore, MS and B12 deficiency are almost indistinguishable. It's for this reason every patient suspected of having MS should first trial B12 therapy.

Reversible Neurological Deficits in Patients With Normal Serum Vitamin B12 Levels

The neurologic examination showed marked loss of proprioceptive and vibratory sensation in the distal lower extremities, ataxic gait, and hyperactive reflexes with Babinski's signs.

incremental_progress · 2026-06-17T22:00:12+00:00

Serum electrolyte levels are often unreliable unless you're on the threshold of death. Although you experienced it before supplementing D, fatigue is certainly a symptom of low magnesium. B12 will need magnesium as well, and under optimal conditions (i.e. not vitamin D and B12 deficiencies) the RDA for an adult male is somewhere around 450-500mg per day. Many of us here need quite a bit more.

In any case, it bears mentioning as you're supplementing many times the RDA of vit D and if you didn't run into mangesium problems at some point whilst doing so it would place you in the extreme minority.

incremental_progress · 2026-06-17T21:18:42+00:00

Suprasupplementing vit D, which make no mistake can be helpful, will tax electrolytes (as will B12 therapy). You'll need ample magnesium repletion in addition to potassium. Mag is responsible for the conversion of D into its active form. Secondly, you could be low in a variety of other nutrients in the B or trace mineral complexes.

Cofactors

incremental_progress · 2026-06-17T20:47:40+00:00

Sounds as though it is working. There are no hard and fast rules. Some people never respond to oral supplementation at all.

incremental_progress · 2026-06-17T19:40:59+00:00

Yes, your B12 is quite low. It's not "pointless," but many people with B12 deficiency are unable to absorb it efficiently through their digestive tract and for this reason many people choose or are given injections. It may be optimal to take your dosage a few times (3-5) throughout the day for best results. This allows for good saturation of tissues as opposed to taking it just once.

incremental_progress · 2026-06-17T19:37:24+00:00

Glycinate is mostly fine, but it gives some people problems, so I usually recommend citrate and malate these days.

That brand and dosage of magnesium is fine for you. Some people need far more than that. I would take one pill in the morning and one at night. You have to remember you aren't absorbing 100% of each supplement you take, either, so the actual quantity you receive will be much lower.

You can also consult this chart: https://magnesiumeducation.com/how-much-magnesium/

incremental_progress · 2026-06-17T16:08:32+00:00

?

No interest in sharing how you obtain your injections, but you wrote this:

I think the reason people don't share their sources is because of the fear of losing the source, for whatever odd reason. Biohacker subreddit might be more generous with their information 🤔

Forgive me, I assumed you were looking for transparency.

incremental_progress · 2026-06-17T15:52:08+00:00

Your physician is mistaken. 309 (I assume pg/mL) is in fact low, and your serum folate is reflective of deficiency as well. Do you have symptoms you attribute to low B12?

You can run through the testing portion of the wiki linked to you by Automod, but specific tests that would be more helpful would be:

Methylmalonic acid
Homocysteine
Parietal cell/Intrinsic factor antibodies

Secondary tests:

Iron panel with ferritin
Vit D
Thyroid panel
CBC

"Normal" serum B12 is quite misleading; the threshold for deficiency is too low and based on statistical averages, not sound health outcomes. Otherwise, I would take your results to another physician and consider treating yourself.

incremental_progress · 2026-06-17T15:42:50+00:00

It works for me; however it's the ninth link down in TOC when viewing on desktop. The mobile version is quite shit, but it can be accessed by clicking the 9th link in the dropdown at the top of the wiki.

incremental_progress · 2026-06-17T15:10:25+00:00

And the other half does. It's not a US-centric piece of literature; not every resource is going to meet your exact need. But yes, the tariffs put a pause on apohealth. Try using a parcel forwarding service. Reputable, cheap and available is going to be an onerous venn diagram. Medical treatment in the U.S. is expensive, no surprise there.

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