B12 injections vs just taking oral B12, is there actually a difference if you're not deficient?

Posted by fasted_scientist in Beginner Questions - 1 points, 4 comments.

Been looking at the B12 injection profiles on here and I'm a bit sceptical tbh. The standard line is that injectable methylcobalamin bypasses GI absorption so you get way more bioavailability, and that makes sense if someone has pernicious anaemia or some malabsorption issue. But what about someone who just wants more energy or better focus and their bloods are already normal?

Oral B12 is cheap, easy, and even at sublingual doses you can get pretty high levels in the blood. I've seen people on here saying they felt a real energy kick from 1000-5000 mcg injected 1-3x a week, but I reckon a lot of that could just be placebo or the novelty of injecting something. The half-life is about 6 days so it's not like you need frequent shots either.

Not trying to bash anyone's experience, genuinely curious. Has anyone here actually done both oral and injected B12 and felt a clear difference between them? Or got bloodwork showing injectable pushed levels higher than high-dose oral couldn't? Would be keen to hear it because right now I'm struggling to see the justification unless there's an actual absorption problem.

Comments

• busykatie: I tried both a while back, oral sublingual at around 2000 mcg daily and then weekly injections for about six weeks, and honestly i couldn't tell a difference in energy or focus either way, but that's just me and i wasn't deficient to start with so maybe that's the whole point. One thing that bugged me though is people comparing serum B12 levels like that tells you everything, because serum can look great while intracellular status is a different story, and that's where things like MMA or homocys
• formermiles: Not gonna lie katie you nailed it with the MMA and homocysteine point, serum B12 is basically useless on its own. I had a buddy whose serum was like 900 pg/mL which looks great but his MMA was elevated, turned out he was functionally deficient despite "normal" bloods. If anyone is actually curious whether theyre getting benefit from injections vs oral, MMA is the marker id wanna track, not serum.
• fasted_scientist: Cheers for that, though ngl I don't think I actually mentioned MMA in my post, you might be thinking of a different thread. But you're spot on that serum B12 alone is a rubbish marker. That buddy example is exactly the kind of thing that makes me wonder if some people walking around feeling rough actually are functionally deficient despite normal bloods. Did your mate end up sorting it with injections, and did he actually feel different once MMA came down?
• fasted_scientist: Cheers for that, that's basically what I suspected would happen for someone with normal bloods. The MMA and homocysteine point is spot on though, I'll give you that. Serum B12 on its own is a rubbish marker for actual tissue levels. Did you ever get MMA or homocysteine checked during either phase, or was it just serum you were looking at?

Community discussion - research and educational context only. Not medical advice.