Pernicious Anaemia Society
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How much B12?

My serum b12 level were high at the last count (750) but I have many b12 deficiency symptoms. I've been taking hydroxycobalamin, adenosylcobalamin and methylcobalamin at a combined dose of around 10 mg. The initial side effects subsided and the symptoms lessened, but I plateaued. I'm increasing my dose to around 16 and the side effects are coming back (feeling unwell, very blurry vision - some of them have gone or become less). How high do you think I should keep increasing the dose?

Thank you for your help,

9 Replies

B12 deficiency shares many symptoms with other conditions, especially hypothyroidism. Have you has your thyroid hormones checked.

16000ug a day seems an awful lot. It's almost certain that you're throwing most of that straight down the toilet. The body can only carry a certain amount of B12 in the blood. Anything above that will get passed in the urine.


We throw most of down the toilet any way though, don't we? Plateauing made me feel I needed more and having taken more, worsening symptoms confirmed to me, with the discomfort of my healing cells, that I did need more. I was wondering if anyone else has gone through this and, if so, how much more they had taken and for how long.

Thank you.


Taking that much B12 will likely drop your folate and potassium. Being low in these will also make you feel rough as a badgers behind 😜

Are you taking folate and eating potassium rich foods?



I plateaued until I increased my folic acid intake. You could try that and a comprehensive multivitamin and mineral supplement. And add in extra Potassium rich foods/drinks.

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I have read that some people can experience a drop in potassium levels when supplementing B12.

Have you had recent tests for folate, iron, full blood count and potassium?

People can vary in what B12 delivery methods they find most affective eg sublinguals, injections, skin patches, nasal sprays, oral sprays, tablets.

I eat bananas and sometimes drink coconut water as sources of potassium.


Yes, I am supplementing with potassium and methyl folate and fairly recent bloods were normal. I upped the methyl folate from 1 mg to 1.25 mg and it did seem to help. Thank you for your replies.


Sorry for just jumping in without having read all the other comments but do you know if you can absorb vit B12?


I think I must be absorbing some, or I wouldn't be here! I haven't had an active B12 test, but it looks like I am lacking holocobalamin, which means I find it a lot more difficult to get the B12 into the cells. I also have a mutation in my genes which points to a possibility that I am not recycling B12.


I'm not sure how you can assume a lack of TC2 (the protein that transfers cobalamin into the cells) without having a holotranscobalamin (active B12) test.

The first thing you should do is to get a methylmalonic acid (MMA) test (and possibly homocysteine - although that test is complicated because the analysis must be done with 2 hours of sampling). If your MMA levels are high then it means your B12 isn't doing its job properly. It's a pretty accurate and specific (unless you have kidney problems) test.

Once you've determined that your B12 isn't doing what it should so, then it's time to check possible causes. An active B12 test will tell you if the levels of that are OK. About 43% of caucasians (including me) have a genetic defect, 776C>G - part of the TCN2 gene, that results in lowered abounts of TC2 being produced.

Another possible genetic problem is with the genes reponsible for methylation, MTHFR.

I'm not sure which genetic change would hinder B12 recycling. If you have PA then your body will not produce enough Intrinsic Factor to properly absorb B12. That's B12 that you consume, or B12 secreted by the liver into the bile and, hence, the small intestine.

Even with a total lack of intrinsic factor a small amount of B12 will be absorbed from the gut, which may be why you need to consume such huge amounts. If this is the case then other routes of absorption would probably work a lot better. Sublingual, nasal and dermal supplements are all available and people have reported beneficial results from all of them.


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