Pernicious Anaemia Society
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B12 levels drop very quickly- cause unknown. Frequent shots needed

Hi there,

I am new to this site and have been doing lots of reading on it. My word, what a supportive bunch!

I am 35 years old and since having a child almost 3 years ago, I've had issues with my B12.

I am lucky enough to be able to have frequent blood tests to check my levels and I'm pretty much able to know what reading I'm at before being tested by the way I feel, which is then later confirmed by the bloods.

I need weekly to bi weekly injections and if I fall behind with this, I need two or three in a week to boost me back up. I am ok if my levels are about 600. 400 i start feeling overwhelmed, exhausted, unable to cope daily. If I drop to anything below 300 I cant function due to severe fatigue and affects me enormously mentally.

My issue is, why do my levels drop so rapidly??

All other bloods are always checked and are good. Colonoscopy and gastroscopy both good. Ive been told its just my body doesnt seem to absorb it at all. Its not diet related.

Within 4 weeks my levels drop from 1500 to 600... 2 weeks later I wasnt coping at all and it must have plummeted further.

Just wondering if this rings true for anyone else or if anyone could shed any light.

Any other advice would be normously appreciated as I just dont understand why this is happening... and continuing to happen.

Many thanks

5 Replies

Have you had your kidney function tested?

B12 is eliminated in the urine, but then almost all is reabsorbed. If there were a problem with this reabsorption then that may result in very rapid elimination.

1 like

The normal frequency of shots once a month was based on what happens in the average person - some people will remove B12 in kidneys faster than others, some slower - and for some it will be much quicker and for others it will be much slower - you are just at the much quicker extreme.

Human's aren't averages - and we all vary from the average - just some of us do it more than others - look at height. B12 just happens to be something where peope seem to vary a lot more than with other things, so it particularly highlights the dangers of doctors just responding to test results and treating the mythical average person.

I'm not sure it is particularly something to worry about unless you are experiencing other problems.

Speak to your GP about a kidney function test as suggested by fbirder if you are worried


Thank you for taking the time to respond.

Yes, you're certainly right about us all being different. I'm certainly no average ;)

I didn't realise kidneys were related, so will discuss with my GP.

Thank you again


"I am 35 years old and since having a child almost 3 years ago, I've had issues with my B12"

Just wondered if you were aware that nitrous oxide,which is in "gas and air" used as pain relief in labour, can affect B12 levels in body. see link below.

UK B12 websites


the PAS are helpful and sympathetic and can point you to useful info.


Have you been tested for PA (Pernicious Anaemia)?

01656 769 717

B12 books

"Could It Be b12" by Sally Pacholok and JJ. Stuart

A very comprehensive book about B12 deficiency.

What You Need to Know About Pernicious Anaemia and Vitamin B12 Deficiency by Martyn Hooper. Up to date with UK B12 guidelines

"why do my levels drop so rapidly?? "

Just wondered if you had ever had thyroid tests or a test for coeliac disease as some symptoms overlap with those of b12 deficiency.

I am not a medic just a person who has struggled to get a diagnosis.


I was also going to suggest the PAS site but also to check if your doc can give you the active form of b12 methylcobalamin it could be that your body doesn't have the enzymes to activate the b12


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