Pernicious Anaemia Society
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Heart rate increase before injection

I have b12 injections every 3 months. I just have noticed that roughly between a month to 1 week before my injection my resting heart rate increases from an average of 68 to 73. This has been the case for the last 9 months (since I've had a fitbit that measures hr).

To note, I have no fear of injections or worry about visiting the doctors.

Has anyone else noticed this or know a reason this may happen? I'm quite curious.

10 Replies

You probably are running low on red blood cells and you need a higher blood flow rate to get the oxygen to the cells of your body.

And other symptoms that return about the same time, or show up after the jab itself?

It sounds like you are already keeping a log of your symptoms. Provide a list and if you are also keeping severity scores, then a graph of the severity scores over time to your GP when you ask for more frequent injections.

I was able to get both my UK and USA GPs to increase the frequency of my jabs. I now self inject cyano-b12 weekly instead of the normal monthly. I was also at monthly hydroxo-B12 injections in thr UK instead of the 3-month injection.

You typically have to get your doctor through the "i've got a hypochondriac on my hands" phase that we all have to deals with when we ask for increased injections.

Providing a list of all your symptoms for the GP to hold seems to work well especially if there are lots of neurological symptoms

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On the whole I feel okay. Youre right, I do log symptoms. I get tired near my injection and I find my skin gets dry. However, I don't think I need the frequency increasing.

Thanks, you are probably on to something with the red blood cells!


Do you know what your Folate level is?

There is a complex interaction between folic acid, vitamin B12 and iron. A deficiency of one may be "masked" by excess of another so the three must always be in balance. Folic acid works closely with vitamin B12 in making red blood cells and helps iron function properly in the body.


No, I haven't had a blood test in a good 2 years. I do give blood and my iron levels are generally fine, but I never book it near the end of the 3 months between injections. Thanks, I'll look into how they work together.

To note, despite becoming more tired near the injection I feel fine. I am curious about the trend in my resting hr.


I think a good number of us on here eschew the "one size fits all" syndrome so many doctors adhere to when prescribing injections.

I've had P.A. (a form of B12 deficiency) for more that 45 years and for nearly 40 of those I lived in complete and utter ignorance of what it was all about as I never knew anyone else with it.

I was originally put on cyanocobamalin B12 1000mcg every four weeks and down through the years because I sometimes "felt the need" I used to "slip in" the odd three week appointment with the nurse. She "caught me out" six or so years ago and refused to give me an earlier injection than the four weeks it said on the prescription and "reported me" to my doctor. He also refused to vary the frequency saying that the neurological symptoms I was getting couldn't possibly be the P.A. because I was having the injections and I would just "have to do what it says on the tin" (with apologies to Ronseal).

In 2010 I joined the Pernicious Anaemia Society and on the then forum asked if I was the only person in the world to "feel the need" in the run up to their next B12 injection and I was amazed at the responses. I was not alone.

Eventually I wore my "one size fits all" doctor down and to start with he "allowed" me to have the "occasional" three week injection when I felt the need and now that is what I am on permanently.

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It may not necessarily be that there are any actual changes in your blood. B12 is also used by the nervous system to regulate resetting neuro-transmitters so if there isn't enough B12 this system can start to go a bit haywire again so your brain may not be getting accurate information about what your oxygen levels are like, so may think that you don't have enough oxygen so its trying to deliver more oxygen when it doesn't really need to.

One common symptom of B12 deficiency is called the sighs - trying to breath more deeply to get more oxygen in to the lungs. This symptom isn't always connected to anaemia and can persist long after anaemia has actually cleared, or be present when there isn't actually any anaemia showing up in the blood work.


Interesting! I do find myself yawning a lot, especially at the gym. Do you think yawning is similar to the sighs?

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its the same principle certainly - it is about getting more oxygen into your lungs

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Oh my gosh that's the first time anyone has labeled this the "sighs." I get those when I am iron deficient but now that you say it I'm probably b12 deficient at the same time!

I have just started jabs again after a long long time of methyl tabs under my tongue. (Neuro doc said shots are somewhat better than sublingual...maybe he means absorption-wise if one has issues with absorption). My RBCs are always low, too large, and have more iron in each than they are supposed to. A GI doc told me these things should resolve with supplementation of B12 but I've never gotten a "normal" result.

What is the experience of others here? Do you ever get within normal range?



what are your folate levels like. Macrocytic anaemia is a symptom of both B12 and folate deficiency so if it isn't correcting may be something to do withfolate.


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