Pernicious Anaemia Society
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Can b12 def cause low grade fever and night sweats??

Hi Everyone,

I’m only 37 years old and recently realized that a source of my many health problems are B12 related but a couple of my symptoms strike me as weird and do not seem to be alleviating with injections.

I have the following symptoms:

- brain MRI stating generalized cerebral atrophy but my memory is fine

- problems with my balance where I feel I’m about to fall over all the time

- random muscle twitches

- my body feels like it’s vibrating constantly

- my head trembles visibly

- my vision is all foggy like I’m looking at the world through a foggy lense

- head pressure

- dizziness

- trouble walking and standing for very long

- fast HR (always, at rest and standing)

- always tired

But interestingly, I also have a low grade elevated temp (between 37.3 and 37.7 C) everyday and I sweat every night...I’m just wondering if anyone had these symptoms. I’ve been getting injections almost every other day for the past month, some things are very slowly improving (balance is a little better, mental clarity a little better, fatigue a bit better, trembling a bit better but still there and head shaking a bit better as well) but this temp and the night sweats remain.

Anyone have these symptoms as well with b12 deficiency??

The other thing is that I was diagnosed with C Difficile, was treated for a month and doctors said I’m clear now but I still struggle with loose bowels everyday. I think that this is why I’m not absorbing b12 but doctors don’t seem convinced...I’m so confused and hoping someone else has had some experience with all this before.

Thanks so much,


30 Replies

Chitra, different symptoms subside at different rates so it may be that.

B12 is involved in maintaining your immune system and low grade fever is actually one of the body's defence mechanisms for fighting infection so it may be that your body is trying to clear your body of things that have been around for a while but you haven't had the energy to fight.

If you were treated with antibiotics it may be worth checking exactly what antibiotics you were given as some can interfere with B12.

Have you also been checked for thyroid problems - your symptoms also sound as if they could relate to hyperthyroidism/grave's.


Thanks so much for your reply! I will check on the antibiotics, bc yes...I was ok vancomycin for 1 month because of the C Diff. I did have my thyroid checked, they also checked for parathyroid and everything came back normal. As a test the doctor put me on the eltroxin to see if it would alleviate my symptoms but after taking it for two weeks it caused crazy palpitations that sent me to the ER, so the doc is saying thyroid issues are definitively ruled out.

It is true that I had zero energy before, I will keep plugging away at the B12 and hope the improvements continue. Tx again.

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eltroxin is used to treat hypothyroidism rather than hyperthyoidism.

If you aren't hypothyroid then it would result in the symptoms of hyperthyroidism, which include palpitations but would also include a raised temperature.

eltroxin can stay in your system for a number of weeks so depending on how long ago you had the trial it could be the cause of the elevated temperature.

Do you know exactly what your thyroid results were? may be worth posting them, along with details of the dose you were on on TUK to see what people there say.


Hi Gambit62,

I took the eltroxin way back in April of 2017, when my all of my symptoms got very bad. Prior to that I had dealt with dizzy spells, fatigue and loose stools for years. I had no idea I should have asked to get my B12 checked back then...hindsight is 20/20:

My Thyroid labs were as follows:

TSH: 1.77 mIU/L

Free T3: 12 pmol/L

Free T4: 4.1 pmol/L

They checked twice over the span of a couple months and both times the values were similar.

Also had low levels of Ferretin and Vit D:

Ferretin low at 24

Vit D low at 60 nmol/L

Tx for all your insights, it helps so much to hear from those who’ve been through this already.


Hi ChitN

Have you got the free t4 and t3 values the wrong way round ?

Your tsh level seems fine, although free t4(assuming it’s 12) and t3 are probably slightly on the lower side.

This could possibly point to a problem with the pituitary or hypothalamus - secondary or central’ hypothyroidism rather than an issue with the thyroid gland itself.

However if low dose eltroxin gave you hyper symptoms it may not be a thyroid issue (however it is worth noting palpitations and hyper sx can also occur with hypothyroidism- and esp on low dose 25mcg it can cause more issues- often 50mcg is a better starting dose to Tx hypothyroidism.)

May be worth looking into supporting your adrenals - look at the HPA axis to understand this better. It could be a knock on effect from one to the other.

However do sort the vit D as soon as possible. Apart from adrenals it will certainly cause many of your other symptoms - it really is a life changer

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Thanks Saya85. I’ve started supplementing with 3000IU of vit D per day. I will be getting rechecked in the next few weeks. Oddly I am “borderline” adrenal insufficient. But when I started taking Cortef (initially 15mg per day and now 25mg per day) my symptoms did not improve. I’ve been supplementing for 3.5 months now, and will start to wean off in the next little while as I don’t want to be on steroids unecessarily.


Oh and yes I did reverse my T3 and T4 values above :-)


think you have T3 and T4 round the wrong way ... and as always -useful to quote the ranges as can vary from kit to kit as well as there being different units.

low ferritin implies low iron - which is probably an indication of an absorption problem - so likely to be the same thing as is causing your B12 to be low

April 2017 means eltroxin isn't going to be a factor.


Oops yes Gambit62, I’ve reversed my T4 and T3! Ok, good to know regarding absorption. I will be asking for h pylori testing next as well as a revisit of if my c diff is truly gone. Tx so much.


Hi ChitN. The symptoms you describe above can indeed be due to B12 deficiency, including the low grade temperature...or problems with temperature control (mine swings between 35 and 37.7).

Neurolgical symptoms can affect the autonomic nervous system...that is the part of the nervous system that works automatically (temperature control, breathing etc.) and this may be what you are experiencing.

Here's a extract from emedicine/medscape:

Nonneurologic symptoms, some of which may also reflect autonomic nervous system involvement, were present in 26% [of people with B12 deficiency]:

Constitutional symptoms, including anorexia and weight loss occurred in 50%. Low-grade fever that resolves with treatment occurred in 33% of cases. Other symptoms include fatigue and malaise...

And here's a link to the full article:

As Gambit says, some symptoms may take longer than others to resolve and there are a multitude of possible symptoms, some of which are not found on many symptom lists (I've never seen any symptom lists that are the same - they all differ).

Here's a comprehensive (but not exhaustive) list of possible B12 deficiency symptoms (bet you'll find yours there - and perhaps some symptoms that you didn't know were symptoms):

It's good that you're receiving every other day injections (the regime for those with neurological symptoms) and it's important that this regime is not stopped too soon GP's who know enough to prescribe this regime sometimes make the mistake of wanting to revert to less frequent injections too quickly, often making the mistake of assuming that if serum B12 levels are high (or extremely high), then the frequency of injections can be decreased. Once injections have started, serum B12levels will be high but this is no indicator of the efficacy of treatment. GP's should look st symptoms and ignore serum B12 levels (unless they're still low, in which case more frequent or higher dose B1# injections are needed).

Here's some information about that: (B12 Treatment Safety / Long Term Treatment for neurological symptoms)

One month is very early in the treatment process and not all the symptoms of B12 deficiency are alleviated immediately, or at the same time...and we’re all different/have different symptoms, and there's no way to predict what will 'fix' first...or when.

There is a cross-over of B12 deficiency symptoms and many other medical conditions (thyroid - as per Gambit - and diabetes etc.) so if your remaining symptoms remain, your GP should want to rule out other potential causes.

If you also have gastric symptoms, might be worth ruling our heliobator pylori (gastric bacterial infection) which, incidentally, can also cause B12 deficiency. Your doctor can do a breath test for this.

If your loose bowel movements continue, your GP might like to rule out other causes (IBS, Crohn's / Coeliac disease etc.) - all of which can result in B12 deficiency.

Information about C diff:

Might also be worth researching the impact of diet post-c diff (I've read that diary products are sometimes troublesome in the post-infective period).

Best of luck ChitN...let us,know how you get on and post again if you need more support or advice.



Thank you for all the info. It’s very helpful. I had no idea that my premature grays could have been from B12 deficiency, not to mention my gastro issues.

In terms of your elevated temp, do you also get night sweats? The night sweats were sporadic for me when my symptoms first got very bad (about a year ago) but now they are daily. Doctors seem so unknowledgeable about B12 and every symptom I mention seems to be met with blank stares. I know I wasn’t like this before and now I’m so sick everyday.


Yes, I did get night sweats and come to think of it...not any more since having B12 injections.

Here's a research paper about B12 and night sweats:

Sorry to say that many doctors are ill-informed about B12 deficiency. Many here find that the best way to deal with that is by becoming well informed and also collecting information and evidence to share with our GP's 😉.

Just thinking about your situation...and assuming that you were originally diagnosed with B12 deficiency and hence the injections...a few tips that may (or may not) help you to start untangling what's going on...

a) people with B12 deficiency often suffer from other deficiencies too. Has your GP tested folate, vitamin D and ferritin (marker for iron deficiency anaemia). Deficient or low levels in any of these can make you feel very ill indeed, and the symptoms are very much like those of B12 deficiency. If not tested, ask your GP to do so. GP's often say results are normal when they're not - sometimes it's where the result is in the reference range that counts. If you want to, you can post your results (including the reference ranges) in the forum for help with interpretation (you are entitled to a copy of all results so your surgery should be able to print copies for you - or give you online access).

Oh...just spotted your reply to Gambit...hope GP is treating you for low vitamin D and ferritin. Not there's nothing about folate? Folate and vitamin B12 work together somimprowtnwt thwt folate is not too low.

b) Have you been tested for pernicious anaemia (IF antibodies)? Possible to test negative and still have pernicious anaemia (approx. 50% of people with PA test negative).

Sorry ChitN...something's come up and I have to go...will return and finish this reply...but maybe not be until tomorrow... (have to post now or it will disappear) 👍


Thank you so much for the info Foggyme. They did not check my folate however on top of my multi and b complex, I’m taking 1000mg of folic acid per day as I read that it can get used up quickly once B12 injections are started. I plan to ask to check my folate level at my next follow up for ferretin and vit D as I hope I’m not over supplementing. I have not been checked yet for PA. I’m hoping my referral to the heamotologist comes quickly as I would hope they would know what to check?? Although my family doctor rolled his eyes at the idea of PA when I mentioned it because I do not have an issue with the size of my red blood cells...I’ve read that this is not always the case. Hoping and praying the Heamatogolist is more informed about PA...


premature greying and PA is a correlation rather than a causal link. Probably an indicator of a genetic factor as PA runs in families. It also has a high correlation with blue eyes.


Hi Foggyme,

I’m wondering how long it took for your low grade fevers and night sweats to subside after getting injections. Every paper I’ve read indicates that this subsides quickly after starting injections but I’m on my 7ths week of every other day injections and my low grade fever and night sweats are still here...


That's not an easy question to answer ChitN because recover takes place at different rates, for different individuals. And some symptoms go more quickly than others.

If symptoms persist, might be a good idea to discuss with your GP and rule out any other potential underlying causes (thyroid issues being one candidate).

Good luck...and sorry for the slow response (haven't been receiving reply notifications so now back-tracking through forum to try and spot anyone awaiting replies 😖😉).


Appreciate your reply Foggyme. Thyroid issues were checked...

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You sound like me! I had all of those issues and the bowel issues, my bowels got so bad I was using suppositories daily because I just couldn't go. It's SIBO, Small intestinal bacterial overgrowth. Gave up gluten & and started taking a probiotic every morning & digestive enzymes with every meal & my bowels started functioning properly again. SIBO will affect B absorption. I also took a strong B-Complex and Magnesium and Vit C everyday.

My SIBO was caused by antibiotics, I'd had multiple courses which wiped all my good gut bacteria out and allowed the bad to overgrow. Eventually things your bowel stops from entering your blood are able to pass through and trigger an immune response and other symptoms like a low grade infection and this would explain the temperature. HR would be because your body is in fight or flight mode and you have elevated cortisol levels as a result.

I also had the random twitching, vibrating, trouble standing for long or even sitting in a chair for long, constant brain fog, dizziness, fish tank vision where i'm looking at the world from inside a fish tank or a video camera.

I had a long period where I was waking up drenched in sweat.

At one point I had a carrier bag full of medications from the doctor, non of which helped with anything. I was even taking Omeprazole when the reality was I had too little stomach acid so why would I want to reduce it further? To improve my stomach acid I took ACV and blended celery and drank it in the morning about half an hour after my probiotic.

Eat as close to nature as you possibly can, ditch the processed junk until you heal yourself. I'm not saying you need to give up gluten or dairy but if eliminating processed foods (mainly refined sugars) and eating healthy foods doesn't work then you should try those options later on. Eat things like oats, carrots, onions, potatoes, leeks, spinach, celery, lentils, garlic, oregano. I made lots of chicken soup jam packed with lots of fresh vegetables and I ate it 3 times a day at one point with gluten free bread (multiseed).

No symptoms anymore and haven't had any for a long time now. I have a perfect functioning bowel and I go daily like a normal person should.


Thanks for all the info mrpenguin!

How long did it take for your symptoms to subside? And did they all disappear completely?

I think my problems are definitely gut and absorbtion related as my stools are very loose everyday and have been for years (sort of opposite to you however). I will try going gluten and dairy free for a bit. I take 2 probiotics a day but have not tried digestive enzymes or ACV yet. I was taking magnesium but found that it made my stools even looser :-(

Did you also have a b12 deficiency? I have an appt with an infectious disease specialist today. How did you get SIBO diagnosed?


How did you get SIBO diagnosed? Ask them about a hydrogen breath test & bring up SIBO (Small Intestinal Bacteria Overgrowth). SIBO is difficult to diagnose and my GI specialist based on everything that had been ruled out suggested it was the cause. Up to 80% of people with irritable bowel syndrome (IBS) have SIBO so the chances that you have it are very likely. If you take Antibiotics you may feel better for a short while but it will come back again because it's not changing anything and is actually killing off more of your good bacteria, the environment in your gut needs to change.

Yes I had B12 deficiency and I took a strong B complex for a few months before moving onto a regular one daily and only taking the stronger one occasionally as I felt I needed. As far as magnesium goes, there are different kinds of magnesium, some cause diarrhoea while others don't. Magnesium Citrate will cause the runs. Chelated Magnesium or Magnesium Glycinate is the one people use for actually increasing levels in the body.

Once I had a handle on things it took around a year till I felt perfectly fine and no longer had constant symptoms taking over my thought process.

How do you take your probiotics? The best way is 1st thing in the morning with a large glass of water to dilute the stomach acid so that it doesn't just kill the bacteria.. This way at least some of it makes it past the stomach.

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mrpenguin. I couldn't believe it when I read your comment. I have doing the docs jobs trying to figure out what's wrong with me. A little background;

About 6 years ago I had a bone tumor in my foot. Then another in my heel. I ended with a bone infection from treatment and surgeries that resulted in my right leg amputated. I first started losing weight(which is weird because I was and have been less active) then I noticed heat intolerance. For the past 4 years I have felt I have been fading. Last spring, my oncologist found my b12 was very low(98). My primary took over and did the instrinic factor and was extremely high. I was then told I have PA. I thought that was the end of the guessing game. I started on daily shots then weekly. Now I take 2 weekly shots. When I first started getting sick, I weighed 133. I now weigh 93. I have horrible nightsweats, heat intolerance, dry skin, racing heartbeat and overall feel horribly off. I had the kid checked a few years ago but they just did t3 and t4. I heard those aren't the only ones needed. I go to my primary tom morn and am going to beg to check my thyroid and also my gastric problems. I just want to thank you for posting. It is a comfort knowing someone shares the same symptoms


How is your bowel function? I would say it sounds like you have SIBO based on what you've said. The weight loss occurs due to malabsorption and the symptoms due to toxins entering your blood stream.

What about your blood sugars? If you don't know it might be worth buying a glucose meter on amazon (They are really cheap), buy some Urinalysis Reagent Strips (I use the the ALL TEST brand 100 strips) they are cheap & on amazon and the same ones GPs use. You can check your urine for Ketones & Glucose & Infection, see if you can't rule out a few reasons for your weight loss other than what I've mentioned.

Nothing worse than being ill and spending month after month waiting for the next appointment which will send you off on another round of tests for something else hoping you will find out what the issue is.

Good luck with the doctor, don't be fobbed off.


Thank you for responding. I was just tested for diabetes and all levels were normal. My bowels were a mess I think because of pain pills from my amputation. I don't take those Any more and bowels are a little better. I did a blood test this morning for thyroid. If it's fine, I'm lost as to what the deal is


Thank you mrpenguin, this is very helpful. I am taking CanPrev magnesium glycinate, only 200mg gives me the runs. I’ve just ordered a non-buffered version from 88Herbs to see if it will be easier on my stomach. I tend to take my probiotics at night. I’m taking saccharomyces boulardii as it’s supposed to help with C Diff but I haven’t noticed much difference. If anything I have a partially formed stool at around 6am and followed very loose stools shortly thereafter. And the stools are like clockwork, everyday same time...

1 year is a long time for recovery. I just hope I recover fully, this has been very tough to go through. I’ve been off work for 10 months already and was hoping to go back soon...


Sounds like many of my Multiple Sclerosis symptoms. I am also allergic to Cobalt, which is in B12:( I hope you find a solution dear!



Hi Kathleen,

Tx so much for your reply. I was checked for that (by 4 different neurologists and an ophthalmologist). I also had 3 different MRI’s of c spine and head with the only finding being generalized cerebral atrophy.


I got the night fever sweats. One of the reasons my gp went on about stress and anxiety. I wish I had never said that to them now because it massively delayed diagnosis and treatment.

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Hi. Thank you for posting. I don't feel so alone now. Hope you feel better soon

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I might have missed it, but what form of B12 are you taking? When I took cyanocobalamin at first first orally, then as shots they both gave me fevers, worse from the shots. They were low grade, but I got fever chills kinda crazy like from my legs! I finally found out I have a MTHFR mutation and couldn't handle the cyanocobalamin form of B12 as I couldn't methylate properly. I'm doing methylcobalamin sublinguals now (along with folate) and the B12 deficiency part of my problems seems to be resolved. Still working on my gut issues that caused it all, but I think I'm on the right track. Thought I'd mention my story just in case your fevers don't resolve quickly and you were taking cyanoB12. Also, once your B12 levels start going up, take Magnesium and potassium. I think I got very low on both as I had lots of problems with twitching muscles & cramping muscles after any exercise and I've now read that it is common to get low in these minerals as our bodies repair our cells from B12 deficiency. You can also split the pills in half if the Mg bothers your stomach. Oh and I've heard that magnesium oxide is the best form of Mg to take.


Hi kngswim,

Thanks so much for your reply. I’m taking methycobalamin. The low grade fevers started much before I started supplementing however :-(. So I think it’s one of my symptoms. It’s interesting that you mention your issues are likely gut related as I believe mine are too.

Do you take potassium pills? If so what dosage? I’m trying to eat at least one banana a day and have 1 cup of orange juice a day. I have lots of trouble with muscle twitches daily as well it feels like my body is constantly vibrating...


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