Thyroid UK
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Stupid question; how do you know you have a b12 absorption problem?

Hi everyone,

This is a bit of a stupid question, but I can’t seem to get it straight in my mind. I currently have low B12. Whilst I await results from a MMA and homocysteine test, I’ve been looking at supplements.

Now I can order sublingual tablets for B12, but I wondered how do you know if you have a problem absorbing b12 through the normal channels? I know that body doesn’t need much B12 daily, so if you are low then either you aren’t getting enough in your diet, or there is a problem. But how do you know that simply taking an increase in B12 as a normal tablet won’t solve the problem? You could take them and see if there was any improvement, but apart from that and having another blood test, how would you know? For reference my anti-intrinsic factor came back negative.

Like I said a stupid question, but something I couldn’t answer myself?

PS. The tagging system is awful, how many times have I mentioned b12 (there's another!) and that's not even one of the tags, and you can't edit them either....

19 Replies

NO question is stupid.

Are you experiencing any symptoms which are indicative of B12 deficiency? What was your blood level when last tested? What strength of supplement are you thinking of using or using? Sublingual and spray bypasses the stomach. But it all depends on how much of a dose is absorbed.

Most people begin to have more energy quite soon. But the effect on red blood cells (if there is megaloblastic anemia) takes much longer. The turnover rate for red blood cells in the circulation is about 90 days. It takes that long for all the old cells to be replaced by better new cells.


Thanks for your reply gabkad, see my response to you below!


If you are going to supplement with B12 it has to be methylcobalamin. If you are low on B12 you should supplement as it is a pro-hormone and can lead to neurological problems. No-one over the age of 60 should be below 500 and it doesn't matter if you are higher than that. Sublingual means that it does directly into your blood stream, that's all. I think many hypo people have low stomach acid which may interfere with the uptake.


I have been supplementing with B12 injections Hydroxocobalamin for a few months, have these not been effective?


Hi cc120, no Hydroxocobalamin is perfect and is effective. Cobalamin just means B12. It's the cyano-cobalamin which is synthetic and methyl-cobalamin is produced in nature.


Hi shaws, thank you, great to know has been effective. Just recently started the methylcobalamin that Hugo Minney (PhD) from the B12 Deficiency Support Group was kind enough to send to me. But when it finishes will be back on my Hydroxocobalamin.


Do you have pernicious anaemia?


Hi shaws, I did have low B12, within range though, and do have a lot of PA /hypothyroid symptoms. Definitely have hypothyroid, probably PA too.


Thanks shaws, as I attempt to explain in my post below, its like a chicken and egg situation. Do I have low stomach acid which is causing problems absorbing B12? And what is causing that? It's like a never ending chain!


Whitenoise, the only stupid questions are the unasked questions.

If you have gut issues affecting absorption of B12, sublingual lozenges, sprays or patches bypass the gut and deliver B12 directly to the bloodstream. You judge efficacy by improvement in symptoms or monitor with a follow up blood test 4 months after you stop supplementing.


Thanks :)

Not sure if I have gut issues, I guess that's question :) I'm also trying to avoid taking supplements straight away based on the advice of hampster1, but it's proving frustrating waiting for my MMA and homocysteine results (nearly three weeks now!)



I have pernicious anaemia and if your intrinsic factor was fine i think you are absorbing VIT B 12 so having supplements and another test for blood levels should be sufficient to re-assure you


Thanks to everyone's replies, sorry it's a taken a while to reply, and thanks for the reassurance about asking my question :)

In answer to some questions, I have the following symptoms:

Poor short term memory



Sometimes problems focusing on an task

Difficulty concentrating sometimes

Easily distracted

Slowness to learn new things or register new instructions

Mood swings (more long term, so could be in a really low mood for a few days/a week. Then can feel better for a few days etc)

Problems making decisions



No ‘get up and go’

Problems getting up in the morning

Tiredness, especially in the afternoon after lunch and early evening

Not as good sleep as in previous years (used to be like a log)

Poor stress tolerance


Low mood, with periods of depression

‘Happy things’ tend not to make me that happy

Poor sense of smell

Some taste of metals in mouth (dental amalgams?)

Cold hands (even if body is warm)

Feel the cold

Dry Skin, especially on face, elbows, heels and sometimes fingers

Rosacea (got worse in the last year or so)


Lots of grey hairs (I’m only in my early 30’s!)

Some hair loss

Father on b12 injections, sister had them in the past (no longer)


I guess the issue I have is that I’ve had some of these symptoms for ages, others for a shorter period of time, so I guess it’s just ‘normal’ to me. On reading about B12 I can identify some of my symptoms. However these also appear in hypothyroidism, Pyroluria, some with Vitamin D and other issues. So it could be anything (or nothing!)

I’ve identified my low B12 at 182ng/l (180-1000), but it’s frustrating to know what is the cause of this, rather than just address the symptoms. My doctor probably thinks I’m a bit of a hypochondriac anyway, and on mentioning a few of the above symptoms, he told me that these were the problems of quite a lot of people, and were "nothing to worry about".


whitenoise, how much T4 or T3 are you taking? Sounds like you are hypo still.

Here in Canada, we pay for our own vitamins and minerals. They are not a government health insurance benefit. Those blood tests you mention are also 'pay to play' so to speak. I looked up the list of unfunded lab tests yesterday and zinc, iodine, selenium, B12 metabolites etc. are all for 'out of pocket'. So is the blood test for gliadin anti-bodies. A number of years ago my daughter paid out $160 for it.

What bothers me is if I have to pay out of pocket, then I shouldn't need the doctor as middleman to order them. At least in the UK the NHS covers a lot of these tests. I know it can be difficult to get a GP to order them but at least once it's ordered, you aren't having to take out your credit card.


I'm not taking any T4 or T3. I've only had the TSH test done and the results were 1.3 IU/ml (0.2-5.5).

While we are lucky in one aspect with being able to get some tests on the NHS, it can be very difficult to get doctors and labs to actually give you the tests though. It's all about cost.

I agree though it must be annoying to have to go through this hassle and have to pay for them. But I bet you don't have a doctor that says "Hmm a test for your zinc levels? That's in the realm of alternative medicine; we don't do that here" !


Oh yes they do.

It's much worse than that: My friend wanted her vitamin D checked. That is 'out of pocket'. Doctor refused to order it. Said 'everyone is D deficient'........... I mean, REALLY? Seeing as how we have to pay for the test ourselves, what business does a doctor have in refusing to test?

Usually I do subversive things: I add tests to the requisition. Doctors can't remember what they order anyway.

I think if a patient has to pay, then a patient should be able to order without some M.D. as middleman. Seeing as how they don't know how to interpret test results anyway, an educated patient with an interest in being healthy should be able to just go into a lab, pay and get the results sent to their home.


Ouch! That is completely bizarre. I agree that if you have to pay for something, there shouldn't be a middle man, or at least the doctor shouldn't have a say so; it's your money at the end of the day.

Sadly I can't change my test forms because they are printed. So if I wrote on them the additional tests would be ignored.

Too right on all counts! They don't know how to look at the results, they simply say "normal" or "in range" anyway!

What also annoys me is when (like with Vitamin D), you finally get the doctor to agree to getting it done. You have the blood drawn, but then a few days later when you phone up about test results you are told that the lab refused to do the test! Apparently the sample is kept for two weeks so if the doctor 'insists' they might do the test!

Luckily there is now a Vitamin D test where you can do a finger prick blood spot test at home and send it away. A few days later and they email you the results. It's £25, but it's a lot less hassle and faff.


Your B12 is seriously low. Are you aware that you can have neurological/nerve problems and even research points to alzeimers etc.

Your GP should be proactive to find out your cause of near deficiency of B12.

He should be able to positively get you a diagnosis and take note of your family history. It is too serious not to push for a definite diagnosis. Don't be messed about any longer. My mother died through neglect of her GP.


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