Pernicious Anaemia Society
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B12 or thyroid?


This might not be able to be answered yet but I had my 6 b12 loading doses early Feb. Blood test a couple of weeks later it was around 1100 (140-724)

Hadn't noticed a difference was still feeling crap so at this point was started on 25mcg levo with TSH 4.7 (0.27-4.2) t4 and t3 low in range. I felt better after about two weeks on it, lasted about a week then felt crap again the rest of the time.

Had a blood test just past the 10 week point of my last injection and 7 weeks after starting Levo.

B12: 399,

tsh: 6.53 t4 and t3 low in range.

Same ranges. At this point levo increased to 50mcg. Felt no change until the day after b12 injection 8 days later.

I know it can take a few days to notice a thyroxine increase so was it just coincidence that it was the day after b12 injection or could it be b12 that's made the difference this time? I honestly felt no change after the first 6. I wouldn't have even known I'd had them if I didn't have sore arm.

I was started on b12 when it was 238 so it wasn't massively low in the first place.

So for it to be 399 10 weeks after 6 injections is that low enough to cause symptoms again?

And if after 6 injections it went up to 1100 and dropped to 399 after 10 weeks, will it fall quicker now I'm on 1 every 12 weeks?

I think I'm probably being impatient already considering self medicating b12 and possibly levo eventually. I just want to feel well again :(


14 Replies

Hi Salphy a lot will depend on how long you were deficient in B12 and it is not uncommon for some symptoms to appear to get worse before they get better as the B12 starts repairing the damage done to your nervous system.

It would be a good idea to have your Folate level tested. 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.

I am not a medically trained person but there are others on here who will be able to answer any more questions.

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Thanks Clive :)

I've had folate tested and I'm prescribed 5mg daily. Iron levels are OK.

It's just so annoying when they all cause similar symptoms it's so hard to know what the main culprit is :(

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serum B12 is problematic as a test to diagnose B12 deficiency and needs to be taken in context which could include other tests (full blood count to look for macrocytosis), MMA, Homocysteine - but would mainly include symptoms.

Once treatment have started normal range doesn't apply and results are only significant if they come back low - and to be honest I would consider 388 to be a low result for someone who has had a B12 shot in the last 10 weeks - means your kidneys are quite efficient at removing the B12 (presumably hydroxocobalamin) from your blood.

Can't really advise on the thyroid though do feel concerned if you are doing this without medical supervision as it is something where you can overdose. Please discuss with your GP.

It isn't uncommon for people to notice no significant change with loading doses. B12 is used by a lot of processes in the body and one of those is the production of healthy red blood cells (also uses folate). If your symptoms are caused by the anaemia that results from there not being enough B12 in your cells then it will only clear as your red blood cells are replaced by new ones - the average life of a red blood cell is 120 days so it is obviously going to take a few months for this to correct.

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and yes, as clivealive says - you will need folate as well - if your levels were towards the bottom of the range then it is quite easy to become deficient when you start treatment for B12 deficiency/absorption problems

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Thanks Gambit. Sorry I should have been clearer, I'm not treating my thyroid myself currently it is prescribed by gp. My dad is with the same gp and they will not increase his dose as he is back within range. He is in the upper end of range and still symptomatic. It feels like its been a fight to get started on levo so if I was to hit the same point with them I will probably increase the dose myself.

I'm also prescribed folic acid 5mg daily and that is within normal range.

I basically was wondering if 399 is typical 10 weeks after 6 loading doses.

And if I'm going to struggle now I'm at one every 12 weeks.

Because I'm assuming that if I started at 238, 6 injections took me to 1083, After 10 weeks I was down to 399, then had the injection 2 weeks later.

Then Im likely to have been lower than 399 at this injection? And one injection probably won't get me as high as 6 did? I now have 12 weeks until my next one, so by then it will likely be even lower than 399?

Or is that not how it works?

At what point would you consider additional injections and how would you know how far apart to have them? There's no chance of my gp giving them more frequent. And like I said with the thyroid not being right and this I don't know which one my symptoms are caused by or treatment will help most. I haven't felt well for such a long time any improvements have been hard to notice until I go downhill again x


do you have any neurological symptoms - tingling in extremities, pins and needles etc? If so the BCSH and NICE guidelines are maintenance shots every 2 months and you could try using that - write to GP/practice pointing out that they aren't actually treating you per guidelines. (The loading regime is also different).

Excess B12 is removed by kidneys and passes out in urine but rate at which this happens varies from person to person - and the rate of removal gets higher as your serum levels get higher - about 50% of the amount put in in an injection will be gone in the first 24-48 hours.

Do you know what caused the B12 absorption problems?

Suggest that you post on TUK in relation to thyroid issues.


Thank you, I have posted in thyroid UK but since i only had an increase 3 weeks ago there's not much more I can do until my next blood test in 4 weeks.

I have been getting pins and needles but I put it down to posture. I have problems with my neck since a car accident but that could just be the physiotherapist in me.

They're not consistent though, I'd maybe have it for half a day in a really random area like my forearm then won't get them again few months and it would be somewhere different.

If it was that would they not just return when you went back to 3 monthly as your b12 would drop again?

I'll bring it up at my next appt as at the time she prescribed it I wasn't getting them or certainly hadn't thought it was worth noting.

No not yet, she said we could test for PA but didn't really seem that bothered. We haven't really spoke about it since other than my first appt after the loading injections when I told her I hadn't noticed a difference she kind of switched towards focusing on the thyroid then instead.

I had a full blood count after the loading doses. But nothing flagged up other than slightly high iron and cholesterol which she wasn't concerned about and a high hormone that she said we could get an ultrasound for PCOS if there's no change once thyroid is controlled.

Thank you again x

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Thyroxine has about a 6 day half life, so it takes ~18 days to adjust to new dose, three half lives. What are your main symptoms? TSH 6.54 means still hypothyroid.


Thanks Brian, I'd heard this half life stuff before but didn't know what it actually meant. I would have been day 18 from my new dose on Monday.

Main symptoms are the usual fatigue, weight gain, dry skin, irregular long periods, high cholesterol. I also have adult acne on my chin which they may be looking into PCOS. I get the sighs though not so much recently. Occasional random pins and needles. What I can only describe as vibrating vision when I look at lines (radiator, door frames etc) and tremor than I've had since I was about 15.

They put it down to PTSD but I'm in a better place now at 25 and it's been particularly bad today. After some gardening to the point it's effected function - basically shook the salad off my sandwich I was tying to eat before...

Seems after this dose increase/b12 injection I still feel tired but finding it harder to sleep. Not able to fall back to sleep after being waken in the morning and taking longer to get to sleep. Have had slot of headaches the last 2 days though so could be that. Thanks :)


Hypothyroid symptoms:


Increased sensitivity to cold


Dry skin

Weight gain

Puffy face


Muscle weakness

Elevated blood cholesterol level

Muscle aches, tenderness and stiffness

Pain, stiffness or swelling in your joints

Heavier than normal or irregular menstrual periods

Thinning hair

Slowed heart rate


Impaired memory

I just reviewed, and saw longer thyroxine half life when hypo, more like 9 days. If you've been hypothyroid for a while, euthyroid might not feel "right" at first. Maybe take thyroxine and B12 (if applicable) in AM, as both can stir you up a bit re sleep. TSH should really fall below 3 once euthyroid. Prudent to allow a month to equilibrate to new dose, up or down... If you've been using caffeine to cope with hypo, maybe time to cut back on that?


Yes I have most of them.

Not sure how long exactly. I'd say the weight gain started around 2011. But prior to this I had issues with food so it's kind of felt like I recovered and started putting the weight back on and it just never stopped. I used to think I'd just ruined my metabolism before getting tested.

I always needed to sleep after getting in from school but I was very active. My levels have only been sub-clinical (UK) since first test Dec 2016 so I don't know if it could have been that far back.

My B12 is injected once every 12 weeks. I usually take my levo at night then folic acid in AM because I'm more likely and do forget to take tabs in the morning. I don't have trouble getting to sleep at night but when feeling like I need a nap through the day it's taking longer. But like you said it might just be feeling weird to be finding this difficult.

Maybe I'm in a bit of a limbo of some improvement to not be able to sleep as much but not enough to not feel like I need it.

I don't think I've really ever had a lot of caffeine. I don't drink tea, coffee, fizzy or energy drinks. I do have a bad habit of a bit of chocolate every day but only the small children's kinder bars. I don't eat any dark chocolate so will be very little caffeine anyway.

Thanks for all your suggestions :)


There probably is a little bump in thyroxine after each dose, so morning dose might prop you up through the day. Also, being euthyroid will help, and you aren't there yet. Good luck! Plenty of room re more synthroid.

Dosing in Specific Patient Populations

Primary Hypothyroidism in Adults and in Adolescents in Whom Growth and Puberty are Complete

Start SYNTHROID at the full replacement dose in otherwise healthy, non-elderly individuals who have been hypothyroid for only a short time (such as a few months). The average full replacement dose of SYNTHROID is approximately 1.6 mcg per kg per day (for example: 100 to 125 mcg per day for a 70 kg adult).

Adjust the dose by 12.5 to 25 mcg increments every 4 to 6 weeks until the patient is clinically euthyroid and the serum TSH returns to normal. Doses greater than 200 mcg per day are seldom required. An inadequate response to daily doses of greater than 300 mcg per day is rare and may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors.

For elderly patients or patients with underlying cardiac disease, start with a dose of 12.5 to 25 mcg per day. Increase the dose every 6 to 8 weeks, as needed until the patient is clinically euthyroid and the serum TSH returns to normal. The full replacement dose of SYNTHROID may be less than 1 mcg per kg per day in elderly patients.

In patients with severe longstanding hypothyroidism, start with a dose of 12.5 to 25 mcg per day. Adjust the dose in 12.5 to 25 mcg increments every 2 to 4 weeks until the patient is clinically euthyroid and the serum TSH level is normalized.


With that referring to synthroid is that US guidelines?

I was started on levothyroxine 25mcg in March for some reason. I'm 25 with no heart problems. Now up to 50mcg since 4th May witg next blood test in 3.5 weeks. Hopefully not much longer till I get on the right dose.

Getting lots of the sighs tonight so really considering self injecting b12. Going to wait and see what my levels are at next bloods and decide from there :)



Sorry, I'm based in US. The principles are the same. The pituitary is the thermostat, so as long as TSH is high, thyroid hormone levels are low. Some room for artistic interpretation, for example, if TSH is just slightly high. Then it is a blend of TSH level versus symptoms. As long as TSH is high or high normal, the oral thyroxine is being added to what your own thyroid makes. As TSH approaches zero, internal thyroid hormone production approaches zero and the oral hormone is all you have circulating. Most people prefer the feel of being mid range, like TSH1 to 3...

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