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Thyroid UK
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Vitamin B12

Hi. I have been on levothyroxine since March this year first 25mcg the 50mcg. I've gone up to 75mcg the last 3 weeks as I can feel the symptoms returning gradually. I saw my doctor today and he advised having bloods done again including vitamin b12, iron, folate, ferritin and selenium. My last B12 result in May was 275, ferritin 50, folate 11.1 (no iron), vitamin d 86. My question is does anyone know what vitamin b12 should be with people with hypothyroidism? Any advice please. Thank you in advance x

6 Replies

The B12 test has various ranges - however Sally Pachlok who wrote the book - Could it Be B12 ? - suggests a level of around 1000 to prevent cognitive decline. We have to consider that when we have B12D - it can be a neurological condition as it affects the nervous system.

Even results below 500 can present with neurological issues. In Japan the range starts at 500. The blood test result is notoriously unreliable - in as much as only around 20% of the result is available to reach the cells where it is needed. Hence the need to have GOOD levels. 20% of 1000 is just 200 - so I guess you can see the scenario.

What are you supplementing and how much ?

I am not a medical bod - just someone who has learnt the hard way !


Thank you. I'm only taking Vitamin D oral spray and levothyroxine 75mcg. No vitamin supplements. Any you can recommend ?


I would also take Jarrow Methylcobalamin B12 lozenge - the 5000mcg - keep under the tongue to ensure good absorption. Also take a good B complex to balance all the B vitamins. If you are taking a D spray - does it also contain VitK2 ? If not then it is prudent to take it to ensure calcium is sent to the bones and teeth and not left circulating in the blood. D increases calcium absorption.

It would appear you need something to boost iron levels - sorry I do not know the iron products in the UK as I am in Crete. Also VitC helps the absorption of iron.

Am sure you should be taking other things - but that will do for now !!

Please go to the main Thyroid UK website - where there is excellent information about vitamins and minerals when you thyroid issues.


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Hi Marz

Just wondered if you've had or heard of similar experiences. I've been taking the Jarrow 5000ug for six days now and I feel sick a lot of the time also feel light headed?



No I have not read of that experience ! Are you keeping the B12 under the tongue until dissolved ? That way nothing should go into the stomach to make you feel sick :-)

I felt lightheaded when I had a T4 dose increase and felt quite unwell. Do you have problems with converting your T4 tablet into T3 - the active thyroid hormone ? If you have some results you can share - maybe we can spot something. Just a thought. If Levo is not converting it can make you feel unwell.


The recommendation is 1,000 for B12. Doctors are happy if we're somewhere in range. We can supplement with B12, sublingual methylcobalamin and they dissolve under the tongue and not the stomach. We cannot overdose as excess is excreted.

Your dose of levo was low to start with unless you are very frail with a heart disease. 50mcg is a starting dose and since March you are only on 75mcg which is quite low.

When you get your next blood test, make the appointment as early as possible and fast (you can drink water) leave about 24 hours between your last dose of levo and the test and take it afterwards.

The aim for the TSH as GPs only seem to diagnose on this is around 1 or lower or suppressed.

Always get a print-out of your blood test results from now on, with the ranges, for your own records and so that you can post if you have any queries.

I hope you feel better soon.

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