Thyroid UK
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MTHFR / Methylation Pathway Testing & B12 Query

Hi All

Firstly thanks again to everyone who kindly took the time to respond with help and advice to my first post here last week.

In summary for people who haven't read that post or thread: I was diagnosed with hashimotos hypothroid almost 2 years ago, coeliac disease soon after. I have positive parietal cell antibodies and generally things seem to be pointing to B12 defiency/PA. Im 100% gluten free and taking levothyroxine but feeling more exhausted than ever. Have lost my job, am unable to go out for more than a couple of hours (and even then feeling awful) and I want my life back.

I have put together an action plan on the back of my reading, research, informal discussions with a nutritionist, a lab testing company and other knowledgeable people along with all the comments from the lovely people from here and PA forum last week.

Unfortunately part 1 of my plan has failed already! I contacted my endo to ask for his authorisation for B12 injections. I mentioned some of the things that forum member Polaris and others had mentioned that Docs should do even if tests show normal levels, if patient still exhibits symptoms. This was his response:

"I do believe that B12 levels can appear normal when someone is truly deficient. However it is difficult to sanction treatment or ask your GP to kindly administer this when the results look “okay” as they may not feel comfortable prescribing under those circumstance. Secondly I mentioned in the past methylation pathway defect tests – if these are abnormal then the type of B12 you require may be just as important – too much or the wrong type of B12 and/or both can cause more problems. Therefore suggest working through the problem with Nutritionist with results may be best solution."

Now I have mentioned these B12 injections to him previously also. So I do not wish to push the point with him as he has generally been quite helpful and empathetic. However I need to take some action, hence the plan I wrote at the weekend.

MTHFR testing is one of the points on my plan.

So my questions here are:

1) re the Endo's letter above - I did not realise there were different types of B12 that I could take! Could anyone shed any light on this? And re: "too much" B12 - I thought that the body just discharges what it doesn't need?

2) Methylation pathway testing. I looked into this a lot last week and have found a couple of companies that do genetic testing. I have found it gets very very complicated! One site I found though seemed simple enough "23andme". Has anyway any experience of using them? If so is it possible to just find out what is going on with my thyroid and any vitamin/mineral defiencies? i.e I want to find out what is wrong with me now so that I can work on fixing it, and not get a load of data telling me I might have heart disease in the future!

Apologies if that doesn't all sound thyroid related, but I do believe it is linked in many ways. I hope those questions make sense, and would be grateful for any helpful advice. Thanks for reading.


13 Replies

For the effects of excess B12, see the site:

Overdose Effects. Some of the symptoms of vitamin B12 overdose include itchiness on different body parts and numbness, improper heart functioning, giddiness etc

For discussion and showing different B12 derivatives se:

Cobalamin - Wikipedia, the free encyclopedia

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That's great thank you for your help and the links. Some interesting information there.

It seems that the Endo may be right in finding out some more info on my B12 status prior to commencing with injections.


A bit worrying Diogenes as most postures on the subject reckon excess B12 is excreted in urine and I have repeated their wisdom which may be questionable! I am taking 5000 mcg a day as I was low in the range and feel much better for it but is it doing damage for the future?

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Do remember, though, that gigantic doses are regularly given to counter the effects of smoke inhalation. When I say gigantic, I mean it. FIVE GRAMS - when the actual daily requirement is less than a millionth of that.

Of course, that is not the same as taking B12 every day. And there can be side effects at that level. But there are few medicines which could ever be tolerated at that sort of overdose.


Thanks,led me to check and edit it was 5000 mcg not mg


I didn't even notice! Have become far too used to "reading past" the milligram/microgram mistakes which happen so frequently.

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I would think if you feel so well on it must need it..! !



Maybe Flower,but perhaps I should reduce the dose looking at the table on Diogenes post. Ideally would like regular blood checks for levels but will only happen if use private labs.


Hi Treepie

Do you mind if I ask how you came about that dosage? Was it trial and error yourself and buying through the internet, or was it prescribed and administered by Docs?


Hi Lee, GP said take no vitamins! I had seen lots of advice on here about starting at 5000 mcg and then after a few months reducing to 1000mcg. My B.12 was low in the range.

I purchased on Internet and began with 5000 but felt nauseous so I took 2500 and then decided to take that in the morning and another 2500 at bedtime.

That was ok. I get some more in multivitamins I take so I am going to try out 2500 a day of the Jarrows.

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Hello Lee,

I had the Genova Diagnostic MFTHR test.

It proved I had a 50 - 60% risk of methylation impairment.

Although I have always had a high B12 serum blood, I was advised I could still be deficient as the cell receptors could be blocked.

I undertook the B12 active test available in link below but this also was came back with a high result.

My nutritionist was insistent that I supplement as I suffer neuropathy on feet and sometimes hands, a sour taste in my mouth and excessive thirst.

She had recommended a B Complex by Seeking Health put together by Dr Ben Lynch who is at the forefront of B12 deficiency and MTHFR. It contains the active form of folate and B12. I supplement sometimes as am now very confused as to whether I should be supplementing or not as neuropathy can be a symptom of too much B12.... ! ! !

A good site recommended to me by another member is (Dr Ben Lynch)

I would also highly recommend the Cyrex Array Gluten Associated Cross Reactive Foods blood test to see what foods you are intolerant to. Cutting out gluten is a start but I found I was also completely intolerant to amaranth and rye and other gluten free grains.

I also undertook the Detoxigenomic Profile which I believe to be similar to the "23andme" test that other members have done but more comprehensive.


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Hi Flower

Was that done through a Nutritionist? I've spoken with Genova and they won't let me do any "genomic" testing without proof of qualifications in the field.

I will check out Ben Lynch, thank you. I have seen his name crop up in a few articles actually now you mention it.

So you are taking an oral B12 supplment? How are you feeling now? I hope you are feeling well.

I will check out that detoxigenomic test, thank you.

That's a good idea to check other foods that I'm intolerant too. Obviously I'm gluten free 100% now, but I do know that I still have an issue with lactose unfortunately (severe bloating straight after eating ice cream, custard etc, bad tum the next morning) but I think there are other food groups I'm eating that are perhaps stopping my gut from healing. The tests are really expensive for this though sadly so I'm having to pick and choose with these private tests at the moment.

I am tempted by the 23andMe test though. Just hope it can point me in the right direction for my thyroid and gut issues and vitamin deficiencies.

Thanks again



I think...(but am not sure) ..the 23andme test includes the MTHFR.

Others members will be able to confirm this.

I had all my tests done through a nutritionist.


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