Pernicious Anaemia Society
14,659 members10,436 posts

Low B12, high B9

Apologies if you read this in the Thyroid forum only I didn't realise this group existed! 

I got back my results from Blue Horizon and thankfully thyroid function is good, all is in normal range. But surprisingly my B12 is low at 201 and my B9 (Serum Folate) is high at 45.23. The comments with the results say that the B9 can mask low B12.

I have had GP blood tests in the past and have never been diagnosed as B12 deficient. Could this be because of the masking and I therefore could have been deficient for a number of years? I have been vegetarian for 22 years so this is a big possibility. The reason my GP gave me for my whole list of symptoms (fatigue, zero libido etc.) was put down to a D deficiency (tested at 38) which I am currently on supplements for. But in the 6 months I've been on them I have felt no better, so if I'm honest I'm a little relieved that I have another avenue to explore. Does low vit D have any kind of affect on B9 or B12 levels? Why would my B9 levels be so high?

Also I have my next Dr's appointment in a week's time but want to start B12 supplements now to try and feel better. I understand that I should wait until next week but would the supplements raise the B12 level significantly between now and then or does it take a while?

Many thanks


5 Replies

Difficult to really comment on the B12 and B9 without the reference ranges - there is some variation on results depending on the type of equipment used for the tests.

GP may not recognise the level you have for serum B12 as being low - lot of going too much by test results and not realising there is a large grey range in which people can be highly symptomatic because people just vary a lot in how they use and respond to B12.

Generally the body is really efficient at storing and recycling B12 -  and absorption problems can start slowly - reducing your ability to absorb (and store and recycle) slowly though towards the end when you have used up your reserves things do tend to snowball.

It can take years or even decades for a full blown deficiency to develop.  I had symptoms that I now recognise as B12 deficiency for 40+ years before I was told I had low B12.

The symptoms of b12 deficiency that manifest first also vary a lot from person to person.  Whilst it is also true that high folate masks macrocytosis - that is just one symptom of a B12 deficiency and not necessarily the first.

Being vegetarian may be a factor but if you eat dairy and or fish then you should be getting enough B12 in your diet - if you eat breakfast cereals they tend to be fortified with B12 so you probably are getting enough in your diet and what is going on is a slowly developing absorption problem.

B9 being high can be an indication that you have a methylation problem - that you aren't able to fully process B9 into the methylated forms used at the cell level so it just stays in the blood rather than getting used.  It could also be related to the B12 deficiency as B9 is used in processing and using B12 so if you aren't using B9 for that ...


Thanks for the comprehensive response. The ranges as stated on the test are:

Vitamin B12 L 201 

Deficient <140 pmol/L

Insufficient 140 - 250 

Consider reducing dose >725 

Serum Folate H 45.23 

10.4 - 42.4 nmol/L

Not consuming enough B12 could very much be a possibility. The cereals I do eat are not B12 fortified (I thought they were) and the amount of eggs, milk, yogurt and cheese I eat would put me well under the RDA, again an oversight on my part as I thought I was eating enough. In fact I have increased dairy consumption over the last couple of years and am still under the RDA so may well have not been getting enough B12 for the last 20 years. I have never eaten fish.


If you take RDA then that isn't going to affect the results if you have an absorption problem as amounts are really low compared to what you would need if you have an absorption problem - even a few times RDA is unlikely to make much difference.

1% of B12 is absorbed passively outside the ileum so if there is an absorption problem in the ileum you would need 100x RDA to be getting enough .... and then, because you can't store it you'd probably need a bit more to ensure you have enough - so between 1000 - 1000 mcg is generally quoted as what you need to take - though generally you would try for a format, like sublinguals where some/most is actually being absorbed outside the gut.  

Interesting that your GP seems to be interpreting 'insufficient' as do nothing ... not good.


High levels of folate can mask just one symptom of B12 deficiency - macrocytic anaemia.

B12 deficiency can produce large red blood cells - macrocytic anaemia - which is measured by thinks like MCV - mean cell volume. High levels of folate (or low levels of iron) can mask these effects (folate makes the cells normal, iron deficiency makes cells smaller, and a mix of small and large looks normal).

Other symptoms of B12 deficiency - and measurement of blood levels of B12 aren't masked by high folate.


Another reason for high folate can be bacterial overgrowth - bacteria produce folate. Bacterial overgrowth is likely if you have low stomach acid - which can also lead to B12 deficiency. "Elevation of serum folate is suggestive of small bowel bacterial overgrowth. Indeed, bacterial folate can be absorbed into the circulation. "

Lots of information in this article (quote above taken from 'workup' section):


You may also like...