Pernicious Anaemia Society
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The Connection Between B12 Deficiency and Hypothyroidism (Post 4)

Given that different people have different diets and absorb vitamin and minerals at different rates it is perhaps not surprising that different people experience different outturns from the same circumstances. One size definitely does not fit all. However - I hope there is enough here to draw out some general principles for those seeking to understand why B12 deficiency adversely affects energy levels without even without anaemia. As Sally Pacholok cogently pointed out - it is a primordial molecule at the very root of many biochemical processes. This is but one.


Ref 1

Ref 2 Porth 2005 7th Ed Pathophysiology: Concepts of Altered Health States

Ref 3 Bayliss and Tunbridge 1998 3rd Ed Thyroid Disease: The Facts

Ref 4 Madrid 2009 Vitamin D Prescription: The Healing Power Of the Sun And How It Can Save Your Life

Ref 5 Harvey 2008 We Want Real Food: The Local Food Lovers Bible

6 Replies

Sorry but there are several reasons why B12 would cause exhaustion without anaemia and without thyroid problems - one that springs to mind is the role B12 plays in the process used to release energy in cells.

I am not denying that there is a link between healthy operation of the thyroid and B12 but it is also true that autoimmune thyroid problems are often concurrent with autoimmune B12 problems - same is due of other autoimmune conditions because there are several autoimmune conditions going on at the same time. This may be down to the fact that people tend to have several auto-immune conditions if they have one.

In the case of some conditions - such as diabetes - which may not be autoimmune - it may be interactions between drugs used to treat diabetes and B12 absorption.

To point just to thyroid is potentially misleading.

Diabetes will also lead to extreme tiredness because of the effect on processing of one of the key building blocks in energy production.

There is a huge overlap in the symptoms of many of these conditions which is going to make a thorough diagnosis difficult.

To be honest I didn't find having 4 posts on this subject helpful. In future if you need to post in multiple parts I would suggest that you do this by 'replying' in a single post.


I thought the 'primordial molecule' mentioned in the post (above the references) referred to the mitochondria in all our cells are often called the energy powerhouses because they are responsible for energy in the cells and in the body? I was under the impression they responded to more than the thyroid?

They have different dna to the rest of the body - perhaps why, during these polluted times we have such problems appropriately communicating with the aliens in our bodies?


A primordial molecule is a chemical molecule that arose very early in evolution. Mitochondria are organelles within the cell that burn fuel to produce the energy molecule ATP (adenosine triphosphate) that powers all cell actions. This process needs B12 to happen properly. No B12 means the cells operate at low efficiency - hence tiredness (among other things). The mitochondria do indeed have their own DNA. It is thought that they originally were bacteria that got incorporated into our cells because they are so very useful and efficient at producing energy - so you are not very wide of the mark when you say they are "alien". Mitochondrial DNA is handed down exclusively from mother to offspring. Fathers only contribute to nuclear DNA. There is an exceedingly complex interplay between the mitochondrial DNA and the nuclear DNA - but this is part of another story and beyond the remit of this site.


Did you mean to post this on the Thyroid UK forum as I feel I've missed the point of what you are trying to convey.

Are you saying that a B12 deficiency causes an under active thyroid and that the fatigue is actually the result of that rather than a B12 defiency.

Could you please clarify.


Everything is connected. A division between systems is inherently an artificial distinction. B12 deficiency can cause Hypothyroidism by reducing Thyroid Stimulating Hormone (TSH). B12 is needed to create TSH. If TSH goes low, the thyroid will make less thyroid hormone (thyroxine). Low thyroid hormones cause tiredness (among other things). B12 can also cause tiredness directly as it is needed in energy production within the cells. I posted because low thyroxine and B12 deficiency often go hand in hand. If you have one you need to watch out for the other.

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I agree that low thyroid function and low b12 levels can go hand in hand. There are different reasons for the cause of each illness.

Not all who have an under active thyroid (UAT) have a B12 deficiency and not all who have B12 deficiency have an underactive thyroid.

Low TSH doesn't cause hypothyroidism. Hypothyroidism is the reason for TSH production by the pituitary gland.

A high TSH with low FT4 & FT3 is indicative of hypothyroidism. If TSH is suppressed with high FT4/FT3 this shows possible hyperthyroidism

90% of UAT sufferers have autoimmune antibodies (hashimotos) which attack and destroy the Thyroid. The more it is destroyed the less thyroid hormone (FT4/FT3) produced. The pituitary will then produce thyroid stimulating hormone (TSH).

If the Thyroid is working normally the TSH will be low and there is no need for the pituitary to get involved. Levothyroxine will normally reduce TSH levels and levels of 1 or under are considered optimal but testing of FT4 and FT3 should always be carried out.

FT4 is a storage hormone that needs to be converted into the active hormone FT3. A small amount can be converted by the Thyroid itself and although the majority is converted by the liver it also happens in the kidneys and the brain. Some have a DIO2 polymorphism which prevents conversion so no amount of levothyroxine will help and at this point T3 (liothyrinine) needs to be substituted. T3 only replacement will suppress TSH, FT4 will also be very low as the storage hormone is not required.

I have had Hashimotos symptoms for the last 25 years but have only had a problem with low B12 for about a year. I tested positive for intrinsic factor antibodies 10 months ago and got my diagnosis of Pernicious Anaemia. It is fair to say that there are common shared symptons between them but they are quite different diseases. There are subtle differences in the type of fatigue experienced from both conditions. I am more inclined to say that in my case the pernicious anaemia was exacerbated by my autoimmune hypothyroidism.

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