B12 and Magnesium

After reading the post by Steve101 on this subject a month ago, I was so intrigued that I decided to seek a medical opinion. Like many people who have had an oesophagectomy, I sometimes suffer from fatigue and a general lack of energy.

I forwarded the post to the Chairman of our local Upper GI Network Cancer Group, on which I am a patient representative. He forwarded it on to the Upper GI Dietitian at Watford General. Here is her response. I have edited it slightly and, therefore, take full responsibility for any errors.


“I read the post with great interest and in answer to your question is this true? Well, mostly yes!

Anyone having undergone upper GI surgery has multiple reasons for developing nutritional deficiencies, e.g. poor food intake, post-op therapy, surgical stress, etc. As regards magnesium, it has many roles in the body and I would agree that many people are deficient, particularly those who have had bowel surgery. Gastro-intestinal absorption is indeed poor and hence we supplement it intravenously. As for the ‘uselessness’ of serum measures, I don’t know the answer to this, but can say that we frequently check and correct patient levels and the serum levels respond quickly to intervention. In addition, I am not convinced of the absorption through the skin and it’s certainly new to the rest of the team. However, magnesium has a very low toxicity, so I wouldn’t worry about its safe use by patients.

B12, again like most wonderful nutrients, has multiple roles in the body. Those proven to be at risk are gastrectomy patients, due to the lack of intrinsic factor, and all gastrectomy patients’ GPs are specifically advised to give B12 injections at 3-6 month intervals, but any upper GI patient is also nutritionally at risk as mentioned above. Again, it can be safely supplemented and can be taken orally.

In answer to your question about how we manage these issues locally, I personally recommend (by letter) to all upper GI patients’ GPs that a broad set of micronutrients are checked annually (i.e. full blood count with haematinic markers (ferritin, B12 and folate), liver function tests, parathyroid hormone level, zinc and selenium levels) and I also suggest a daily multivitamin. I do not give more specific advice to patients for a couple of reasons: 1) many patients cannot absorb this level of information and there is really a limitless quantity that they could read; and 2) unfortunately the scientific evidence for micronutrients in this patient group is lacking. There is a huge amount of theory, but demonstrating deficiency in large numbers is inherently difficult. My recommendation of a multivitamin is preventative, based on recent research by dietitian Stephanie Wakefield at St. Mary’s Hospital in London.

In summary, I would definitely agree that this patient group is at risk, but would add that it is not just Mg and B12, but probably other micronutrients as well, and a daily broad spectrum multivitamin should cover all bases. Most nutrients will be absorbed well, but you will get some benefit even from those that are poorly absorbed. “


Some of you may have attended, as I did, the excellent lecture that Stephanie Wakefield gave to the London Branch of the OPA a few years ago on the prevalence of micronutrient deficiencies in upper gastro-intestinal cancer patients after treatment. In summary, the recommendations are to get a broad set of micronutrients checked annually by your GP and take a daily broad spectrum multivitamin supplement.

Hope this is useful.


11 Replies

  • That's very interesting advice. I get very tired after meals on occasion and my surgeon advises that I try either Dextrose or a glass of water ; to see which might work. I don't have a general feeling of fatigue but I may start taking some multivitamins anyway.

    Please thank the nurse for that we'll written and clear note.

  • Hello Spikey,

    I can't remember seeing the original post (so it may have been covered there), but one further factor is that long-term PPI use (>3 months) has been associated with low circulating Mg levels - so a double whammy really. You mention the association between low Mg and fatigue but another interesting point that I learned a while back is that low Mg is also associated with depression and particularly agitated depression - Mg has been used to good effect in treating this condition in some patients, particularly in the US. I take a multi-vit/mineral tablet daily and that provides 27% of daily Mg needs - there's a good chance I get the rest through food but I also occassionally take a specific Mg supplement as a belt and braces strategy.

    Thanks for your interesting post and to Steve 101 for bringing this up.


  • Thank you - that is very helpful! And our thanks to your dietician as well.

    For those who are interested, there are notes from Stephanie's talk on the OPA website here: opa.org.uk/resources.html

    Stephanie did some research that did clarify that patients can suffer from malnourishment after an oesophagectomy / gastrectomy - it does not mean that it is compulsory to suffer that way - some don't; but others may, so it is definitely worth bearing in mind!

  • As a patient living in the US, is it possible to get a copy of the letter that is referenced in the piece as being sent to patients' GPs? I would be greatly interested in what is considered routine nutritional testing in this population. Thanks in advance. \wc

  • Chris,

    I will ask for a copy and message it to you.


  • Hello all

    I'm pleased to see my original post has raised so much interest.

    I would recommend that anybody who wants to know more about magnesium read the book ' The magnesium miracle'. The book is not written by a "quack" but everything in the book is fully evidenced.

    Fact - the magnesium serum level is next to useless, it tells you very little.

    Fact - to absorbe magnesium from the stomach you need it to be acidic. Fact - if you are on PPI's you won't have an acidic stomach.

    Fact - you can absorbe magnesium through the skin.

    Fact - magnesium has a key role to play in literally hundreds of metabolic processes. Including energy cycle and allowing muscles to relax.

    Fact - you can't overdose on magnesium you will just excrete it and have loose bowels

    Read the book. Give it a try, you have nothing to loose, but it might just help you!

    Look for magnesium oil, available from Amazon, about £9 for a 100ml spray bottle.

    Best wishes to all of you.


  • Hello Steve,

    I don't believe your point above regarding PPIs and their effect on stomach acid is true. My understanding from the scientific literature (the actual studies) is that PPIs don't completely switch off acid production and that the acid environment of the stomach is maintained over a 24-hour period of dose administration. They do however significantly increase pH (reduce acidity). Many years ago a certain drug company tried going down the road of developing a proton pump blocker (as opposed to inhibitor) which resulted in unmanageable diarrhoea, and which they concluded was the result of completely switching off the proton pump. Hence the rationale for maintaining some acidity. The stomach should therefore be acidic with PPIs and should therefore be capable of absorbing magnesium given in tablet form by mouth.

    All the best,


  • Hello David

    Thanks for your post and the clarification on how PPI's work.

    The book 'The Magnesium Miracle' (which is fully evidenced) specifically refers to PPI's and their impact on magnesium absorption. My understanding having read 'The Magnesium Miracle' is such is the impact of PPI's in reducing stomach acidity (increasing PH) is that this will impact significantly on magnesium absorption.

    You are obviously someone that has an interest in these sort of issues, I really recommend you read The Magnesium Miracle as it is a fascinating read, it opened my eyes.

    This is a fantastic site for sharing information.



  • Thanks for clarifying Steve, that does makle sense if it was reduced acidity (as opposed to no acidity). I'll try to get a copy to read.

    All the best,


  • Hello David

    Can get it at Amazon.


  • this magnesium serum level, is a bit of a red herring,although it is a useful piece of information it is somewhat misleading,red cell magnesium levels are the gold standard and are the only real measure of accuracy regarding this vital mineral.i worked in a hospital lab and this was the general opinion held by all the senior staff,however even consultants and drs and dieticians,nurses etc did'nt really grasp this.this is not a slur on them it just seems to have slipped under the radar,and it's not the only test that this is true of