UK - is it possible to test for low magnesium?

I've read that the normal NHS blood test for magnesium isn't much use because if you have low magnesium, your body will keep your blood levels up by taking magnesium from your bones.

Are there any useful tests that can be done in the UK that NHS doctors would and should take seriously?

 

From what I can see from the Mayo Clinic serum levels do not give a reliable indication of stores but symptoms are unlikely to be due to magnesium deficiency unless serum levels are very low. Most of the stuff about serum levels being unreliable seems to come from commercial supplement sources.

Do you know where you got the information from?

 

Thanks, Jo. Initially, I got that info from a book called (optimistically) The End of Migraines by Alexander Mauskop, who is a professor of clinical neurology at SUNY. He's written about magnesium for migraine in a couple of articles on PubMed, such as this one.

In the book, he says:

Testing for magnesium deficiency is not straightforward. The most commonly done test is the serum magnesium level. Only 1% of the body's magnesium is found in the serum. Most of it is contained in the cells. The uniqueness of our research was that we measured the more accurate ionized magnesium levels. This is a research test and is not available commercially. A test that is available and is more accurate than the serum level, is red blood cell (RBC) magnesium. Even with this test, the level should be at least in the middle of the normal range and not at the bottom of the range.​

I think that since then I've seen similar info about the blood tests elsewhere, but I can't remember where.

 

That looks wrong. The Mg level in serum and cells seems to be similar - about 2meq/L. Intracellular volume may be a bit more than extracellular but not that much. Serum is a relatively small compartment but not that small and anyway the serum size is irrelevant. It is the extracellular compartment that matters.

If that is as wrong as it looks to me - or at least as misleading I would be very sceptical about a physician who writes a book about a subject. like this. Unfortunately, today, medical 'experts' are often those who want to sell a particular story. ME experts are either people who want to sell CBT or autoantibodies. The real experts are the silent majority who don't see a story to sell.

I would be inherently suspicious of someone writing a popular book about nutrition.

 

Yes, and there is a significant issue when dealing with, for instance, people who have just had major surgery for gut problems with fluid imbalance. The serum level may hold up while total body stores deplete.

However, if this really a problem for people with chronic illness at home, without chronic diarrhoea or kidney disease, then even the reviews by the enthusiastic experts would contain something a bit more substantive. The people who seem to write most about this are Ismail, Ismail and Ismail. They write reviews saying how big a problem magnesium is and how unreliable the tests are but with precious little actual evidence of a problem in the general population in wealthy countries.

The Mayo literature suggests that although the tests may need careful interpretation Mg deficiency does not actually cause any problems until the serum level is barn door low.

 

I could not raise my vitamin D levels adequately years ago b/c I was deficient in magnesium. When I corrected the mg deficiency my vittmin D levels went up.

 

The same guy says that not everyone can absorb magnesium via the gut. Certainly I've tried Mg supplement with no benefit but have had big benefits (on migraines) after methods involving absorbing it through the skin.

 

I took magnesium supplements for years early on in my illness but my RBC mg remained very low. I had neurological symptoms similar to parkinsonism and feeling quickly out of breath. I started taking injections and those symptoms went away.

 

I think you could say this about almost anything found in serum.

 

But if that were the case there would be a well known syndrome of magnesium deficiency due to poor absorption - like pernicious anaemia. There isn't as far as I know.

 

According to this paper from the "Clinical Kidney Journal" with the title "Magnesium basics" :

https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC4455825/

In Table 2 it says that 0.3% of the body's magnesium is found in the serum and 0.5% is found in red blood cells. The largest quantity (52.9%) is found in bone.

I take magnesium supplements. Without them I get severe cramp.

 

Yes, looking at various sources the figures are confusing. I was assuming that the original quote was talking about soluble phase magnesium in cellular or extracellular fluids. It looks as if there is a large store in bone matrix which is presumably solid phase so concentration does not really apply.

If serum magnesium is kept up by depleting bone stores, as can occur for calcium then chronic magnesium loss might go unnoticed but it is unlikely to cause any symptoms - other than eventually from bone weakness.

There are quite a lot of sources suggesting that magnesium intake might help bone strength but the most recent reviews still seem to talk in speculative terms. I have not yet seen any formal guideline for magnesium supplementation as a prophylaxis for osteopenia.

 

So maybe the answer to the original question is that what matters is whether or not there is a problem with bone density. Bone density is obviously a concern for those who are housebound and not very active anyway. A DEXA-type bone density scan would indicate whether or not there was a problem - including the possibility of inadequate magnesium stores.

In other words it is not magnesium concentrations that matter but whether or not historically there has been enough in total to maintain bone health.