The number of times I see magnesium tested using serum and it is ‘normal’ drives me mad. It can be very misleading and doesn’t really reflect levels in your system at all. I have always recommended red blood cell (erythrocyte) testing – and it seems researchers in an article in Nutrients agree.

I find magnesium chronically low in many people – especially those with fatigue, stress and the ‘syndromes’ such as CFS, fibromyalgia, MCAS etc. You can read my Magnesium factsheet here for more general info on it. Meantime, here’s the article:

Magnesium: Are We Consuming Enough?

In chronic latent magnesium deficiency, magnesium levels in the blood are within a normal range, despite there being severely depleted magnesium content in the tissues and bones. Therefore, using magnesium levels in the blood to determine total magnesium levels in the body can result in underestimation of magnesium deficiency in healthy and diseased populations. Recent studies have shown that individuals with serum magnesium levels around 1.82 mg/dL (0.75 mmol/L) are most likely to have a magnesium deficiency, while those with serum magnesium level more than 2.07 mg/dL (0.85 mmol/L) are most likely to have adequate levels [20,21]. Of relevance, individuals with serum magnesium levels between the 0.75 to 0.85 mmol/L should be tested with additional measurements to confirm body magnesium status.

In humans, red blood cell (RBC) magnesium levels often provide a better reflection of body magnesium status than blood magnesium levels. 

The researchers go on to detail why magnesium is so important:

Magnesium deficiency can induce a wide range of clinical complications, including painful muscle spasms, fibromyalgia, arrhythmia, osteoporosis and migraines.

They also point out that sufficient Vitamin D – which I also find chronically low in many people – is also needed for magnesium absorption. This is another one often designated ‘normal’ when it isn’t! See my Vitamin D factsheet here.

Nice to see it set out so well here. Moral of the story: check your magnesium and check it the right way. Viva do a RBC magnesium test, which you can get here. They also do a Vitamin D test via blood or fingerprick. Both of those can make SUCH a difference to how you feel so don’t miss them or be misled by poor testing or too-low ‘normal’ levels being applied!