Magnesium Gets a Makeover! A Brand New Biomarker & Better Optimization

Discover the latest in magnesium research with our brand new biomarker and optimization techniques. Stay informed and optimize your health today!

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By Staff Writer

Updated June 12, 2024.

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We’re thrilled to announce the newest addition to our Ultimate Panel biomarker family: RBC Magnesium! Never heard of it? Most people haven’t, but that doesn’t mean it’s any less important.

Magnesium is an essential mineral that needs to be supplied in the diet, and RBC Magnesium measures the levels of magnesium inside of your red blood cells. In this blog post, we’ll delve into the science behind why that measurement is important, and how it’s different from the standard Serum Magnesium measurement you’re used to seeing. We’ll also discuss our new and improved optimal range for the existing Serum Magnesium marker.

a cell phone with the text better sleep checklist on it

First, here’s a primer on magnesium in general, outlining the critical roles it plays in your health, well-being and performance. It’s a hefty dose of learning, but we’re pretty sure you’ll find it fascinating. (If you’re a science maverick and don’t need the biology lesson, feel free to skip straight to the RBC Magnesium and new Serum Magnesium range sections).

Magnesium 101

Walk into your local supplement store, and you’re bound to find at least one shelf lined with a variety of magnesium supplements. Magnesium is popular for a reason: it’s one of the most important minerals in your body.

It plays especially important roles in maintaining healthy and nimble muscles, well-functioning kidneys, and a well-tuned heart – things you want working well if you’re trying to achieve performance goals, or just improve your overall health. All of these (and many other) functions are due in large part to magnesium’s role as a key cofactor in over 300 different metabolic reactions, including protein and DNA synthesis.2,3,4

a diagram showing the benefits of biomarker breakdown

Magnesium also happens to be one of the most abundant minerals found throughout the body, as it is used by every single one of the organs. But just because it’s important and abundant, doesn’t mean everybody has enough of it. Not surprisingly, magnesium deficiency has been associated with a slew of symptoms and – when the deficiency is more serious – diseases.  

Some of the more mild deficiencies may result in seemingly accidental symptoms like eye and muscle twitches or spasms, anxiety or irritability, and difficulty falling asleep.  More severe cases are associated with conditions like heart disease and abnormal heart rhythms, hypertension, glucose regulation, as well as high levels of inflammation, to name just a few.2,3,4

Since magnesium is also critical in creating energy in the body (high school biology flashback: magnesium activates adenosine triphosphate, or ATP), it is crucial for maintaining cardiorespiratory fitness in athletes. Increased intake of dietary magnesium has been shown to benefit athletic performance by improving the efficiency of working muscles.2 And you don’t need to be in the pro leagues to reap the fitness rewards!

The best measure of magnesium

We all want to be as accurate as possible when testing the body for critical markers. But sometimes, the most scientifically precise means of measurement aren’t the most realistic or convenient (spinal tap, anyone?). There are a few ways to accurately assess total body magnesium that are not user-friendly or require specialized equipment not available in most blood testing labs.5

For example, the “gold standard” magnesium loading test requires a person to collect their urine over a 24-hour period after receiving a magnesium sulfate injection at a doctor’s office. Carrying around a jug of urine in the office isn’t exactly the picture of convenience. Ionized Magnesium, another measurement, is a user-friendly and highly accurate blood test that is simply not widely available.

The two most readily available tests – and the ones that InsideTracker uses to assess your total body magnesium – are the Serum Magnesium and RBC Magnesium tests, both of which, while imperfect, are still incredibly useful to people interested in optimizing their health. Together, they make up the new Magnesium Group on a user's bloodwork page.

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Battle of the biomarkers: Serum Magnesium vs RBC Magnesium

Serum Magnesium

The most widely used method of determining whether someone is magnesium-deficient is measuring Serum Magnesium. "Serum" is the blood plasma – the clearish part of your blood that is neither a blood cell nor a clotting factor. Chances are, long before you ever tested with InsideTracker, you saw this biomarker listed among your annual physical blood test results. However, Serum Magnesium is actually far from being the best available measurement.

Why not? Simply put, in its “as-is” clinical reference range state, Serum Magnesium has shown to be the least sensitive of the measurement methods, and importantly, it does not correlate with tissue levels or total body content of the mineral.3,5 Meaning: your body might not actually have access to the amount of this critical mineral that it needs. In fact, if you are “low normal” in the current Serum Magnesium reference range, your actual total body magnesium may be far too low for health, let alone optimized health!

The reasons for Serum Magnesium’s relative inefficiency as a measurement can be summarized simply in two points:

  1. The way magnesium is metabolized in the body – while 50% of total body magnesium is stored in the bone and tissue, only 0.3% is present in blood serum! And as serum magnesium decreases, the body pulls magnesium out of red blood cells in the bone and tissue, in order to compensate for that decrease. So, serum magnesium can test as “normal” even when critical levels in the bone and tissue are decreasing.
  2. The current reference range – the current reference range for “normal” Serum Magnesium levels was established back in the 1970s and likely included many individuals with an inadequate intake of the mineral for an extended period of time. This, at the very least, is thought to have shifted the bottom of the range below what is considered healthy. That’s why we’ve just updated our own optimal range for optimal Serum Magnesium – more on that later!

RBC Magnesium

Cue applause: Welcome our newest biomarker, RBC Magnesium! As the name suggests, this test measures the magnesium concentration of your red blood cells (RBC), which is about 3 times higher than it is in your serum. The reason this test is more sensitive in revealing magnesium deficiency is because, as your body’s serum magnesium level decreases the body reacts by leaching the mineral out of stores in your red blood cells, where it’s more abundant, in order to replenish serum levels. It’s like the old adage of “borrowing from Peter to pay Paul” – not a beneficial outcome.

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In fact, studies do show that long-term, low-magnesium diets result in lower content of the mineral in red blood cells, and that magnesium supplementation improves RBC Magnesium content while having no effect on serum magnesium in those who are deficient – such as diabetics, obese people, and migraine sufferers.5

It is well known that magnesium is important in modulating blood pressure, has a positive effect on migraine headaches, insulin sensitivity, and chronic inflammation.3 RBC Magnesium has proved to be a superior biomarker relative to Serum in identifying some of these conditions. When magnesium supplements were used to increase the reduced RBC magnesium level, results point to a reduction of inflammation, high blood pressure, and improving insulin sensitivity.7,8,9

So, why doesn’t everyone use the RBC Magnesium test? Unfortunately, since the medical field has historically put pretty much all its eggs into the the Serum Magnesium basket, not as much is known about what may constitute an optimal range for RBC magnesium. However, similar to Serum Magnesium, there is evidence to suggest that the current clinical reference range may be too wide to use if one wants to achieve the goal of optimal health (as opposed to just disease avoidance).

Your Serum Magnesium makeover: A whole new range

Serum Magnesium is moving on up… or at least, its optimal range is. Recently, InsideTracker scientists reviewed our existing optimal ranges (you know, the “in the green” everyone loves to see) for Serum Magnesium. Based on that review, they determined that it was necessary to update InsideTracker’s minimum optimal level. As we mentioned earlier, the reference ranges for Serum Magnesium were established way back in the 1970's – and new, peer-reviewed studies show that people with levels that fall within a specific portion of those ranges, were 50% more likely to develop impaired fasting glucose and type 2 diabetes! Not only is that sub-optimal, it’s downright risky.  It was time for a change.

This change means that 1000+ InsideTracker users may drop out of the green, and go from having optimized magnesium to being normal but below optimal – in InsideTracker lingo, the yellow “needs work” category.  So, don’t be surprised if you're an InsideTracker user who soon finds themselves logging in to their account and seeing a whole new set of “magnesium-rich foods” recommendations in order to address a less-than-optimal Serum Magnesium result!

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A user's old Serum Magnesium results versus new results with customized optimal zone.

Curious to see where you fall? If you’re an existing InsideTracker user, your Serum Magnesium results have been updated! Log in to see if your recommendations have changed. If you’re not yet part of the InsideTracker family, purchase an Ultimate test to see if both your RBC Magnesium and Serum Magnesium are optimized. 

Summing it all up

It should be clear by now that magnesium status assessment is tricky business, and the available tests are a balance between user-friendliness and accuracy. The Serum Magnesium test is well established, quick and easy to measure, though it’s not the most sensitive in detecting actual deficiency. However, we’ve just beefed up the test’s utility significantly by updating the optimal range, as well as working on a (soon-to-come!) individualized genetic profile.

RBC Magnesium, the other easy-to-measure biomarker for magnesium status, is now included in our Ultimate Panel for those who would like to see an additional, more sensitive, measure of magnesium deficiency. Together with Serum Magnesium, Ultimate Panel users will find a brand new Magnesium Group on their bloodwork page, containing both biomarkers and even more precise nutrition recommendations for optimizing levels.

In fact, it’s been recommended by experts that two markers of magnesium status may offer more reliable results than one alone.(3) That’s why we’re offering exactly that – and based on our preliminary estimates, it’ll provide opportunity to further optimize health for over 1,000 of our current users…and everyone else to come!


[2] H. C. Lukaski, “Magnesium, zinc, and chromium nutrition and athletic performance.,” Can. J. Appl. Physiol. = Rev. Can. Physiol. Appl., vol. 26 Suppl, pp. S13-22, 2001.

[3] S. L. Volpe, “Magnesium in Disease Prevention and Overall Health,” Adv. Nutr. An Int. Rev. J., vol. 4, no. 3, p. 378S–383S, May 2013.

[4] University of Maryland Medical Center (

[5] M. J. Arnaud, “Update on the assessment of magnesium status.,” Br. J. Nutr., vol. 99 Suppl 3, no. S3, pp. S24-36, 2008.

[7]  W. Engelen, A. Bouten, I. De Leeuw, and C. De Block, “Are low magnesium levels in type 1 diabetes associated with electromyographical signs of polyneuropathy?,” Magnes. Res., vol. 13, no. 3, pp. 197–203, Sep. 2000.

[8]  F. Corica, A. Allegra, R. Ientile, and M. Buemi, “Magnesium concentrations in plasma, erythrocytes, and platelets in hypertensive and normotensive obese patients.,” Am. J. Hypertens., vol. 10, no. 11, pp. 1311–3, Nov. 1997.

[9]Clin Chim Acta. 2000 May;295(1-2):63-75.

[10]  K. Sudhakar, M. Sujatha, V. B. Rao, A. Jyothy, and P. P. Reddy, “Serum and erythrocyte magnesium levels in hypertensives and their first degree relatives.,” J. Indian Med. Assoc., vol. 97, no. 6, pp. 211–3, Jun. 1999.

[11] Y. Li, A. Ma, Y. Sun, H. Liang, Q. Wang, X. Yi, and X. Han, “Magnesium status and dietary intake of mid-old people in a rural area of China.,” Magnes. Res., vol. 22, no. 2, pp. 66–71, Jun. 2009.

[12] Lancet. 1991 Mar 30;337(8744):757-60.