Minerals and trace elements: which blood values give insight?

A single tube of your blood holds less than a teaspoon of minerals. That small amount still helps decide whether your heart beats regularly, whether your muscles relax and whether your nerves pass their signals along. Potassium, sodium and calcium sit inside every heartbeat you take today.

Here is the part you rarely hear: blood measures some minerals very well and others quite badly. Potassium, sodium and calcium are read reliably. Serum magnesium and zinc say far less than most test sellers suggest. That distinction is the difference between a useful result and an expensive number.

I am writing this because I dislike how often it goes unsaid. Selling a mineral panel is easy. Telling you what it cannot see is more honest. Below you will find, per mineral, what your blood does and does not show, and the individual values are covered in separate articles.

What are minerals and trace elements?

Minerals are inorganic substances your body cannot make. You get them from food and drink. Trace elements are the same thing, except you need far less of them, often under 100 milligrams a day.

So the distinction is about quantity, not importance. You need roughly 3,500 milligrams of potassium a day and around 9 milligrams of zinc. A shortage of the second is not less serious because the number is smaller.

The main minerals are calcium, potassium, sodium, magnesium, phosphate and chloride. The best known trace elements are iron, zinc, selenium, copper and iodine. The Dutch Voedingscentrum files them all under one heading: substances that reach you through your plate.

Vitamins sit outside this list. They are organic and behave differently. If that is where you are heading, read on about vitamin deficiency and which vitamins to test.

Which minerals can you measure in blood?

Almost all minerals are technically measurable in blood. The real question is whether that number means anything. For potassium, sodium and calcium the answer is yes. For magnesium, zinc and iodine it is more nuanced, because your blood only shows a fraction of your total store.

This table is the heart of the article. It sums up what your blood really tells you per mineral, and when measuring adds something.

For the detail per value, separate articles go deeper. Read on about your potassium value, about calcium in your blood or about low sodium.

Which minerals does blood measure well, and which not?

Blood measures a mineral well when the body regulates that substance in the blood itself. Potassium, sodium and calcium qualify. It measures a mineral badly when the store sits mainly in your bones or cells. The blood number then stays normal while the store falls. Magnesium is the classic example.

Take magnesium. Under 1 percent of your total magnesium sits in your blood; the rest is in bone and cells. Your body keeps that blood number steady at almost any cost, pulling magnesium from bone if it has to. A normal serum value therefore does not rule out a shortage in your tissues. Researchers have argued for years that the serum magnesium reference interval deserves revision, for exactly this reason (Costello 2016, PMID 28140318).

That is why Vitalcheck offers intracellular magnesium alongside serum magnesium. The second measures magnesium inside your red blood cells and lands closer to your actual store. It is not a perfect measure, but it is a more honest one.

Zinc has a different problem. Serum zinc falls during inflammation, even when your intake is fine. During a strong inflammatory response, plasma concentrations of several micronutrients can drop sharply without any change in diet (Duncan 2012, PMID 22158726). A zinc value without an inflammation marker beside it can quietly mislead you.

Which supplements do I actually need?

There is no general answer, and that is the point. Anyone who starts swallowing without measuring is guessing. The Dutch Gezondheidsraad keeps it short: on a varied diet, most people in the Netherlands get enough minerals. Vitamin D is the well known exception, and it is not on this list.

Imagine two people who are both tired, one with a ferritin of 8 micrograms per litre and the other with 95. The same supplement might help the first. It will certainly not help the second. Without measuring, you simply cannot see that difference.

My own position, and not everyone will agree: for most healthy people a multivitamin with minerals is an expensive form of reassurance. Measuring what is actually going on is cheaper and more precise than swallowing broadly. Always discuss a result with your GP before changing anything.

If you want to know where minerals come from, the route via your plate is almost always first. Bananas, potatoes and pulses deliver potassium. Dairy and leafy greens deliver calcium. Nuts, wholegrains and shellfish deliver zinc. There is more on this in nutrition and your blood values.

Why do some people absorb minerals less well?

Because absorption is not about how much sits on your plate but about how much your gut lets through. Substances in your food can bind minerals, medication can block uptake, and a gut condition can disturb the whole process. Two people on exactly the same diet can therefore end up with different blood values.

The best known example is phytate, a compound found naturally in grains, nuts and pulses. Phytates bind zinc and iron in your gut, so you absorb less of them. That is precisely why people eating fully plant-based need more zinc than average to arrive at the same place.

Medication matters too. Stomach acid inhibitors lower the acidity in your stomach, and that acid is exactly what is needed to release some minerals from your food. With prolonged use, that can affect the uptake of magnesium among others. Diuretics work from the other side: they increase excretion through your kidneys.

That is why I always look at the complete picture. A low value in someone who has taken acid inhibitors for years means something different from the same value in someone taking nothing. What you swallow belongs with your result.

How do you recognise a mineral shortage?

Early shortages are quiet. They produce vague complaints that fit dozens of other things: fatigue, muscle cramp, poor concentration, palpitations. Precisely because those complaints are so unspecific, a blood value can help point a direction, or rule a suspicion out.

Muscle cramp shows how misleading this gets. Cramp is almost automatically pinned on magnesium. In practice it can just as easily come from potassium, from dehydration, or from simply training too hard. The assumption is popular; the evidence is thin.

What strikes me about the results I see pass by: people hunt for the one number that explains everything. That number rarely exists. A pattern across several values almost always says more than a single deviation.

Picture someone on diuretics for high blood pressure who has been tired for weeks. In that person a potassium of 3.2 mmol/l is not a coincidence but a logical side effect. Context decides what a number means. See also reference ranges explained.

What can distort a result?

More than you would think, and this is the part that appears almost nowhere. A mineral result can shift because of the blood draw itself, or because of your albumin. An inflammation that has nothing to do with minerals can move it too. That is how an abnormal number appears in a body that is perfectly balanced.

The best known is haemolysis. If red blood cells are damaged during or after the draw, potassium leaks out of those cells into the serum. The result then reads too high while nothing is wrong with you. Errors in potassium results from such pre-analytical causes are well described in the laboratory literature (Schlueter 2023, PMID 37042478). With an unexpectedly high potassium, a repeat draw is often the logical step.

With calcium, albumin is the issue. Roughly half your calcium travels bound to the protein albumin. If your albumin falls, your total calcium falls with it while the active portion stays the same. That is why labs work with a corrected calcium value, an idea described as far back as 1973 (Payne 1973, PMID 4758544).

And as we saw above: inflammation pushes zinc down. Three different mechanisms, three ways a number can mislead you. Anyone unaware of them draws conclusions too fast.

When is measuring worthwhile, and when not?

Measuring is worthwhile when the result could change what you do. With symptoms, with medication that affects minerals, or with a diet that misses a whole food group. Measuring adds little if you have no complaints, eat varied, and there is nothing you would adjust based on the number.

That sounds strict coming from a company that sells blood tests. It is still the most honest line I can draw. A value that leads nowhere is noise.

These are the situations where a mineral measurement often does deliver something:

• You take diuretics, laxatives, stomach acid inhibitors or lithium.
• You have had prolonged vomiting or diarrhoea.
• You eat fully plant-based or leave out whole food groups.
• You have gut complaints or a condition affecting absorption.
• You have palpitations, muscle weakness or unexplained confusion.

If you recognise yourself here, you can have an extended health checkup at Vitalcheck without a referral, which includes several minerals. Take the result to your GP and decide there what is needed. One abnormal value is the start of a conversation, not a conclusion.

One last thing I want to pass on. A mineral that is low today need not be low in three months, because your values move with what you eat, drink and swallow. A second measurement after a while therefore often says more than a single snapshot, certainly if you have adjusted something in the meantime.

If you want to know which values a standard blood test already includes, read what is in a standard blood test. That helps you see what you already have before measuring anything new.

References

• Costello RB, et al. Perspective: The Case for an Evidence-Based Reference Interval for Serum Magnesium. Adv Nutr. 2016. PMID 28140318.
• Duncan A, et al. Quantitative data on the magnitude of the systemic inflammatory response and its effect on micronutrient status. Am J Clin Nutr. 2012. PMID 22158726.
• Lowe NM, et al. Methods of assessment of zinc status in humans: a systematic review. Am J Clin Nutr. 2009. PMID 19420098.
• Rayman MP. Selenium and human health. Lancet. 2012. PMID 22381456.
• Schlueter K, et al. Erroneous potassium results: preanalytical causes, detection and corrective actions. Crit Rev Clin Lab Sci. 2023. PMID 37042478.
• Payne RB, et al. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973. PMID 4758544.
• Voedingscentrum. Minerals and trace elements.
• Gezondheidsraad. Dietary reference values for vitamins and minerals.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.