You need roughly 9 milligrams of zinc a day and around 70 micrograms of selenium. That is less than a grain of salt. Hundreds of enzymes in your body still refuse to work without them.
Trace elements are minerals you need in tiny amounts. Zinc, selenium, copper and iodine are the best known. The word "trace" refers to the quantity, not the importance.
Here is the awkward part: these are precisely the substances a normal blood value reads worst. I will explain why below, because whoever sells you such a test rarely will.
What do zinc, selenium and copper do?
They are mostly building blocks of enzymes. Zinc sits in enzymes involved in your immune defence, your wound healing and your sense of taste. Selenium sits in proteins that protect cells from damage and help convert your thyroid hormone. Copper plays a role in iron transport and in connective tissue.
Selenium is the trace element with the clearest geographical angle. The amount in food depends on how much selenium is in the soil, and that varies strongly by region (Rayman 2012, PMID 22381456). Northern European soils contain relatively little, which makes intake here lower than in, say, the United States.
| Trace element | Role in the body | Main sources |
|---|---|---|
| Zinc | Immune defence, wound healing, taste and smell | Meat, shellfish, nuts, wholegrains, pulses |
| Selenium | Cell protection, thyroid hormone | Brazil nuts, fish, egg, wholegrains |
| Copper | Iron transport, connective tissue, nervous system | Nuts, seeds, cocoa, organ meat |
| Iodine | Raw material for thyroid hormone | Bread with bakery salt, fish, dairy |
Iodine is a separate story in the Netherlands. Because iodine is added to bakery salt as standard, most people get enough. Anyone who eats no bread misses that source. The RIVM tracks iodine intake in the population for exactly this reason.
Why is zinc hard to measure in blood?
Because zinc in your blood falls as soon as inflammation is present, even if your intake is fine. Your body moves zinc to the liver and the tissues where it is needed. The result reads low while there is nothing wrong with your diet. Without an inflammation marker beside it, a zinc result is therefore hard to interpret.
This has been measured properly: during a systemic inflammatory response, plasma concentrations of several micronutrients can fall sharply with no change in intake (Duncan 2012, PMID 22158726). A systematic review of the methods for assessing zinc status reaches the same conclusion: plasma or serum zinc is a blunt measure with real limitations (Lowe 2009, PMID 19420098).
Imagine two people with a zinc of 9 micromoles per litre, so on the low side. One has a CRP of 2 mg/l and eats a one-sided diet. The other has a CRP of 40 mg/l from an infection last week. In the first, something may genuinely be going on. In the second, it is probably the inflammation pushing the number down. Same result, different conclusion.
My position: a zinc measurement without a CRP beside it is half a job. Read them together or not at all.
How do you recognise a trace element shortage?
By very little, frankly. The complaints are vague and overlap with dozens of other causes: reduced resistance, slow wound healing, hair loss, altered taste. A true shortage is uncommon here on a varied diet, and most people who worry about it turn out to have normal values.
You are mainly at risk if you leave out a whole food group or if your absorption is disturbed. Eating fully plant-based lowers zinc absorption, because phytates in grains and pulses bind zinc. Gut conditions can disturb the uptake of several trace elements at once.
Selenium is not free of measurement problems either. There too, serum values give a rough impression and the method chosen matters (Ashton 2009, PMID 19420095).
When do you have trace elements measured?
Measuring is mainly useful when there is a concrete reason: a strongly restricted diet, gut complaints or a condition affecting absorption, or long-standing complaints with no explanation. On a varied diet without symptoms, a stand-alone measurement adds little.
If you do it, measure an inflammation marker alongside. Otherwise you cannot tell whether you are looking at your diet or at your immune system. At Vitalcheck you can have zinc, selenium and copper measured in an extended health checkup, without a referral.
For how these substances relate to the larger minerals, read the pillar on minerals and trace elements. If vitamins are more your concern, read vitamin deficiency and which vitamins to test. Discuss any abnormal result with your GP before you start supplementing.
References
- Rayman MP. Selenium and human health. Lancet. 2012. PMID 22381456.
- Lowe NM, et al. Methods of assessment of zinc status in humans: a systematic review. Am J Clin Nutr. 2009. PMID 19420098.
- Ashton K, et al. Methods of assessment of selenium status in humans: a systematic review. Am J Clin Nutr. 2009. PMID 19420095.
- 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.
- RIVM. Iodine intake in the Netherlands.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
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