Zinc is a mineral needed for hundreds of enzymes, immunity, wound healing, taste, smell and protein synthesis. It is also a cofactor of the enzyme alkaline phosphatase.
As with magnesium, zinc has a catch: only a small part of its stores is in the blood, so a serum test reflects a deficiency in the tissues poorly.
Reference ranges
The reference range depends on the lab; approximate values:
| Normal (serum) | ≈ 11 – 18 µmol/L |
| Deficiency | immunity, skin, taste, healing |
| Hidden deficiency | symptoms with a "normal" test |
| Excess | rare, usually from supplements |
What an elevated level means
An excess of zinc is rare and almost always due to excessive supplement use. A prolonged excess of zinc impairs the absorption of copper, which over time can lead to copper deficiency (anemia, neurological symptoms).
So high doses of zinc should not be taken without a reason.
What a low level means
Zinc deficiency is a more common problem, especially with a monotonous diet, bowel disease and in older people.
Signs: frequent infections and slow wound healing, hair loss, dry skin and rashes, a reduced sense of taste and smell, and in children, stunted growth. Deficiency develops with a vegetarian diet (poorer absorption from plants), diarrhea and alcohol misuse.
How the test is done
Zinc is measured in serum from a vein, ideally in the morning on an empty stomach. Remember the method's limitation: the test can be normal despite a tissue deficiency, and inflammation lowers the result.
So zinc deficiency is often assessed from the whole picture: diet, symptoms and risk factors, not just the figure in the test.
What affects the value
- Inflammation — lowers serum zinc (redistribution).
- A vegetarian diet — poorer absorption from plants.
- Bowel disease and diarrhea — lower it.
- Alcohol — increases zinc losses.
- Excess zinc supplements — impair copper absorption.
- Food intake and time of day — affect the result.
Frequently asked questions
How can you tell you are short of zinc?
Frequent infections, slow wound healing, hair loss, skin problems and a reduced sense of taste and smell help raise the suspicion of deficiency. A blood test supports the diagnosis but can be normal despite a tissue deficiency, so diet and symptoms matter.
Why is the zinc test not always accurate?
Only a small part of the body's zinc is in the blood, and inflammation temporarily lowers its level by redistributing it into the tissues. So a normal serum zinc does not rule out a deficiency, and the result is interpreted together with the clinical picture.
Can you overdo zinc?
Yes. High doses of zinc in supplements, taken over a long time, impair copper absorption and can lead to copper deficiency with anemia and neurological symptoms. So zinc is taken as indicated and in sensible doses.
Related terms
Sources
- MedlinePlus (NIH) — Zinc in Diet
- NIH Office of Dietary Supplements — Zinc
- Zinc deficiency (review). NCBI/StatPearls