Zinc deficiency: symptoms, causes, testing and how it is treated

Zinc is a trace mineral the body keeps no reserve of, so it needs a steady supply from food. The adult body holds only about 2 to 3 grams of zinc in total, mostly in muscle and bone ². When intake falls short or losses rise, the first signs are vague: food tastes flat, cuts heal slowly, colds linger.

Zinc deficiency is characterized by growth retardation, loss of appetite, and impaired immune function.NIH Office of Dietary Supplements, Zinc fact sheet for health professionals ¹

Symptoms of zinc deficiency

Zinc deficiency symptoms follow the jobs zinc does. Zinc is needed to copy DNA, make new skin and gut lining, run immune cells and sense taste, so the tissues that renew fastest show the shortage first. Mild zinc deficiency is easy to miss because its symptoms overlap with low iron, low B12 and an underactive thyroid.

Doctors call the severe rash pattern acrodermatitis: a rash at the ends of the body, around the mouth, hands, feet and groin. A rare inherited form, acrodermatitis enteropathica, blocks zinc absorption from the gut from birth. It shows up in babies with rash, hair loss and diarrhea and needs lifelong zinc under medical care ⁴.

Can low zinc cause hair loss?

Severe zinc deficiency causes hair loss, and the hair grows back once zinc is restored ⁴. Everyday hair shedding is a weaker case. A Korean study of people with hair loss (alopecia areata, telogen effluvium and male and female pattern hair loss) found lower average serum zinc than in healthy controls ⁶, but a lower average across a group does not show that zinc tablets regrow hair in someone whose zinc is normal. Iron stores and thyroid function are the two other common, checkable causes of diffuse shedding; see hair loss and iron deficiency.

What causes low zinc

Low zinc comes from one of four places: too little going in, too little being absorbed, too much being lost, or more being needed.

Who is most at risk

• Vegetarians and vegans, who may need up to 50% more zinc than the standard recommendation because of phytate in grains and beans ⁵
• Pregnant and breastfeeding women
• People with gut disease or after weight-loss surgery ¹
• People with alcohol use disorder ¹
• People with sickle cell disease ¹
• Infants older than about 6 months who are exclusively breastfed and not yet eating zinc-rich foods ¹
• Older adults with a small appetite

How zinc deficiency is tested, and why a normal result can miss it

Doctors test zinc with a serum or plasma zinc level, the zinc blood test. It is the best single test available and it is still a blunt one. Only about 0.1% of the body's zinc circulates in plasma, and the body holds that small pool steady, so plasma zinc tends to fall late, after tissues are already short ². A normal serum zinc result therefore does not rule out a mild zinc deficiency.

A low result can also be a false alarm. Serum zinc falls during any infection or inflammation, because the liver pulls zinc out of the blood as part of the immune response; it reads lower when albumin (the blood protein that carries most zinc) is low, after a meal, and in the afternoon ². Serum zinc reads falsely high when red cells burst in the tube (hemolysis) or when the sample goes into a standard tube rather than a special metal-free one ². A low serum zinc during a bad cold may only mean the cold.

These IZiNCG cut-offs are for groups and sample types, not a lab's printed range, which is one reason the numbers on your report may differ; see why reference ranges differ. Afternoon samples have their own, lower cut-offs, so the time of the draw belongs on the request ². Red blood cell zinc and hair zinc are sold as longer-term measures, but neither is an established test for diagnosing zinc deficiency in an individual ².

For why a raised CRP changes how other results read, see inflammation markers explained; for what a low albumin means on its own, see low albumin. Getting the sample right matters more for zinc than for most tests, so the blood test preparation guide is worth a look before a repeat draw.

Got a low zinc result? How to read it

1. 1Check when the sample was takenA low serum zinc from an afternoon or after-breakfast draw is weaker evidence than the same number from a fasting morning sample.
2. 2Check CRP and albumin from the same drawA raised CRP or a low albumin at the time can explain a low serum zinc without any true zinc deficiency.
3. 3Look at how far below the cut-off it isA serum zinc a few points under the cut-off is borderline; a result well below it, such as under 50 µg/dL, is harder to explain away. A result well below the cut-off, or a low result with a spreading rash, diarrhea or poor growth in a child, should go to a doctor rather than be treated with shop-bought zinc.
4. 4Match it to symptoms and riskA low serum zinc in someone with Crohn's disease, a vegan diet or past weight-loss surgery, and with slow healing or taste changes, is more likely to be real.
5. 5Repeat when wellFor a borderline result with no clear cause, ask your doctor to repeat zinc together with CRP and albumin as a fasting morning sample once any illness has passed. If treatment starts, ask when the follow-up test should be.

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For a general method that works on any line of a report, see how to read any lab result.

How to fix zinc deficiency: food, supplements and time

Treatment of zinc deficiency has two parts: fixing the cause where possible (a gut condition, a medicine, alcohol) and restoring zinc through food and, when a doctor judges it needed, a supplement course for a set period. The dose and length of a course depend on how low the zinc is and why, so a clinician sets them. Treatment doses can sit above the 40 mg upper limit ⁵, which is why a course needs a plan, a stop date and a retest.

For children with acute diarrhea, the WHO and UNICEF recommend that health workers give zinc alongside oral rehydration: 20 mg a day for 10 to 14 days, or 10 mg a day for infants under 6 months ¹. A child with diarrhea and signs of dehydration needs to be seen, not treated at home with zinc alone.

Foods high in zinc

The foods highest in zinc are shellfish and red meat, with seeds and beans as smaller plant sources.

Food values are from the NIH Office of Dietary Supplements, drawing on USDA data ¹. Zinc from meat and seafood is absorbed better than zinc from grains and beans, because phytate in plant foods binds it ¹. Soaking, sprouting and leavening (as in yeast bread) break down phytate and free up more zinc, which matters most on a vegetarian or vegan diet.

Zinc supplements list the elemental zinc on the label, and the form changes how much of the tablet is zinc: zinc sulfate is about 23% elemental zinc and zinc gluconate about 14% ¹. Our zinc page covers the forms and the evidence in full.

The supplement studied for low zinc

Strongest evidence (for deficiency)ZincRestores zinc in people with a confirmed deficiency; benefits when zinc is already normal are much less clear.In our shop

Zinc side effects: too much zinc lowers copper

The adult upper limit for zinc is 40 mg a day from food and supplements combined ⁵. Taking around 50 mg or more of supplemental zinc a day for weeks to months can cause copper deficiency ¹⁵: zinc makes gut cells produce metallothionein, a protein that grabs copper and holds it so it is shed with the gut lining instead of absorbed ¹. Copper deficiency can cause anemia, low neutrophils (a type of white blood cell) and nerve damage with numbness and tingling and an unsteady walk ¹. Large single doses of zinc cause nausea, vomiting and stomach cramps, and zinc nasal sprays and gels have been linked to lasting loss of smell ¹.

For copper on its own, see copper.

Zinc deficiency vs look-alikes

These conditions often travel together: the gut diseases and diets that lower zinc also lower iron and B12, so a doctor investigating suspected zinc deficiency will often check all three.

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