What does zinc do?

What are the health benefits of zinc?

Zinc is vital for a healthy immune system, correctly synthesizing DNA, promoting healthy growth during childhood, and healing wounds.

The following are some of the health benefits of zinc:

1) Zinc and regulating immune function

According to the European Journal of Immunology, the human body needs zinc to activate T lymphocytes (T cells).

T cells help the body in two ways:

  1. controlling and regulating immune responses
  2. attacking infected or cancerous cells

Zinc deficiency can severely impair immune system function.

According to a study published in the American Journal of Clinical Nutrition, “zinc-deficient persons experience increased susceptibility to a variety of pathogens.”

2) Zinc for treating diarrhea

According to the World Health Organization, diarrhea kills an astonishing 1.6 million children under 5 every year. Zinc pills may help reduce diarrhea.

A PLoS Medicine study, which “followed a nationwide public health campaign to increase zinc use for childhood diarrhea in Bangladesh,” confirmed that a 10-day course of zinc tablets is effective at treating diarrhea and also helps prevent future bouts of the condition.

3) Zinc effects on learning and memory

Research conducted at the University of Toronto and published in the journal Neuron suggested that zinc has a crucial role in regulating how neurons communicate with one another, affecting how memories are formed and how we learn.

4) Zinc to treat the common cold

Zinc lozenges were found to shorten the duration of common cold episodes by up to 40 percent in a study published in the Open Respiratory Medicine Journal.

In addition, a Cochrane review concluded that taking “zinc (lozenges or syrup) is beneficial in reducing the duration and severity of the common cold in healthy people, when taken within 24 hours of onset of symptoms.”

5) Zinc’s role in wound healing

Zinc plays a role in maintaining skin integrity and structure. Patients experiencing chronic wounds or ulcers often have deficient zinc metabolism and lower serum zinc levels. Zinc is often used in skin creams for treating diaper rash or other skin irritations.

A Swedish study that analysed zinc in wound healing concluded, “topical zinc may stimulate leg ulcer healing by enhancing re-epithelialization, decreasing inflammation and bacterial growth. When zinc is applied on wounds, it not only corrects a local zinc deficit but also acts pharmacologically.”

However, research has not consistently shown that use of zinc sulfate in patients with chronic wounds or ulcers is effective at improving healing rate.

6) Zinc and decreased risk of age-related chronic disease

A study from researchers at Oregon State University have found that improving zinc status through diet and supplementation may reduce the risk of inflammatory diseases. It has been known for decades that zinc has a significant role in immune function. Deficiency has been linked to increased inflammation in chronic disease and triggering new inflammatory processes.

8) Zinc for preventing age-related macular degeneration (AMD)

Zinc prevents cellular damage in the retina, which helps in delaying the progression of AMD and vision loss, according to a study published in the Archives of Ophthalmology.

9) Zinc and fertility

Several studies and trials have linked poor zinc status with low sperm quality. For example, one study in the Netherlands found that subjects had a higher sperm count after zinc sulfate and folic acid supplementation. In another study, researchers concluded that poor zinc intake may be a risk factor for low quality of sperm and male infertility.

10) Other possible zinc benefits

Zinc may also be effective for the treatment of:

  • acne – one study, published in JAMA, showed promising results of zinc sulfate for the treatment of acne
  • attention deficit hyperactivity disorder (ADHD)
  • osteoporosis
  • preventing and treating pneumonia

Here’s What Happens When You Take Too Much Zinc

Zinc is an essential nutrient for protecting our immune systems from viruses and bacteria, helping wounds to heal, and making protein and DNA in the body. It’s even important for providing us with a proper sense of smell and taste.

Zinc can be obtained from oysters, meat, poultry, and some plant-based foods. It’s also a popular supplement, especially during flu season. While it’s crucial to make sure we get enough of this nutrient—11mg per day for men and 8mg for women—consuming too much has serious consequences.

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Flu-Like Symptoms

Too much zinc can actually make you feel like you have the flu, with symptoms like nausea, fever, vomiting, and coughing. If you regularly consume foods with high levels of zinc, such as meat and fortified cereals, there is no need to up your zinc intake during flu season, as it can produce this reverse effect.

Diarrhea and Abdominal Pain

This is a common symptom for those who have consumed too much zinc, and one study showed it was linked to 40 percent of participants who took a zinc supplement to fight a cold. Diarrhea is not only uncomfortable, but it can be dangerous when you’re sick, as it dehydrates you even more.

Looking for more tips on fighting the flu?

  • It’s Flu Season: Here’s What Happens When You Take Too Many Vitamins
  • Skip the Drug Store, Drink These Cold and Flu Fighters Instead
  • 6 Immunity-Boosting Foods to Keep on Hand All Winter Long

Copper Deficiency

The presence of too much zinc in the body prevents it from properly absorbing copper, an essential mineral for creating red blood cells. Copper deficiencies can lead to anemia, which inhibits energy levels, concentration, and breathing ability. Too little copper in the body can also cause numbness or pain in your limbs.

Zinc and Antibiotics

Taking an oral zinc supplement can inhibit certain antibiotics from fighting off illness. Tetracycline and quinolone, popular antibiotic options, need to be taken several hours after a zinc supplement to minimize the effect. However, you might be better off ditching the supplement for a few weeks to make sure the antibiotic can do its job.

The bottom line: Consuming a variety of whole, healthful foods is always the best way to get enough of the nutrients you need. Supplements should be just that—a supplement to a nutritious diet, and should never be considered as a replacement for healthy food.

If you do want to take a zinc supplement, it’s important to note they are often sold in large doses, and don’t need to be taken every day. More importantly, make sure you’re eating lean meats, whole grains, nuts, and beans to help your body produce the zinc it needs to keep you strong and healthy this flu season.

Zinc is great for us in many ways, and we can get a dose of it by eating dairy, oysters, red meat, or even beans and nuts . . . but when adding supplements to the mix, it’s important to know when we’re going a bit too far.

“Taking too much zinc may cause symptoms such as nausea, vomiting, stomach cramps, loss of appetite, diarrhea, and headaches. Long-term ingestion of zinc can lower your good cholesterol HDL, decrease immunity, and lower your copper levels,” said South Florida cardiologist Adam Splaver, MD, NanoHealth Associates.

Many people associate zinc with a healthy immune system, but it also works to support your nervous system. “I recommend it for people with drained brains because it acts as a cofactor — helping your body to manufacture the stress-relieving neurotransmitters GABA and serotonin from the amino acids in your diet,” said renowned psychotherapist and author of Heal Your Drained Brain, Dr. Mike Dow.

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Too much of a good thing becomes a bad thing, and it does happen. “Zinc toxicity is relatively rare and usually manifests first with nausea and or vomiting and taste changes (especially when using zinc lozenges) and then — to a lesser extent — fatigue and lethargy,” said Joel Totoro, RD, who works with Thorne Research.

The negative implications of higher-than-recommended zinc intakes are the result of zinc’s impact on copper levels. “Both zinc and copper activate a cell protein in the intestines that binds to both metal ions but has a much higher preference for copper,” Totoro said.

Excess zinc causes the body to remove even more copper, which can result in a copper deficiency over time. “Osteoporosis and impaired growth have been linked to a copper deficiency, most commonly in children,” Totoro said.

Zinc recommendations are split into two categories: “Low dose for maintenance and to meet daily needs and high-dose protocols to correct a deficiency. Athletes and those with high sweat rates and vegan/vegetarians are at a higher risk for deficiency,” said Totoro, who explained that zinc is one of the minerals that is lost in sweat, so the more you sweat, the more zinc you need. Totoro made the following dosage recommendations:

Low-Dose Recommendations: 8 mg/day for women, 10-12 mg/day for pregnant women, 14-15 mg/day for men

High-Dose Recommendations: 25-40 mg/day

The Tolerable Upper Limit (TUL): 40 mg/day

Short-term doses (two to three months) of 100 mg/day have been considered safe but should only be used under medical supervision to correct a deficiency, and attention should be paid to copper status.

Supplemental zinc comes in many forms, with varying zinc concentrations. Zinc picolinate is considered the most bioavailable, followed by zinc gluconate and zinc citrate.

If you are taking a multivitamin, check the ingredients. “You probably have zinc in the vitamin. And this is one vitamin where too much is not a good thing,” Dr. Splaver said.

Image Source: Unsplash / Jonathan Perez

Zinc in diet

REFERENCE INTAKES

Dosages for zinc, as well as other nutrients, are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board at the Institute of Medicine. DRI is a term for a set of reference intakes that are used to plan and assess the nutrient intakes of healthy people. These values, which vary by age and gender, include:

  • Recommended Dietary Allowance (RDA) — The average daily level of intake that is enough to meet the nutrient needs of nearly all (97% to 98%) healthy people. An RDA is an intake level based on scientific research evidence.
  • Adequate Intake (AI) — This level is established when there is not enough scientific research evidence to develop an RDA. It is set at a level that is thought to ensure enough nutrition.

Dietary Reference Intakes for zinc:

Infants (AI)

  • 0 to 6 months: 2 mg/day

Children and infants (RDA)

  • 7 to 12 months: 3 mg/day
  • 1 to 3 years: 3 mg/day
  • 4 to 8 years: 5 mg/day
  • 9 to 13 years: 8 mg/day

Adolescents and Adults (RDA)

The best way to get the daily requirement of essential vitamins and minerals is to eat a balanced diet that contains a variety of foods.

Why you should start taking zinc – today

Zinc is an immunity-boosting powerhouse. Here’s why you need to make sure your levels are topped up.

It’s not just a high-scoring word in Scrabble – zinc is also essential for our health and wellbeing.

We need zinc to help the body create new cells and process food. It also helps us to resist infection. Find out why everybody’s body could benefit from a healthy zinc intake.

What is zinc?

Zinc is the second most common mineral found in our bodies, after iron. It’s in every cell, from our organs to our bones, tissues and fluids.1

Foods high in zinc include:
• shellfish
• cheese
• meat
• legumes including chickpeas
• nuts and seeds
• wholemeal bread
• fortified vegan foods

Handpicked content: Is too much iron bad for you?

Why do we need zinc?

We don’t need a lot of zinc to help our bodies work efficiently – 7mg a day for women, 9.5mg for men2 – but that small amount has a whole host of benefits.

Zinc cuts the length of a cold

A meta-analysis of research published in Open Forum Infectious Diseases in 2017 found that zinc acetate lozenges can speed up recovery from colds. On the fifth day of the cold, 70% of sufferers who took zinc had recovered compared with 27% of those who took a placebo.3

In 2015, an Australian trial also found that high-dose zinc lozenges (80mg a day) cut the duration of nasal discharge by 34%, nasal congestion by 37%, scratchy throat by 33%, and cough by 46%.4

Zinc fights inflammation

Inflammation is a natural response by the body to fighting infection, but when it persists is can lead to chronic conditions such as heart disease, rheumatoid arthritis, depression and Alzheimer’s Disease.5

The good news is zinc has anti-inflammatory activity. A study by Jagiellonian University Medical College in Poland in 2017 discovered that zinc ‘exhibits antioxidant and anti-inflammatory activity’ which can potentially deter ill-health.6

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Zinc boosts immunity

A 2017 US study carried out over six weeks found that taking just an 4mg extra of zinc a day made a major difference to the health of cells, which in turn makes your body better able to fight infections and diseases.7

The team concluded that zinc reduces ‘oxidative stress and damage to DNA’ that helps protect against chronic diseases.

Zinc is good for fertility

Zinc has long been associated with a positive impact on male fertility. One study of 200 men published in the journal Fertility and Sterility in 2002 confirmed that normal sperm count increased after taking combined zinc sulfate and folic acid, in both fertile and sub-fertile men.8

How zinc interacts with copper

It’s not just a zinc deficiency that can cause a problem. If you consume too much zinc, this can reduce the amount of copper the body can absorb, so don’t take more than 25mg a day unless advised by your doctor.

Advice is for information only and should not replace medical care. Please consult a doctor or healthcare professional before trying any remedies.

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Sources

The role of zinc in the body

Zinc is an essential trace element and has a number of roles and functions in the human body.

  • It is an essential component/cofactor for more than 300 enzymes involved in the synthesis and metabolism of carbohydrates, lipids, proteins, nucleic acids and other micro-nutrients.
  • It stabilises cellular components and membranes and so is important for cell and organ structure and integrity.
  • It is essential for cell division and is needed for normal growth and development during pregnancy, childhood and adolescence.
  • It is involved in DNA synthesis and the process of genetic expression.
  • It is important for immune function (both cellular and humoral immunity).
  • It is involved in wound healing and tissue repair.
  • It is needed for the senses of taste and smell.

How much zinc?

  • An average-sized adult male has 1.4 to 2.3  g of zinc.
  • Approximately 60% of the total body zinc content is found in skeletal muscle and 30% in bone mass.
  • The choroid of the eye and prostatic fluid have high concentrations of zinc..
  • Zinc is absorbed predominantly in the duodenum and proximal jejunum, and excreted mainly in the faeces.
  • There are no body stores of zinc and so daily intake of zinc is needed to maintain adequate body levels.
  • The recommended daily zinc intake (reference nutrient intake) for an adult man in the UK is 9.5 mg.
  • The recommended daily zinc intake for an adult woman in the UK is 7 mg.
  • Mean consumption of zinc for an adult is about 10-15  mg daily.
  • The Department of Health in the UK advises that intake of zinc should not exceed 25 mg per day.

Dietary sources of zinc

Zinc-rich foods:

  • Red meat and poultry (these are the main sources of zinc for many).
  • Oysters, crab, lobster and other shellfish (oysters contain more zinc per serving than any other food).
  • Pulses, nuts and legumes.
  • Wholegrain cereals.
  • Fortified breakfast cereals.
  • Dairy products such as cheese.

Note that phytates in wholegrain bread, cereals, legumes and some other foods inhibit zinc absorption and so affect the bioavailability of zinc from plant foods.

Zinc deficiency

Risk factors

  • Inadequate diet.
  • Gastrointestinal diseases including ulcerative colitis, Crohn’s disease, short bowel syndrome and chronic diarrhoea.
  • Chronic liver disease.
  • Chronic kidney disease.
  • Alcohol dependency (decreases zinc absorption and increases urinary zinc excretion).
  • Sickle cell disease.
  • Diabetes.
  • Pregnancy and breastfeeding.
  • Vegetarian diet.
  • People taking large amounts of iron supplementation (iron can interfere with zinc absorption).

Presentation

This depends on the severity of zinc deficiency.

  • Anorexia, lethargy, diarrhoea.
  • Growth restriction (delayed bone maturation).
  • Impaired immune function and susceptibility to infection.

Severe cases can lead to:

  • Delayed sexual maturation, impotence, hypogonadism and hypospermia.
  • Alopecia, dermatitis, paronychia.
  • Intellectual disability, impaired nerve conduction and nerve damage.
  • Weight loss.
  • Macular degeneration.
  • Impaired taste and smell.
  • Impaired wound healing.
  • Impaired iron absorption.

Investigations

  • Diagnosis may be difficult to confirm because plasma and serum zinc levels do not necessarily reflect cellular zinc status.
  • Clinical signs and effects of zinc deficiency may be present with normal laboratory values.
  • Clinicians need to have a high index of suspicion, particularly if risk factors are present.

Management

  • This is based on both treatment of any underlying cause and zinc supplementation.
  • Dietary advice should also be given.

Acrodermatitis enteropathica

  • Acrodermatitis enteropathica can either be inherited or acquired.
  • The acquired form can arise in people with a zinc-deficient diet.
  • The inherited form is a rare autosomal recessive disorder leading to failure to generate a transport protein that enables zinc to be absorbed in the intestine:
    • Symptoms usually begin after an infant is weaned from breast milk.
    • It presents with a characteristic pustular rash over the mucocutaneous junctions, particularly around the mouth and around the anus and genital areas.
    • Hair loss, nail dystrophy, failure to thrive and severe diarrhoea are also features.
    • Atrophy of the brain cortex can lead to irritability and emotional disturbances.
    • Secondary bacterial and fungal infections may also occur.
    • Treatment is with zinc supplements.
    • If treated early, most of the symptoms are reversible and usually leave no sequelae.
    • Therapy is lifelong and total compliance is essential.

Zinc excess and zinc toxicity

  • Zinc may accumulate in acute kidney injury.
  • Those with haemochromatosis may absorb larger amounts of zinc.
  • Various pesticides contain zinc salts.
  • Compounds used to make paints, rubber and dyes may also contain zinc.
  • Zinc toxicity may be acute or chronic.
  • Acute toxicity (ingesting more than 200 mg/day of zinc) can cause:
    • Abdominal pain, nausea, vomiting and diarrhoea.
    • Other reported effects – these include gastric irritation, headache, irritability, lethargy, anaemia and dizziness.
  • Prolonged intake of zinc ranging from 50-150 mg/day can lead to:
    • Disturbance of copper metabolism, causing low copper status, reduced iron function, red blood cell microcytosis, neutropenia and reduced immune function.
    • It can also lead to reduced levels of high-density lipoproteins and so it has been suggested that excessive zinc intake may be atherogenic.
    • Excess zinc can also affect cardiac function and can impair the pancreatic enzymes amylase and lipase.
  • Blood zinc levels can be measured to assess toxicity.
  • Treatment is symptomatic.

Metal fume fever

  • Inhalation of fumes containing zinc oxide may cause metal fume fever.
  • Metal fume fever can also follow inhalation of fumes of copper, magnesium, aluminium, antimony, iron, manganese and nickel during welding, galvanising or smelting.
  • Symptoms may occur within 3-10 hours of exposure and usually resolve within 1-2 days.
  • Symptoms include cough, dyspnoea, sore throat, chest pain, headache, fever, rigors, myalgia, arthralgia and gastroenteritis.
  • Management of metal fume fever includes removing the patient from exposure, oxygen as required, and symptomatic treatment for pain and fever.

Zinc supplements

  • A number of different forms of zinc are available as supplements, including zinc sulfate, zinc gluconate and zinc acetate.
  • Zinc supplements must be used with caution in view of the dangers of zinc excess and zinc toxicity.

Indications for zinc supplementation

These include:

  • Proven zinc deficiency and zinc-losing conditions.
  • Zinc acetate is used to treat Wilson’s disease.
  • Total parenteral nutrition regimens usually include trace amounts of zinc. If necessary, further zinc can be added to intravenous feeding regimens.

Supplementation during acute diarrhoea in children

  • In developing countries, acute diarrhoea in children is associated with high mortality rates.
  • The World Health Organization (WHO) recommends zinc supplementation for 10-14 days (20 mg daily; 10 mg daily for children aged under 6 months) in children with acute diarrhoea in such countries because studies have shown that this shortens the course of the diarrhoea.

Supplementation as treatment for the common cold

  • Lozenges containing at least 75 mg have been the most widely studied but their use needs to be balanced against side-effects of nausea and bad taste.
  • No sufficient evidence was found to support prophylactic zinc supplementation for the common cold.

Supplementation for age-related macular degeneration (AMD)

  • The Age-Related Eye Disease Study (AREDS) was a large, randomised, placebo-controlled trial looking at the effect of high-dose antioxidant (beta-carotene, vitamin C and vitamin E) and zinc supplements on the development of advanced AMD in people who already had different degrees of AMD.
  • When both antioxidants and zinc were taken, the risk of developing advanced AMD was significantly reduced and visual acuity loss was reduced as well.
  • Supplementation with zinc alone reduced the risk of advanced AMD in high-risk individuals but not in the total study population.
  • Zinc supplementation alone did not have a significant effect on visual acuity loss.
  • A Cochrane review also supported the use of antioxidant and zinc supplementation in those with AMD.

Cautions

  • Zinc may accumulate in acute kidney injury.
  • Those with haemochromatosis may absorb larger amounts of zinc.
  • Excess zinc supplementation can interfere with iron and copper absorption.
  • It can also reduce magnesium and calcium absorption.

Interactions

  • Quinolone and tetracycline antibiotics may interact with zinc supplements, leading to reduced absorption of the supplement and the antibiotic.
  • Zinc supplementation can reduce the absorption of penicillamine.
  • Prolonged use of thiazide diuretics increases urinary excretion of zinc and so can reduce tissue levels.

Side-effects

  • Irritability, headache, lethargy.
  • Unpleasant taste in the mouth.
  • There have been reports of anosmia with intranasal zinc preparations.
  • Gastrointestinal effects, including abdominal pain, dyspepsia, nausea, vomiting, diarrhoea, gastric irritation, and gastritis. This is more likely when supplements are taken with little or no food.
  • Prolonged use of high doses of zinc can result in deficiency of copper.

Background

Zinc is a component of various enzymes that help maintain structural integrity of proteins and regulate gene expression. Zinc metalloenzymes include ribonucleic acid polymerases, alcohol dehydrogenase, carbonic anhydrase and alkaline phosphatase. The biological function of zinc can be catalytic, structural or regulatory. More than 85% of total body zinc is found in skeletal muscle and bone (King & Keen 1999).

Zinc is widely distributed in foods. Meats, fish and poultry are the major contributors to the diet but cereals and dairy foods also contribute substantial amounts. The presence of zinc in foods as a complex rather than as free ions affects its bioavailability. The environment within the gastrointestinal tract, which can be affected by other dietary constituents, markedly influences the solubility and absorptive efficiency of zinc (Cousins 1989, Lonnerdal 1989). The amount of protein in the diet is a factor contributing to the efficiency of zinc absorption as zinc binds to protein. Small changes in protein digestion may produce significant changes in zinc absorption (Sandstrom & Lonnerdal 1989). The markedly greater bioavailability of zinc from breast milk than from cow’s milk is an example of how the lower protein digestibility of cow’s milk influences zinc absorption (Roth & Kirchgessner 1985). In general, zinc absorption from a diet high in animal protein will be greater than from a diet rich in plant derived proteins (King & Keen 1999). The requirement for dietary zinc may be as much as 50% greater for vegetarians, particularly strict vegetarians whose major staples are grains and legumes and whose dietary phytate:zinc ratio exceeds 15:1.

Dietary intake of iron at levels found in some supplements can decrease zinc absorption, which is of particular concern in the management of pregnancy and lactation. High intakes of calcium have been shown to have a negative effect on zinc absorption in animal experiments, but human data are equivocal with calcium phosphate decreasing zinc absorption (Wood & Zheng 1997) and calcium as citrate-malate complex having no effect (McKenna et al 1997). Current data suggest that consumption of calcium-rich diets does not have a major effect on zinc absorption at an adequate intake level. There is also some evidence of potential interrelationship of zinc with copper and folate, but studies are limited. Regulation of zinc metabolism is achieved through a balance of absorption and secretion of reserves and involves adaptive mechanisms related to dietary zinc intake.

Zinc depletion in humans results in reduced endogenous zinc loss and increased efficiency of intestinal zinc absorption. While plasma zinc is only 1% of the body’s total, its concentration is tightly regulated and is generally not affected by mild deficiency. Situations of stress, acute trauma and infection can lead to lower plasma zinc. Mild deficiency can result in impaired growth velocity, suboptimal pregnancy outcomes and impaired immune responses. Severe deficiency can result not only in growth impairment but also alopecia, diarrhoea, delayed sexual development and impotency, eye and skin lesions and impaired appetite.

Assessment of requirements is based on estimates of the minimal amount of absorbed zinc necessary to match total daily excretion of endogenous zinc (FNB:IOM 2001). Estimates are made using a factorial approach that involves calculation of both intestinal and non-intestinal losses (via the kidney, skin, semen and menstruation). Although urinary zinc losses decrease markedly with severe deficiency (Baer & King 1984), across a dietary intake range of 4-25 mg/day, urinary zinc (and non-intestinal losses in general) appears to be largely independent of dietary intake. Intestinal losses, however, correlate strongly to absorbed zinc.

To determine the dietary zinc requirement for a given age/gender group, it is necessary to define the relationship between absorption and intestinal losses and adjust by a constant for the non-intestinal losses in order to calculate the minimum quantity of absorbed zinc necessary to offset total endogenous losses. The factorial calculations used are based on metabolic/tracer studies in which participants are fed diets from which the bioavailability of zinc is likely to be representative of typical diets in Australia and New Zealand.

1 mmol zinc = 65.4 mg zinc

Recommendations by life stage and gender

Infants

Age AI
0-6months 2.0 mg/day

Rationale: The AI for 0-6 months was calculated by multiplying together the average intake of breast milk (0.78 L/day) and the average concentration of zinc in breast milk in the early months postpartum, and rounding. Concentrations of zinc in breast milk decline from approximately 4 mg/L at 2 weeks to 3 mg/L at 1 month, 2 mg/L at 2 months, 1.5 mg/L at 3 months and 1.2 mg/L at 6 months postpartum (Krebs et al 1995). The AI was set to match the zinc intake of infants in the early months (2.5 mg/L x 0.78 L/day). This estimate is also consistent with factorial estimates of requirements in infants aged 0-6 months fed breast milk (Krebs et al 1996, Krebs & Hambridge 1986). Although the absorption of zinc is higher from breast milk than from infant formula based on cow’s milk or soy, these formulas generally have a much higher content of zinc than breast milk which compensates for the lower absorption efficiency (Lonnerdal et al 1988, Sandstrom et al 1983).

Age EAR RDI
7-12 months 2.5 mg/day 3 mg/day

Rationale: The EAR for 7-12 months was set by estimating the absorbable zinc required to replace endogenous zinc losses, extrapolating on a body weight basis from adult data and including considerations of growth needs, assuming an absorption of 30% (Davidsson et al 1996, Fairweather-Tait et al 1995) and making an allowance for growth. The RDI was set using a CV of 10% for the EAR and rounding, as information was not available on the SD of the requirement. Absorption is higher from animal foods than plants sources, so vegetarian infants, particularly strict vegetarians, will need higher intakes.

Children & adolescents

Rationale: The absorbed zinc requirement was estimated by summing the estimated non-intestinal (urinary, integument, semen for men ) and intestinal zinc losses to derive total endogenous losses. Endogenous losses for children were calculated using reference weights with an additional requirement for growth The EAR was then estimated assuming an absorption of 24% for boys and 31% for girls (International Zinc Nutrition Consultative Group 2004), and rounding. The RDI was set on the unrounded EAR using a CV of 10% for the EAR and rounding, as information was not available on the SD of the requirement. Absorption is higher from animal foods than plants sources, so vegetarians, particularly strict vegetarians, will need intakes about 50% higher than those set.

Adults

Rationale: The absorbed zinc requirement was estimated by summing the estimated non-intestinal (urinary, integument, semen for men ) and intestinal zinc losses to derive total endogenous losses. The EAR was then estimated assuming an absorption of 24% for men and 31% for women (IZiNCG 2004), and rounding. The RDI was set on the unrounded EAR using a CV of 10% for the EAR and rounding up, as information was not available on the SD of the requirement. Absorption is higher from animal foods than plants sources, so vegetarians, particularly strict vegetarians, will need intakes about 50% higher than those set.

Pregnancy

Age EAR RDI
14-18 yr 8.5 mg/day 10 mg/day
19-30 yr 9.0 mg/day 11 mg/day
31-50 yr 9.0 mg/day 11 mg/day

Rationale: The EAR was established by estimating the needs for the additional maternal and foetal tissues and adding this to the equivalent EAR for non-pregnant females. The figure used was based on late pregnancy estimates of zinc accumulation (the period of greatest need) to give a single recommendation throughout pregnancy. Zinc accumulation at this time averages 0.73 mg/day (Swanson & King 1987). Absorption in pregnancy is thought to be similar to that of non-pregnant women, so an absorption rate of 31% was used to estimate the additional requirement of 2.35 mg/day. Absorption is higher from animal foods than plant sources, so vegetarians, particularly strict vegetarians, will need intakes about 50% higher than those set.

Note: For women taking high levels of iron supplements during pregnancy and lactation, the current EAR and thus RDI may not be adequate. There is some evidence that high levels of iron supplements prescribed to pregnant and lactating women may decrease zinc absorption. (Fung et al 1997, Hambidge et al 1983, O’Brien et al 2000)

Lactation

Age EAR RDI
14-18 yr 9 mg/day 11 mg/day
19-30 yr 10 mg/day 12 mg/day
31-50 yr 10 mg/day 12 mg/day

Rationale: The lactation recommendation was based on consideration of the additional needs for milk production together with estimates of zinc released for use because of decreasing maternal blood volume (King & Turland 1989). This averages about 30 mg zinc that can be re-used. The average increased requirement for absorbed zinc is 1.35 mg/day. Absorption is about 42% in lactation (Fung et al 1997), giving an additional dietary zinc requirement of 3.2 mg/day. Absorption is higher from animal foods than plants sources, so vegetarians, particularly strict vegetarians, will need intakes about 50% higher than those set.

Upper Level of Intake

Rationale: There is no evidence of adverse effects from naturally occurring zinc in food. The UL applies to total zinc intake from food, water and supplements (including fortified food). Adverse events associated with chronic intake of supplemental zinc include suppression of immune response, decrease in high density lipoprotein (HDL) cholesterol and reduced copper status. The adverse effect of excess zinc on copper metabolism has been identified as the critical effect on which to base the UL. This is based on the consistency of findings (Fischer et al 1984, Samman & Roberts 1988, Yadrick et al 1989), the sensitivity of the marker used (erythrocyte copper-zinc superoxide dismutase) and the quality and completeness of the database for this endpoint. A LOAEL of 60 mg/day is based on the studies of Yadrick et al (1989) and is supported by other studies (Fischer et al 1984). A UF of 1.5 is applied to account for inter-individual variability in sensitivity and for extrapolation from LOAEL to NOAEL. As reduced copper status is rare in humans, a higher UF was unjustified. The adult UL was therefore set at 40 mg/day. There was inadequate data to justify a different UL for pregnancy and lactation and so the level is set at that for the equivalent non-pregnant women.

A study by Walravens & Hambridge (1976) of 68 infants, showed no adverse effects at a level of 5.8 mg zinc/L of infant formula fed for 6 months. This would translate to a NOAEL of 4.5 mg/day at 0.78 L milk per day. A UF of 1 was applied, given the length and quality of the study and the fact that there is no evidence of harm from intakes of formula at 5.8 mg zinc/L. Rounding down, a UL of 4 mg was therefore set for infants of 0-6 months. As there were no data for older children and adolescents, this figure was adjusted on a body weight basis, for older infants, children and adolescents and values rounded down. Lind et al (2003) showed in a double-blind RCT that plasma copper does not differ between infants receiving 10 mg Zn/day or placebo. However Bhandari et al (2002) reported lower copper levels in children of 6-12 month given 10 mg zinc/day and those of 1-2.5 years given 20 mg/day over 4 months.

Baer MT, King JC. Tissue zinc levels and zinc excretion during experimental zinc depletion in young men. Am J Clin Nutr 1984;39:556-70.

Bhandari N, Bahl R, Taneja S, Strand T, Molbak K, Ulvik RJ, Sommerfelt H, Bhan MK. Substantial reduction in severe diarrheal morbidity by daily zinc supplementation in young north Indian children. Pediatr 2002;109:E86.

Cousins RJ. Theoretical and practical aspects of zinc uptake and absorption. Adv Exp Med Biol 1989;249:3-12.

Davidsson L, MacKenzie J, Kastenmayer P, Aggett PJ, Hurrell RF. Zinc and calcium apparent absorption from an infant cereal: A stable isotope study in healthy infants. Br J Nutr 1996;75:291-300.

Fairweather-Tait SAJ, Wharf SJ, Fox TE. Zinc absorption in infants fed iron-fortified weaning food. Am J Clin Nutr 1995;62;785-9.

Fischer PWF, Giroux A, L’Abbe MR. Effect of zinc supplementation on copper excretion and retention in men. Am J Clin Nutr 1984;40:743-6.

Food and Nutrition Board: Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, manganese, Molybdenum, Nickel, Silicon, Vanadium and Zinc. Washington, DC: National Academy Press, 2001.

Fung EB, Ritchie LD, Woodhouse LR, Roehl R, King JC. Zinc absorption in women during pregnancy and lactation Am J Clin Nutr 1997;66:80-8.

Hambidge KM, Krebs NF, Jacobs MA, Favier A, Guyette L, Ikle DN. Zinc nutrition status during pregnancy: A longitudinal study. Am J Clin Nutr 1983;37:429-42.

Hambidge KM, Krebs NF, Lilly JR, Zerbe GO. Plasma and urine zinc in infants and children with extrahepatic biliary atresia. J Pediatr Gastrenterol Nutr 1987;6:872-7.

International Zinc Nutrition Consultative Group (IZiNCG). Hotz C and Brown K eds. Assessment of the risk of zinc deficiency in populations and options for its control. Technical Document #1. Food and Nutrition Bulletin 2004;25: S99-S199.

King JC, Turland JR. Human zinc requirements. In: Mills CE, ed. Zinc in Human Biology, London: Springer-Verlag, 1989. Pp 335-50.

Krebs NF, Hambridge KM. Zinc requirements and zinc intakes of breast-fed infants. Am J Clin Nutr 1986;43:2988-92.

Krebs NF, Reidinger CJ, Hartley S, Robertson AD, Hambridge KM. Zinc supplementation during lactation: effects on maternal status and milk zinc concentrations. Am J Clin Nutr 1995;61:1030-6.

Krebs NF, Reidinger CJ, Miller LV, Hambridge KM. Zinc homeostasis in breast-fed infants. Pediatr Res 1996;39:661-5.

Lind T, Lonnerdal B, Stenlund H, Ismail D, Seswandhana R, Ekstrom E-C, Persson L-A. A community-based, randomized controlled trial of iron and/or zinc supplementation of Indonesian infants – interactions between iron and zinc. Am J Clin Nutr 2003;77:
883-90.

Lonnerdal B, Bell JG, Hendrikkx AG, Burns RA, Keen CL. Effect of phytate removal on zinc absorption from soy formula. Am J Clin Nutr 1988;48:1301-6.

Lonnerdal B. Intestinal absorption of zinc. In: Mills CF ed. Zinc in Human Biology. New York: Springer-Verlag, 1989. Pp 33-55.

McKenna AA, Illich JZ, Andon MB, Wang C, Matkovic V. Zinc balance in adolescent females consuming a low-or high-calcium diet. Am J Clin Nutr 1997;65:1460-4.

O’Brien KO, Zavaleta N, Caulfield LE, Wen J, Abrams SA. Prenatal iron supplements impair zinc absorption in pregnant Peruvian women. J Nutr 2000;130:2251-5.

Roth HP, Kirchgessner M. Utilization of zinc from picolinic or citric acid complexes in relation to dietary protein sources in rats. J Nutr 1985;115:1641-9.

Samman S, Roberts DCK. The effect of zinc supplements on copper levels and the reported symptoms in healthy volunteers. Med J Aust 1988;146:246-9.

Sandstrom B, Cederblad A, Lonnerdal B. Zinc absorption from human milk, cow’s milk and infant formulas. Am J Dis Child 1983;137:726-9.

Sandstrom B, Lonnerdal B. Promoters and antagonists of zinc absorption. In: Mills CF ed. Zinc in Human Biology. New York: Springer-Verlag, 1989. Pp 57-78

Swanson CA, King JC. Zinc and pregnancy outcomes. Am J Clin Nutr 1987;46:763-71.

Walravens PA, Hambridge KM. Growth of infants fed a zinc supplemented formula. Am J Clin Nutr 1976;29:1114-21.

Wood RJ, Zheng JJ. High dietary calcium intakes reduce zinc absorption and balance in humans. Am J Clin Nutr 1997;65:1803-9.

Yadrick MK, Kenney MA, Winterfeldt EA. Iron, copper and zinc status: response to supplementation with zinc or zinc and iron in adult females. Am J Clin Nutr 1989;49:145-50.

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