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Zinc

What is zinc?

Zinc is a mineral that is an essential nutrient to human life and health.

The chemical symbol for zinc is Zn.

Zinc Functions

Some of the zinc functions in the human body [1]:

  • Protein and DNA synthesis
  • Development of organs and growth
  • Immunity
  • Wound healing
  • Proper sense of taste and smell

How much zinc do you need per day?

The Recommended Dietary Allowance (RDA) for zinc for adults is 8-11 mg/day [1].

Chart 1. Foods High in Zinc
PLANT FOODS Zinc (mg)
Cereals ready-to-eat, prepared (1 cup, 237 mL) 0-15
Nuts, seeds (1 oz, 28 g) 1-2
Chickpeas, kidney beans, lentils, peas (1/2 cup, 120 mL) 1-2
Cornmeal (1 cup, 237 mL) 1.5
Rice, white/brown (1 cup, 237 mL) 1
Bread, whole-wheat (2 slices, 60 g) 1
ANIMAL FOODS
Oysters (3 oz, 85 g) 30-77
Beef, bison, lamb, pork, veal (3 oz, 85 g) 2-10
Crabs (3 oz, 85 g) 2-6
Chicken, turkey (3 oz, 85 g) 2-4
Mollusks (3 oz, 85 g) 3
Cheese (2  oz, 57 g) 2
Milk (1 cup, 237 mL) 1

Chart 1 source: USDA.gov [2] All listed foods are ready to eat.

Human breast milk contains 1.7 mg of zinc per liter [2]. Breast milk provides sufficient zinc for the first 6 months of life [1]. An Adequate (AI) for zinc for 0-6 months old infants is 2 mg/day, and Recommended Dietary Allowance (RDA) for 7-12 months old infants is 3 mg/day [1].

Zinc Absorption

Zinc from animal foods is absorbed better than from plant foods, which contain phytates that reduce zinc absorption in the small intestine. In long-term studies, phytate from foods did not significantly affect the bioavailability of zinc, though [35].

Zinc Deficiency: Causes, Symptoms

In the Western world, zinc deficiency is rare; it can be caused by [1]:

  • Poor zinc absorption due to:
    • Celiac disease, Crohn’s disease, short bowel syndrome (SBS) after surgical bowel removal, fructose malabsorption [33], gastric bypass (bariatric surgery for weight loss) [3,4]
    • Medications: tetracycline, penicillamin, high doses of iron supplements
    • Chronic excessive alcohol intake
    • Diabetes
    • Chronic diarrhea of any cause
    • Chronic liver disease or other chronic disease
    • A genetic disorder called acrodermatitis enteropathica
  • Excessive needs for zinc in:
    • Cancer
    • Sickle cell anemia
  • Excessive zinc loss due to:
    • Diuretics
    • Chronic kidney disease

In poor areas of Africa, common causes of zinc deficiency are [1]:

  • Starvation
  • Chronic diarrhea

Who else is at increased risk of zinc deficiency?

  • Strict vegetarians (vegans). Soaking beans until they sprout before cooking reduces phytate content and thus increases zinc absorption from beans. Baker’s yeast breaks down some phytate, so zinc from leavened breads is better absorbed than from unleavened ones.
  • Pregnant and breastfeeding women
  • Exclusively breastfed infants after 6 months of age
  • Reference: [1]

Symptoms of zinc deficiency include slow growth (adolescent nutritional dwarfism), delayed sexual development, impotence in men, increased susceptibility to infections, diarrhea, weight loss, slow wound healing, loss of the sense of taste and smell, hair loss, skin lesions and night blindness (since zinc hampers vitamin A release from the liver), depression [5,6].

Zinc Supplements

Supplements without prescription (over-the-counter):

  • Zinc acetate, zinc gluconate, zinc-histidine, zinc picolinate and zinc sulfate in the form of tablets, capsules, lozenges, ointments are available as dietary supplements.
  • Zinc may be also included in multivitamin/mineral supplements.

There are no confirmed differences in effectiveness of different zinc supplements [1]. In one study zinc-histidine supplements were absorbed better than other forms, though [34].

Zinc Benefits

Zinc supplements are EFFECTIVE in [7]:

  • Prevention and treatment of zinc deficiency
  • Treatment of acrodermatitis enteropathica [8]

Zinc supplements are POSSIBLY EFFECTIVE for [7]:

  • Reducing diarrhea in malnourished children or in children who have low zinc levels [22]
  • Increasing vitamin A levels in underfed children or in children with low zinc levels [32]
  • Promotion of growth and reducing death children in areas with common zinc deficiency [14]
  • Prevention and treatment of pneumonia in undernourished children in developing countries [13]
  • Treatment of Wilson’s disease [30]

Zinc supplements are POSSIBLY INEFFECTIVE in prevention or treatment of AIDS diarrhea-wasting syndrome, arthritis, cataracts, inflammatory bowel disease, malaria, ringing in the ears (tinnitus) and flu, or in increasing birth weight and gestation time in infants born to HIV-infected women, or in raising blood iron levels in pregnant women [7].

There is INSUFFICIENT EVIDENCE about the effectiveness of oral zinc supplements in shortening  of duration and decreasing  severity of common cold (when used as a lozenge within 24 hours of the cold onset) [19,20]. Intranasal zinc ointments should be avoided, since they may permanently damage the sense of smell. Zinc does not seem to prevent common cold.

There is INSUFFICIENT EVIDENCE about zinc effectiveness in prevention or treatment of acne [30], age-related macular degeneration (AMD) [15], Alzheimer’s disease, anorexia nervosa [28,29], asthma, attention deficit hyperactive disorder (ADHD) [26], bad breath [17,30], boils [30], cancer, canker sores [30], celiac disease [30], dandruff [30], diabetes mellitus type 2 [12], eczema [18], foot ulcers [30], growth [30], gum disease (gingivitis) [30], hair loss [30], hepatic encephalopathy [30], hepatitis [30], high cholesterol [30], HIV/AIDS [30], hypogeusia (abnormal sense of taste in dialysis patients) [30], hypothyroidism [30], infertility [30], inflammatory bowel disease (Crohn’s disease, ulcerative colitis) [30], leg ulcers (venous or arterial) [10], leprosy [27], malaria [30], male sexual problems, measles [11], menstrual cramps [30], middle ear infections [21], mood disorders [30], mouth sores caused by radiation [30], muscle cramps [30], osteoporosis [25], parasites [30], prostatitis [30], psoriasis [30], rheumatoid arthritis, [30], sickle cell anemia [16], stomach ulcers [31], stress [30], thalassemia [23], ulcerative colitis [7] preterm births [9], respiratory tract infections [30], ringing in the ears (tinnitus) [30], vaginitis [30], warts [30], or improving exercise performance, immunity [30] or motor or mental development in children [24].

Zinc Safety: Side Effects, Toxicity

Upper Tolerable Intake Level (UL)–the amount that should not cause side effects–for zinc for adults is 40 mg of zinc/day [1].

Acute side effects of zinc supplements include vomiting, diarrhea and headache. A single dose 20-30 grams of zinc may be fatal [1].

Chronic excessive zinc intake may result in low blood copper levels, increased susceptibility for infections, low blood copper and HDL cholesterol levels. Certain over-the-counter (OTC) zinc nasal gels and sprays may cause a permanent loss of the sense of smell [1,7]. Zinc may shorten life of patients with HIV/AIDS [7]. Taking 100 mg or more zinc/day may increase the risk of prostate cancer [7].

Zinc Deficiency Diagnosis

Zinc deficiency can be diagnosed from low blood zinc levels.

Zinc Interactions With Drugs and Nutrients

Substances that may decrease zinc absorption [1,8]:

  • Phytates in legumes and whole grains
  • High calcium intake from milk, tortilla made with lime, or calcium supplements may decrease zinc absorption in women after menopause (but not in premenopausal women)
  • Iron supplements in doses greater than 25 mg
  • Penicillamine (a copper binder used in Wilson’s disease) and DTPA (an iron binder used in iron overdose)
  • Antibiotics, such as tetracycline or ciprofloxacin
  • Diuretics, such as chlorthalidone and hydrochlorothiazide, increase zinc excretion
  • Sodium valproate (anticonvulsant)

Zinc supplements in doses greater than 50 mg/day may reduce the absorption and effectiveness of copper supplements, penicillamine and antibiotics, such as ciprofloxacin and tetracycline [8].

Zinc deficiency can decrease the bioavailability of vitamin A [8].

  1. Zinc National Institute of Health, Office of Dietary Supplements
  2. List of foods high in zinc US Department of Agriculture
  3. Shankar P et al, 2010, Micronutrient deficiencies after bariatric surgery (PubMed)
  4. Belin LTC R et al, 2011, Benchmarking Best Practices in Weight Loss Surgery PubMed Central
  5. Roozbeh J et al, 2011, Association of zinc deficiency and depression in the patients with end-stage renal disease on hemodialysis PubMed
  6. Cope EC et al, 2010, Role of zinc in the development and treatment of mood disorders PubMed
  7. Zinc MedlinePlus
  8. Zinc Linus Pauling Institute
  9. Ota E et al, 2015, Zinc supplementation for improving pregnancy and infant outcome Cochrane
  10. Wilkinson EAJ, 2014, Oral zinc supplements for treating leg ulcers Cochrane
  11. Awotiwon AA, 2015, Zinc supplementation for the treatment of measles in children Cochrane
  12. El Dib R et al, 2015, Zinc supplementation for the prevention of type 2 diabetes mellitus Cochrane
  13. Lassi ZS et al, 2012, Zinc supplementation for the prevention of pneumonia in children aged two to 59 months Cochrane
  14. Mayo-Wilson E et al, 2014, Zinc supplementation for preventing death and disease, and for growth, in children aged six months to 12 years of age
    Cochrane
  15. Evans JR et al, 2012, Antioxidant vitamins and mineral supplements to slow down the progression of age-related macular degeneration Cochrane
  16. Nagalla S et al, 2012, Drugs that aim to reduce the loss of water from red blood cells in people with sickle cell disease Cochrane
  17. Fedorowicz Z et al, 2008, Mouthrinses for the treatment of halitosis Cochrane
  18. Bath-Hextall FJ et al, 2012, Dietary supplements for established atopic eczema in adults and children Cochrane
  19. 2010, The Flu, the Common Cold, and Complementary Health Approaches National Center for Complementary and Integrative Health
  20. Science M et al, 2012, Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials PubMed Central
  21. Gulani A et al, 2014, Zinc supplements for preventing middle ear infections Cochrane
  22. Lazzerini M et al, 2013, Oral zinc supplementation for treating diarrhoea in children Cochrane
  23. Swe K et al, 2013, Zinc supplements for thalassaemia and sickle cell disease Cochrane
  24. Gogia S et al, 2012, Zinc supplementation for mental and motor development in children Cochrane
  25. Lowe NM et al, 2002, Is there a potential therapeutic value of copper and zinc for osteoporosis? Cambridge Journals
  26. Ghanizadeh A et al, 2013, Zinc for treating of children and adolescents with attention-deficit hyperactivity disorder: a systematic review of randomized controlled clinical trials PubMed
  27. Mathur NK et al, 1984, Oral zinc as an adjunct to dapsone in lepromatous leprosy PubMed
  28. 2004, Eating Disorders: Core Interventions in the Treatment and Management of Anorexia Nervosa, Bulimia Nervosa and Related Eating Disorders National Center for Biotechnology Information
  29. Fitzpatrick KK et al, 2011, Anorexia nervosa PubMed Central
  30. Zinc Mayo Clinic
  31. Zinc University of Maryland, Medical Center
  32. Christian P et al, 1998, Interactions between zinc and vitamin A: an update The American Journal of Clinical Nutrition
  33. Ledochowski M et al, 2001, Decreased Serum Zinc in Fructose Malabsorbers ClinChem
  34. Schölmerich J et al, 1987, Bioavailability of zinc from zinc-histidine complexes. Comparison with zinc sulfate in healthy men American Journal of Clinical Nutrition
  35. 2011, GRAS Notification for Phytic Acid (50% Solution) US Food and Drug Administration

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