Journal of Family Practice. November Zinc in Diet. November 6, Cleveland Clinic. March 10, Journal of Reproduction and Infertility. April—June Livingstone C. Zinc: Physiology, Deficiency, and Parenteral Nutrition.
Nutrition in Clinical Practice. June Saper RB, Rash R. Zinc: An Essential Macronutrient. American Family Physician. May 1, Zinc Fact Sheet for Health Professionals. July 10, Nutrients: Zinc, Zn mg.
October 22, Mayo Clinic. October 24, October 1, Common Colds: Protect Yourself and Others. Centers for Disease Control and Prevention. February 11, Zinc for Colds: The Final Word? Stomach pain and diarrhea are common symptoms of zinc toxicity. In some cases, severe gastrointestinal damage and bleeding can occur. Taking more zinc than the established UL may cause flu-like symptoms, such as fever, chills, cough, headache and fatigue These symptoms occur in many conditions, including other mineral toxicities.
Thus, diagnosing zinc toxicity can be difficult. Your doctor may need your detailed medical and dietary history, as well as blood tests, for a suspected mineral toxicity. Flu-like symptoms can occur due to toxic amounts of several minerals, including zinc. Lower levels put you at a higher risk of heart disease. The review also states that doses of 30 mg of zinc per day — lower than the UL for zinc — had no effects on HDL when taken for up to 14 weeks While several factors affect cholesterol levels, these findings are something to consider if you take zinc supplements regularly.
Zinc is important for your sense of taste. In fact, zinc deficiency can result in a condition called hypogeusia, a dysfunction in your ability to taste 1. Interestingly, zinc in excess of the recommended levels may also cause taste alterations, including a bad or metallic taste in your mouth.
Typically, this symptom is reported in studies investigating zinc lozenges cough drops or liquid supplements for treating the common cold. While some studies report beneficial results, the doses used are often well above the UL of 40 mg per day, and adverse effects are common 3.
Zinc plays a role in taste perception. Excess zinc may cause a metallic taste in your mouth, particularly if taken as a lozenge or liquid supplement. Over time, this can cause copper deficiency 2. Like zinc, copper is an essential mineral. It aids in iron absorption and metabolism, making it necessary for red blood cell formation.
It also plays a role in white blood cell formation Red blood cells transport oxygen through your body, while white blood cells are key players in your immune function. Zinc-induced copper deficiency is associated with several blood disorders 17 , 18 , 19 :. Regular doses of zinc above 40 mg per day can hinder copper absorption. This can result in copper deficiency, which is associated with several blood disorders. Although zinc plays an important role in immune system function, too much zinc can suppress your immune response This is usually a side effect of anemias and neutropenia, but it has also been shown to occur outside of zinc-induced blood disorders.
In test-tube studies, excess zinc reduced the function of T cells, a type of a white blood cell. T cells play a central role in your immune response by attaching to and destroying harmful pathogens 17 , 20 , A small study in 11 healthy men found a reduced immune response after they ingested mg of zinc twice a day for six weeks However, supplementing with mg of zinc three times a day for one month had mixed effects on older adults.
Some experienced a reduced immune response, while others had an enhanced response Taking zinc supplements in doses above the UL may suppress your immune response, leaving you more susceptible to illness and infections.
If you believe you may be experiencing zinc poisoning, contact your local poison control center immediately. Zinc poisoning is potentially life-threatening. You may be advised to drink milk , as the high amounts of calcium and phosphorus in it can help inhibit zinc absorption in the gastrointestinal tract. Activated charcoal has a similar effect Animal studies have established that zinc deficiency in early life interferes with normal brain development and cognitive functions reviewed in Several studies have reported on the effect of postnatal zinc supplementation on mental and motor development.
A Cochrane review of eight clinical trials found no evidence that postnatal zinc supplementation improves mental or motor development of infants and children from populations with presumably inadequate zinc status Adequate zinc intake is essential in maintaining the integrity of the immune system 62 , specifically for normal development and function of cells that mediate both innate neutrophils , macrophages , and natural killer cells and adaptive B- lymphocytes and T-lymphocytes immune responses Because pathogens also require zinc to thrive and invade, a well-established antimicrobial defense mechanism in the body sequesters free zinc away from microbes Another opposite mechanism consists in intoxicating intracellular microbes within macrophages with excess zinc Through weakening innate and adaptive immune responses, zinc deficiency diminishes the capacity of the body to combat pathogens 63, As a consequence, zinc-deficient individuals experience an increased susceptibility to a variety of infectious agents Diarrhea: Zinc promotes mucosal resistance to infections by supporting the activity of immune cells and the production of antibodies against invading pathogens 63, 64 , Therefore, a deficiency in zinc increases the susceptibility to intestinal infections and constitutes a major contributor to diarrheal diseases in children In turn, persistent diarrhea contributes to zinc deficiency and malnutrition Research indicates that zinc deficiency may also potentiate the effects of toxins produced by diarrhea-causing bacteria like E.
It is estimated that diarrheal diseases are responsible for the deaths of about , children under five years of age annually in low- and middle-income countries Zinc supplementation in combination with oral rehydration therapy has been shown to significantly reduce the duration and severity of acute and persistent childhood diarrhea and to increase survival in a number of randomized controlled trials Zinc supplementation also reduced the duration of persistent diarrhea in children by more than half a day 5 trials; children Pneumonia: Pneumonia — caused by lower respiratory tract viral or bacterial infections LRTIs — accounts for nearly 1 million deaths among children annually, primarily in low-and middle-income countries Vaccinations against Haemophilus influenzae type B, pneumococcus, pertussis whooping cough , and measles can help prevent pneumonia However, it remains unclear whether supplemental zinc, in conjunction with antibiotic therapy, is beneficial in the treatment of pneumonia.
A meta-analysis of five trials 1, participants found no improvement when zinc was used as an adjunct to antibiotic treatment in children with pneumonia There was, however, evidence that supplemental zinc reduced the risk of pneumonia-related mortality 3 trials; 1, participants Malaria: Early studies have indicated that zinc supplementation may reduce the incidence of clinical attacks of malaria in children However, a six-month trial in more than West African children did not find any difference in the frequency or severity of malaria episodes between children supplemented with zinc and those given a placebo Another randomized controlled trial reported that zinc supplementation did not benefit preschool-aged children with acute, uncomplicated malaria There is also little evidence to suggest that zinc supplementation could reduce the risk of malaria-related mortality in children Inadequate zinc status in elderly subjects is not uncommon and is thought to exacerbate the age-related decline in immune function In one study, low serum zinc concentrations in nursing home residents were associated with higher risks of pneumonia and pneumonia-related and all-cause mortality Trials examining the effects of zinc supplementation on immune function in middle-aged and elderly adults have given mixed results reviewed in Some studies showed mixed or no effects of zinc supplementation on parameters of immune function However, zinc supplementation was found to have a positive impact on certain aspects of immune function that are affected by zinc deficiency, such as the decline in T-cell a type of lymphocyte function Further, zinc supplementation had no effect on various immune parameters, including markers of inflammation , measures of granulocyte and monocyte phagocytic capacity, or cytokine production by activated monocytes The number of circulating T-cells was also significantly increased in those who took the micronutrient supplement with the higher versus low dose of zinc More research is warranted before zinc supplementation could be recommended to older adults, especially those with no symptoms of declining immunity.
Nonetheless, the high prevalence of zinc deficiency among institutionalized elderly adults should be addressed and would likely improve the performance of their immune systems There is a close relationship between zinc and insulin action.
Zinc is released with the hormone when blood glucose concentrations increase Zinc is also understood to stimulate glucose uptake and metabolism by insulin-sensitive tissues through triggering the intracellular insulin signaling pathway Both NHS and ALSWH studies also reported a reduced risk of diabetes with higher versus lower zinc-to- heme iron ratios in the diet 97, 98 , although the significance is unclear as nonheme iron, rather than heme iron, is known to interfere with dietary zinc absorption see Nutrient interactions.
Heme iron may be an indicator of red meat consumption, which has been positively associated with the risk of type 2 diabetes Another recent prospective cohort study, the Malmo Diet and Cancer Study in 26, middle-aged Swedish participants followed for 19 years, found an increased risk of diabetes with higher dietary zinc intakes yet a lower risk of diabetes in zinc supplement users versus non-users and in those with a higher zinc-to-iron intake ratio The authors reported a stronger inverse association between zinc-to-iron intake ratio and risk of diabetes among obese participants carrying a specific SLC30A8 genotype The results of a few short-term intervention studies suggest that zinc supplementation may improve glucose handling in subjects with prediabetes.
A systematic review identified three short trials 4 to 12 weeks conducted in adults with prediabetes and found little evidence of an improvement in insulin resistance with zinc supplementation Similar observations were made in another recent trial in Sri Lankan randomized to receive daily supplementation with zinc 20 mg of elemental zinc or a placebo for one year Supplemental zinc improved zinc status and measures of glycemic control Large-scale, long-term studies are necessary to provide definite conclusions regarding the potential benefit of zinc supplementation in subjects at risk of type 2 diabetes.
Doses of supplemental zinc in many of the below-mentioned clinical trials exceeded the tolerable upper intake level UL. Such high intake of supplemental zinc may lead to adverse health effects with prolonged use see Safety. The protein, ATP7B, is responsible for the excretion of hepatic copper into the biliary tract, and its impairment in Wilson's disease results in an increased concentration of 'free' copper i. This inherited condition is progressive and fatal if untreated.
Patients presenting without symptoms can be treated with maintenance therapeutic doses of a chelating agent or with zinc Zinc-induced metallothionein in the intestinal mucosa binds copper and prevents its absorption see Nutrient interactions.
There is growing evidence to suggest that zinc salts are a safer, much cheaper, and efficacious alternative to metal-chelating agents — which have been associated with a worsening of symptoms during the initial phase of treatment in some patients The use of zinc is advocated as safe and efficacious in both pediatric , and adult patients There is no proven treatment for common cold The use of zinc lozenges within 24 hours of the onset of cold symptoms, and continued intake every two to three hours while awake until symptoms resolve, have been advocated for reducing the duration of the common cold Several clinical trials examining the effect of zinc have been published to date.
A systematic review and meta-analysis of 13 randomized controlled trials reported that zinc supplementation in the form of lozenges or syrup shortened the duration of cold symptoms, but there was significant heterogeneity inconsistent effects across the included studies for the primary outcomes A Cochrane review confirmed that oral zinc administrated within 24 hours of symptom onset could reduce the duration of cold symptoms 14 trials, 1, participants The pooled analysis of five trials found no evidence of an effect of oral zinc on the severity of cold symptoms.
The analysis of secondary trial outcomes suggested a faster resolution of specific cold symptoms cough, nasal congestion, nasal drainage, sore throat and a lower proportion of participants exhibiting cold symptoms after seven days of treatment in zinc- versus placebo -supplemented participants Inconsistent findings among trials have been partly attributed to different amounts of zinc released from various forms used in the lozenges particularly zinc acetate and zinc gluconate , It has been argued that the unpleasant taste of zinc gluconate forming complexes with carbohydrates may have led to poor compliance, thereby explaining negative trial results , With numerous well-controlled trials and meta-analyses, the efficacy of zinc lozenges or syrup in treating common cold symptoms is no longer questionable.
However, many supplemental zinc formulations available over-the-counter have been found to release zero zinc ions i. Bad taste and nausea were the most frequent adverse effects reported in therapeutic trials Use of zinc lozenges for prolonged periods e.
Intranasal zinc preparations, designed to be applied directly to the nasal epithelium cells lining the nasal passages , are marketed as over-the-counter cold remedies. While two placebo -controlled trials found that intranasal zinc gluconate modestly shortened the duration of cold symptoms , , another one found intranasal zinc to be of no benefit The pooled analysis of these three trials showed no overall benefit of intranasal zinc on the risk of still experiencing cold symptoms by day 3 The existence of a mouth-nose biologically close electric circuit BCEC has been proposed to explain the efficacy of oral rather than intranasal zinc delivery Of serious concern are several case reports of individuals experiencing loss of the sense of smell anosmia after using intranasal zinc as a cold remedy Since zinc-associated anosmia may be irreversible, intranasal zinc preparations should be avoided.
The macula is the portion of the retina in the back of the eye involved with central vision. Zinc is hypothesized to play a role in the development of AMD for several reasons: 1 zinc is found at high concentrations in the part of the retina affected by AMD, 2 retinal zinc content has been shown to decline with age, and 3 the activities of some zinc-dependent retinal enzymes have been shown to decline with age.
To date, prospective cohort studies have shown limited evidence suggesting an association between dietary zinc intake and the incidence of AMD Yet a later trial using the same dose and duration found no benefit to patients with a more advanced form of AMD in one eye Small trials have generally not reported a protective effect of vitamin and mineral supplementation on AMD , There was, however, no effect of AREDS formulation on the risk of developing central geographic atrophy A recent meta-analysis of five trials including the original AREDS study confirmed the protective effect of supplemental zinc against neovascular and advanced AMD Patients, especially smokers and those with vascular disease, are advised to discuss with their physician the benefits versus potential harms that could be associated with the long-term use of high-dose antioxidant vitamins and carotenoids Poor glycemic control and frequent urination in patients with diabetes mellitus may be driving urinary loss of zinc and contribute to marginal zinc deficiency , Supplemental zinc also reduced the proportion of glycated hemoglobin HbA1c in two trials conducted in zinc-deficient participants, yet not in four studies including participants without zinc deficiency Patients with type 2 diabetes should ensure that their diet provides enough zinc to cover their needs, especially if their blood glucose is poorly controlled.
Gestational diabetes mellitus is defined as hyperglycemia that is first diagnosed during pregnancy. The condition is associated with an increased risk for adverse pregnancy outcomes A group of investigators in Iran conducted two small randomized , placebo -controlled trials to examine the effect of zinc supplementation in pregnant women with gestational diabetes.
Similar improvements of markers of glycemic control were reported in another placebo-controlled trial that randomized pregnant women with gestational diabetes to receive zinc 4 mg together with magnesium mg , calcium mg , and vitamin D IU twice a day for six weeks There was also some evidence suggesting that supplemental zinc might help correct other metabolic disorders e. Sufficient zinc is essential to maintain immune system function, and HIV -infected individuals are particularly susceptible to zinc deficiency.
In HIV-infected patients, low serum zinc concentrations have been associated with disease progression and increased mortality , A systematic review that identified three randomized controlled trials in primarily resource-poor settings concluded that zinc supplementation was safe and efficacious in reducing opportunistic infections in HIV-positive adults Evidence of benefits of zinc supplementation in HIV-positive pregnant women and children is very limited.
There was evidence showing a reduction in the incidence of watery diarrhea in zinc-supplemented children compared to those taking a placebo, yet no differences in the incidence of pneumonia , ear infection, or upper respiratory tract infection While zinc supplementation during pregnancy and infancy is recommended in populations likely to be zinc deficient 43 , 71 , 75 , its use in HIV infection management requires further investigation Additional evidence is needed to confirm whether zinc supplementation could play a role in stabilizing cognitive deficits in older adults with dementia.
A data analysis of the Boston Area Community Health BACH survey, including 3, participants ages, years , reported higher odds of depression symptoms in women but not in men in the lowest versus highest quartiles of total median values, 8. The possibility that zinc could play a role in preventing or alleviating depression has been explored in two trials conducted by one research group. The data from these trials were analyzed following a per-protocol approach i. Zinc supplementation improved score-based measures of therapeutic response and remission after six weeks but only when the analysis was restricted to participants resistant to imipramine.
There was, however, no evidence of an effect of zinc after 12 weeks Sepsis is accompanied by changes in zinc homeostasis characterized in particular by a decrease in serum zinc concentration and an increase in liver zinc concentration Such a mechanism has been described for other transition metals, including iron and manganese However, lower serum zinc concentrations in critically ill patients at high risk of organ failure have been associated with recurrent sepsis episodes and poorer outcomes , A systematic review identified four trials that examined the effect of zinc supplementation in newborns with sepsis Zinc supplementation was found to result in decreased inflammation and better neurological development , Three out of four trials that examined the rate of mortality showed no effect of zinc supplementation , , Shellfish, beef, and other red meats are rich sources of zinc; nuts and legumes are relatively good plant sources of zinc.
Zinc bioavailability the fraction of zinc retained and used by the body is relatively high in meat, eggs, and seafood because of the relative absence of compounds that inhibit zinc absorption and the presence of sulfur-containing amino acids cysteine and methionine that improve zinc absorption.
Zinc in whole-grain products and plant proteins is less bioavailable due to their relatively high content of phytate, which inhibits zinc absorption The enzymatic action of yeast reduces the level of phytate in foods; therefore, leavened whole-grain breads have more bioavailable zinc than unleavened whole-grain breads. National dietary surveys in the US estimate that average dietary zinc intake from naturally and fortified food is about The zinc content of some foods relatively rich in zinc is listed in Table 2 in milligrams mg.
A number of zinc supplements are commercially available, including zinc acetate, zinc gluconate, zinc picolinate, and zinc sulfate. Zinc picolinate has been promoted as a more absorbable form of zinc, but there are few data to support this idea in humans.
Limited work in animals suggests that increased intestinal absorption of zinc picolinate may be offset by increased elimination Isolated outbreaks of acute zinc toxicity have occurred as a result of the consumption of food or beverages contaminated with zinc released from galvanized containers.
Signs of acute zinc toxicity are abdominal pain, diarrhea, nausea, and vomiting. Single doses of to mg of zinc usually induce vomiting. Metal fume fever has been reported after the inhalation of zinc oxide fumes. Specifically, profuse sweating, weakness, and rapid breathing may develop within eight hours of zinc oxide inhalation and persist for 12 to 24 hours after exposure is terminated 6 , The major consequence of long-term consumption of excessive zinc is copper deficiency.
Intranasal zinc is known to cause a loss of the sense of smell anosmia in laboratory animals , and there have been several case reports of individuals who developed anosmia after using intranasal zinc gluconate Since zinc-associated anosmia may be irreversible, the use of zinc nasal gels and sprays should be avoided. The use of zinc supplements decreases the absorption of certain medications, including cephalexin Keplex and penicillamine Cuprimine, Depen , as well as the antiretroviral drugs atazanavir Reyataz and ritonavir Norvir Concomitant administration of zinc supplements with certain medications like tetracycline and quinolone antibiotics may decrease the absorption of both zinc and the medications, potentially reducing drug efficacy.
Taking zinc supplements and these medications at least two hours apart should prevent this interaction. The therapeutic use of metal-chelating agents, such as penicillamine used to treat copper overload in Wilson's disease and diethylenetriamine pentaacetate DTPA; used to treat iron overload , has resulted in severe zinc deficiency.
Anticonvulsant drugs, especially sodium valproate, may also precipitate zinc deficiency. Prolonged use of diuretics may increase urinary zinc excretion , resulting in increased loss of zinc. Because supplemental zinc can lower blood glucose , those taking anti-diabetic agents are advised to use zinc supplements with caution. Although the requirement for zinc is not known to be higher for older adults, many have inadequate dietary zinc intakes , A reduced capacity to absorb zinc, increased likelihood of disease states that alter zinc utilization, and increased use of drugs that decrease zinc bioavailability may all contribute to an increased risk of mild zinc deficiency in older adults.
Adequate dietary intake of zinc is essential for older adults because the consequences of mild zinc deficiency, such as impaired immune system function, are especially relevant to maintenance of their health. Originally written in by: Jane Higdon, Ph. Updated in December by: Jane Higdon, Ph. Updated in October by: Victoria J. Drake, Ph. Updated in June by: Victoria J. Updated in February by: Barbara Delage, Ph.
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