Prevalence of Zinc Deficiency and the Effect of Zinc Supplementation on the Prevention of Acute Respiratory Infections

Dietary zinc supplements: beneficial health effects and application in food, medicine and animals

Zinc, a crucial trace element is vital for the growth and development of humans. It is frequently described as 'the flower of life' and 'the source of intelligence'. Zinc supplements play a pivotal role in addressing zinc deficiency by serving as a vital source of this essential micronutrients, effectively replenishing depleted zinc levels in the body. In this paper, we first described the biological behavior of zinc in the human body and briefly described the physiological phenomena associated with zinc levels. The benefits and drawbacks of various zinc supplement forms are then discussed, with emphasis on the most recent zinc supplement formulations. Finally, the application of zinc supplements in food, medicine, and animal husbandry is further summarized. © 2024 Society of Chemical Industry.

Zinc for prevention and treatment of the common cold

BACKGROUND

The common cold is an acute, self-limiting viral respiratory illness. Symptoms include nasal congestion and mucus discharge, sneezing, sore throat, cough, and general malaise. Given the frequency of colds, they are a public health burden and a significant cause of lost work productivity and school absenteeism. There are no established interventions to prevent colds or shorten their duration. However, zinc supplements are commonly recommended and taken for this purpose.

OBJECTIVES

To assess the effectiveness and safety of zinc for the prevention and treatment of the common cold.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, CINAHL, and LILACS to 22 May 2023, and searched Web of Science Core Collection and two trials registries to 14 June 2023. We also used reference checking, citation searching, and contact with study authors to identify additional studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in children or adults that tested any form of zinc against placebo to prevent or treat the common cold or upper respiratory infection (URTI). We excluded zinc interventions in which zinc was combined with other minerals, vitamins, or herbs (e.g. a multivitamin, or mineral supplement containing zinc).

DATA COLLECTION AND ANALYSIS

We used the Cochrane risk of bias tool to assess risks of bias, and GRADE to assess the certainty of the evidence. We independently extracted data. When necessary, we contacted study authors for additional information. We assessed zinc (type and route) with placebo in the prevention and treatment of the common cold. Primary outcomes included the proportion of participants developing colds (for analyses of prevention trials only), duration of cold (measured in days from start to resolution of the cold), adverse events potentially due to zinc supplements (e.g. unpleasant taste, loss of smell, vomiting, stomach cramps, and diarrhoea), and adverse events considered to be potential complications of the common cold (e.g. respiratory bacterial infections).

MAIN RESULTS

We included 34 studies (15 prevention, 19 treatment) involving 8526 participants. Twenty-two studies were conducted on adults and 12 studies were conducted on children. Most trials were conducted in the USA (n = 18), followed by India, Indonesia, Iran, and Turkey (two studies each), and Australia, Burkina Faso, Colombia, Denmark, Finland, Tanzania, Thailand, and the UK (one study each). The 15 prevention studies identified the condition as either common cold (n = 8) or URTI (n = 7). However, almost all therapeutic studies (17/19) focused on the common cold. Most studies (17/34) evaluated the effectiveness of zinc administered as lozenges (3 prevention; 14 treatment) in acetate, gluconate, and orotate forms; gluconate lozenges were the most common (9/17). Zinc gluconate was given at doses between 45 and 276 mg/day for between 4.5 and 21 days. Five (5/17) lozenge studies gave acetate lozenges and two (2/17) gave both acetate and gluconate lozenges. One (1/17) lozenge study administered intranasal (gluconate) and lozenge (orotate) zinc in tandem for cold treatment. Of the 17/34 studies that did not use lozenges, 1/17 gave capsules, 3/17 administered dissolved powders, 5/17 gave tablets, 4/17 used syrups, and 4/17 used intranasal administration. Most studies were at unclear or high risk of bias in at least one domain. There may be little or no reduction in the risk of developing a cold with zinc compared to placebo (risk ratio (RR) 0.93, 95% CI 0.85 to 1.01; I2 = 20%; 9 studies, 1449 participants; low-certainty evidence). There may be little or no reduction in the mean number of colds that occur over five to 18 months of follow-up (mean difference (MD) -0.90, 95% CI -1.93 to 0.12; I2 = 96%; 2 studies, 1284 participants; low-certainty evidence). When colds occur, there is probably little or no difference in the duration of colds in days (MD -0.63, 95% CI -1.29 to 0.04; I² = 77%; 3 studies, 740 participants; moderate-certainty evidence), and there may be little or no difference in global symptom severity (standardised mean difference (SMD) 0.04, 95% CI -0.35 to 0.43; I² = 0%; 2 studies, 101 participants; low-certainty evidence). When zinc is used for cold treatment, there may be a reduction in the mean duration of the cold in days (MD -2.37, 95% CI -4.21 to -0.53; I² = 97%; 8 studies, 972 participants; low-certainty evidence), although it is uncertain whether there is a reduction in the risk of having an ongoing cold at the end of follow-up (RR 0.52, 95% CI 0.21 to 1.27; I² = 65%; 5 studies, 357 participants; very low-certainty evidence), or global symptom severity (SMD -0.03, 95% CI -0.56 to 0.50; I² = 78%; 2 studies, 261 participants; very low-certainty evidence), and there may be little or no difference in the risk of a change in global symptom severity (RR 1.02, 95% CI 0.85 to 1.23; 1 study, 114 participants; low-certainty evidence). Thirty-one studies reported non-serious adverse events (2422 participants). It is uncertain whether there is a difference in the risk of adverse events with zinc used for cold prevention (RR 1.11, 95% CI 0.84 to 1.47; I2 = 0%; 7 studies, 1517 participants; very low-certainty evidence) or an increase in the risk of serious adverse events (RR 1.67, 95% CI 0.78 to 3.57; I2 = 0%; 3 studies, 1563 participants; low-certainty evidence). There is probably an increase in the risk of non-serious adverse events when zinc is used for cold treatment (RR 1.34, 95% CI 1.15 to 1.55; I2 = 44%; 2084 participants, 16 studies; moderate-certainty evidence); no treatment study provided information on serious adverse events. No study provided clear information about adverse events considered to be potential complications of the common cold.

AUTHORS' CONCLUSIONS

The findings suggest that zinc supplementation may have little or no effect on the prevention of colds but may reduce the duration of ongoing colds, with an increase in non-serious adverse events. Overall, there was wide variation in interventions (including concomitant therapy) and outcomes across the studies, as well as incomplete reporting of several domains, which should be considered when making conclusions about the efficacy of zinc for the common cold.

Zinc supplementation for preventing mortality, morbidity, and growth failure in children aged 6 months to 12 years

BACKGROUND

Zinc deficiency is prevalent in low- and middle-income countries, and is considered a significant risk factor for morbidity, mortality, and linear growth failure. The effectiveness of preventive zinc supplementation in reducing prevalence of zinc deficiency needs to be assessed.

OBJECTIVES

To assess the effects of zinc supplementation for preventing mortality and morbidity, and for promoting growth, in children aged 6 months to 12 years.

SEARCH METHODS

A previous version of this review was published in 2014. In this update, we searched CENTRAL, MEDLINE, Embase, five other databases, and one trials register up to February 2022, together with reference checking and contact with study authors to identify additional studies.

SELECTION CRITERIA

Randomized controlled trials (RCTs) of preventive zinc supplementation in children aged 6 months to 12 years compared with no intervention, a placebo, or a waiting list control. We excluded hospitalized children and children with chronic diseases or conditions. We excluded food fortification or intake, sprinkles, and therapeutic interventions.

DATA COLLECTION AND ANALYSIS

Two review authors screened studies, extracted data, and assessed the risk of bias. We contacted study authors for missing information and used GRADE to assess the certainty of evidence. The primary outcomes of this review were all-cause mortality; and cause-specific mortality, due to all-cause diarrhea, lower respiratory tract infection (LRTI, including pneumonia), and malaria. We also collected information on a number of secondary outcomes, such as those related to diarrhea and LRTI morbidity, growth outcomes and serum levels of micronutrients, and adverse events.

MAIN RESULTS

We included 16 new studies in this review, resulting in a total of 96 RCTs with 219,584 eligible participants. The included studies were conducted in 34 countries; 87 of them in low- or middle-income countries. Most of the children included in this review were under five years of age. The intervention was delivered most commonly in the form of syrup as zinc sulfate, and the most common dose was between 10 mg and 15 mg daily. The median duration of follow-up was 26 weeks. We did not consider that the evidence for the key analyses of morbidity and mortality outcomes was affected by risk of bias. High-certainty evidence showed little to no difference in all-cause mortality with preventive zinc supplementation compared to no zinc (risk ratio (RR) 0.93, 95% confidence interval (CI) 0.84 to 1.03; 16 studies, 17 comparisons, 143,474 participants). Moderate-certainty evidence showed that preventive zinc supplementation compared to no zinc likely results in little to no difference in mortality due to all-cause diarrhea (RR 0.95, 95% CI 0.69 to 1.31; 4 studies, 132,321 participants); but probably reduces mortality due to LRTI (RR 0.86, 95% CI 0.64 to 1.15; 3 studies, 132,063 participants) and mortality due to malaria (RR 0.90, 95% CI 0.77 to 1.06; 2 studies, 42,818 participants); however, the confidence intervals around the summary estimates for these outcomes were wide, and we could not rule out a possibility of increased risk of mortality. Preventive zinc supplementation likely reduces the incidence of all-cause diarrhea (RR 0.91, 95% CI 0.90 to 0.93; 39 studies, 19,468 participants; moderate-certainty evidence) but results in little to no difference in morbidity due to LRTI (RR 1.01, 95% CI 0.95 to 1.08; 19 studies, 10,555 participants; high-certainty evidence) compared to no zinc. There was moderate-certainty evidence that preventive zinc supplementation likely leads to a slight increase in height (standardized mean difference (SMD) 0.12, 95% CI 0.09 to 0.14; 74 studies, 20,720 participants). Zinc supplementation was associated with an increase in the number of participants with at least one vomiting episode (RR 1.29, 95% CI 1.14 to 1.46; 5 studies, 35,192 participants; high-certainty evidence). We report a number of other outcomes, including the effect of zinc supplementation on weight and serum markers such as zinc, hemoglobin, iron, copper, etc. We also performed a number of subgroup analyses and there was a consistent finding for a number of outcomes that co-supplementation of zinc with iron decreased the beneficial effect of zinc.

AUTHORS' CONCLUSIONS

Even though we included 16 new studies in this update, the overall conclusions of the review remain unchanged. Zinc supplementation might help prevent episodes of diarrhea and improve growth slightly, particularly in children aged 6 months to 12 years of age. The benefits of preventive zinc supplementation may outweigh the harms in regions where the risk of zinc deficiency is relatively high.

The Mechanisms of Zinc Action as a Potent Anti-Viral Agent: The Clinical Therapeutic Implication in COVID-19

The pandemic of COVID-19 was caused by a novel coronavirus termed as SARS-CoV2 and is still ongoing with high morbidity and mortality rates in the whole world. The pathogenesis of COVID-19 is highly linked with over-active immune and inflammatory responses, leading to activated cytokine storm, which contribute to ARDS with worsen outcome. Currently, there is no effective therapeutic drug for the treatment of COVID-19. Zinc is known to act as an immune modulator, which plays an important role in immune defense system. Recently, zinc has been widely considered as an anti-inflammatory and anti-oxidant agent. Accumulating numbers of studies have revealed that zinc plays an important role in antiviral immunity in several viral infections. Several early clinical trials clearly indicate that zinc treatment remarkably decreased the severity of the upper respiratory infection of rhinovirus in humans. Currently, zinc has been used for the therapeutic intervention of COVID-19 in many different clinical trials. Several clinical studies reveal that zinc treatment using a combination of HCQ and zinc pronouncedly reduced symptom score and the rates of hospital admission and mortality in COVID-19 patients. These data support that zinc might act as an anti-viral agent in the addition to its anti-inflammatory and anti-oxidant properties for the adjuvant therapeutic intervention of COVID-19.

The Association between Vitamin D and Zinc Status and the Progression of Clinical Symptoms among Outpatients Infected with SARS-CoV-2 and Potentially Non-Infected Participants: A Cross-Sectional Study

Vitamin D and zinc are important components of nutritional immunity. This study compared the serum concentrations of 25-hydroxyvitamin D (25(OH)D) and zinc in COVID-19 outpatients with those of potentially non-infected participants. The association of clinical symptoms with vitamin D and zinc status was also examined. A checklist and laboratory examination were applied to collect data in a cross-sectional study conducted on 53 infected outpatients with COVID-19 and 53 potentially non-infected participants. Serum concentration of 25(OH)D were not significantly lower in patients with moderate illness (19 ± 12 ng/mL) than patients with asymptomatic or mild illness (29 ± 18 ng/mL), with a trend noted for a lower serum concentration of 25(OH)D in moderate than asymptomatic or mild illness patients (p = 0.054). Infected patients (101 ± 18 µg/dL) showed a lower serum concentration of zinc than potentially non-infected participants (114 ± 13 µg/dL) (p = 0.01). Patients with normal (odds ratio (OR), 0.19; p ≤ 0.001) and insufficient (OR, 0.3; p = 0.007) vitamin D status at the second to seventh days of disease had decreased OR of general symptoms compared to patients with vitamin D deficiency. This study revealed the importance of 25(OH)D measurement to predict the progression of general and pulmonary symptoms and showed that infected patients had significantly lower zinc concentrations than potentially non-infected participants.

A comprehensive insight into the role of zinc deficiency in the renin-angiotensin and kinin-kallikrein system dysfunctions in COVID-19 patients

Hypozincemia is prevalent in severe acute respiratory syndrome coronavirus-2 (SARS-COV-2)-infected patients and has been considered as a risk factor in severe coronavirus disease-2019 (COVID-19). Whereas zinc might affect SARS-COV-2 replication and cell entry, the link between zinc deficiency and COVID-19 severity could also be attributed to the effects of COVID-19 on the body metabolism and immune response. Zinc deficiency is more prevalent in the elderly and patients with underlying chronic diseases, with established deleterious consequences such as the increased risk of respiratory infection. We reviewed the expected effects of zinc deficiency on COVID-19-related pathophysiological mechanisms focusing on both the renin-angiotensin and kinin-kallikrein systems. Mechanisms and effects were extrapolated from the available scientific literature. Zinc deficiency alters angiotensin-converting enzyme-2 (ACE2) function, leading to the accumulation of angiotensin II, des-Arg9-bradykinin and Lys-des-Arg9-bradykinin, which results in an exaggerated pro-inflammatory response, vasoconstriction and pro-thrombotic effects. Additionally, zinc deficiency blocks the activation of the plasma contact system, a protease cascade initiated by factor VII activation. Suggested mechanisms include the inhibition of Factor XII activation and limitation of high-molecular-weight kininogen, prekallikrein and Factor XII to bind to endothelial cells. The subsequent accumulation of Factor XII and deficiency in bradykinin are responsible for increased production of inflammatory mediators and marked hypercoagulability, as typically observed in COVID-19 patients. To conclude, zinc deficiency may affect both the renin-angiotensin and kinin-kallikrein systems, leading to the exaggerated inflammatory manifestations characteristic of severe COVID-19.