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.

Probiotics and Disease: A Comprehensive Summary-Part 8, Gastrointestinal and Genitourinary Disorders.

This article series provides a literature review of the disease-specific probiotic strains associated with gastrointestinal and genitourinary disorders studied in published clinical trials in humans and animals. This is not an exhaustive review. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The goal of the probiotics and disease series is to provide clinically useful tools. The first article (part 1) focused on mental health and neurological conditions; the second article (part 2) explored cultured and fermented foods that are commonly available in the United States; the third article (part 3) explored the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society: cardiometabolic disease and fatigue syndromes; the fourth article (part 4) elucidated the role of the microbiome in infectious diseases; the fifth article (part 5) explored respiratory conditions of the ears, nose, and throat; and the sixth article (part 6) explored the relationship between beneficial microbiota and skin disorders. The seventh article (part 7) reviewed the relationship between beneficial microbiota and autoimmune diseases, allergies, asthma, and other immunity-related disorders. This article (part 8) will explore the unique relationship between bacterial strains and gastrointestinal and genitourinary diseases associated with dysbiosis. Future articles will review the influence of the microbiome on cancer development and prognosis, followed by an article focused on probiotic supplements. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 9, Cancer.

This article provides a literature review of the disease-specific probiotic strains associated with cancer. The literature review was restricted to research in both humans and animals. This is not an exhaustive review. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The goal of the probiotics and disease series is to provide clinically useful tools. The first article part 1 focused on mental health and neurological conditions; the second article part 2 explored cultured and fermented foods that are commonly available in the United States; part 3 explored the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society: cardiometabolic disease and fatigue syndromes; part 4 elucidated the role of the microbiome in infectious diseases; part 5 explored respiratory conditions of the ears, nose, and throat; part 6 explored the relationship between microbiota and skin disorders; part 7 reviewed allergy and autoimmune disease; and part 8 examined gastrointestinal and genitourinary conditions. This ninth article reviews the relationship between microbiota and cancer development and prognosis. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 3, Cardiometabolic Disease and Fatigue Syndromes.

This article series provides a literature review of the disease-specific probiotic strains, associated with cardiometabolic diseases and fatigue syndromes, studied in published clinical trials in humans and animals. This is not an exhaustive review. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The goal of the probiotics and disease series is to provide clinically useful tools. The first article (part 1) focused on mental health and neurological conditions and the second article (part 2) explored cultured and fermented foods that are commonly available in the United States. This third article (part 3) explores the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society: cardiometabolic disease and fatigue syndromes. Future articles will review conditions related to respiratory, ear, nose, and throat infections and infectious diseases; autoimmunity and dermatological conditions; cancer; and gastrointestinal and genitourinary, followed by an article focused on probiotic supplements. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 4, Infectious Diseases.

This article series provides a literature review of the disease-specific probiotic strains studied in published clinical trials in humans and animals. The goal of the series is to provide clinically useful tools. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The first article (part 1) focused on mental health and neurological conditions and the second article (part 2) explored cultured and fermented foods that are commonly available in the United States. The third article (part 3) explored the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society, cardiometabolic disease and fatigue syndromes. This fourth article (part 4) elucidates the role of the microbiome in infectious diseases. Future articles will review conditions related to infections of the upper respiratory system and ear, nose, and throat; autoimmunity and dermatological conditions; cancer; and gastrointestinal and genitourinary, followed by an article focused on probiotic supplements. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 5, Respiratory Conditions of the Ears, Nose, and Throat.

This article series provides a literature review of the disease-specific probiotic strains studied in published clinical trials in humans and animals. The goal of the series is to provide clinically useful tools. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The first article (part 1) focused on mental health and neurological conditions and the second article (part 2) explored cultured and fermented foods that are commonly available in the United States. The third article (part 3) explored the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society, cardiometabolic disease and fatigue syndromes. The fourth article (part 4) elucidated the role of the microbiome in infectious diseases, and this fifth article (part 5) investigates probiotic strains on respiratory conditions that affect the ears, nose, and throat. Future articles will review conditions related to autoimmunity and dermatological conditions; the influence of the microbiome on cancer development and prognosis; gastrointestinal and genitourinary diseases associated with dysbiosis conditions; followed by an article focused on probiotic supplements. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 6, Skin Health.

This article series provides a literature review of the disease-specific probiotic strains associated with dermatological disorders and conditions that have been studied in published clinical trials in humans and animals. This is not an exhaustive review. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The goal of the probiotics and disease series is to provide clinically useful tools. The first article (part 1) focused on mental health and neurological conditions, and the second article (part 2) explored cultured and fermented foods that are commonly available in the United States. The third article (part 3) explored the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society: cardiometabolic disease and fatigue syndromes. The fourth article (part 4) elucidated the role of the microbiome in infectious diseases, and the fifth article (part 5) examined respiratory conditions and conditions of the ears, nose, and throat. This sixth article (part 6) article explores the relationship between the microbiome and skin disorders. Future articles will review conditions related to autoimmunity and dermatological conditions; the influence of the microbiome on cancer development and prognosis, gastrointestinal and genitourinary diseases associated with dysbiosis conditions; followed by an article focused on probiotic supplements. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 7, Immune Disorders.

This article series provides a literature review of the disease-specific probiotic strains associated with immune and autoimmune conditions that have been studied in published clinical trials in humans and animals. This is not an exhaustive review. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The goal of the probiotics and disease series is to provide clinically useful tools. The first article (part 1) focused on mental health and neurological conditions, and the second article (part 2) explored cultured and fermented foods that are commonly available in the United States. The third article (part 3) explored the relationship between bacterial strains and 2 of the most prevalent diseases we have in modern society: cardiometabolic disease and fatigue syndromes. The fourth article (part 4) elucidated the role of the microbiome in infectious diseases, and the fifth article (part 5) examined respiratory conditions of the ears, nose, and throat. The sixth article (part 6) explored the relationship between beneficial microbiota and skin disorders. This seventh article (part 7) reviews the relationship between beneficial microbiota and autoimmune diseases, allergies, asthma, and other immunity-related disorders. Future articles will review the relationship between probiotics and skin disorders, the influence of the microbiome on cancer development and prognosis, and gastrointestinal and genitourinary diseases associated with dysbiosis, followed by an article focused on probiotic supplements. This literature review is specific to disease condition, probiotic classification, and individual strain.

Probiotics and Disease: A Comprehensive Summary-Part 1, Mental and Neurological Health.

This article series provides a literature review of the disease-specific probiotic strains studied in published clinical trials in humans and animals. The goal of the series is to provide clinically useful tools. The table designs allow for quick access to supportive data related to disease states and will be helpful as a guide for both researchers and clinicians. This first article (part 1) focuses on mental health and neurological conditions. Future articles in this series will review conditions related to cardiometabolic and fatigue syndromes; ear, nose, throat, respiratory, and infectious diseases; immune and dermatological conditions; cancer, gastrointestinal and genitourinary; followed by an article focused on food-based probiotic strains and nutritional supplements. This literature review is specific to condition, probiotic, and strain and also lists currently available products and foods in which these probiotics can be found. In part 1, we explore the role of probiotics in balancing mental health and neurological issues. Conditions in mental health include anxiety, depression, attention-deficit/hyperactivity disorder, and autism. Neurological conditions include age-related cognitive decline, hepatic encephalopathy, cerebral ischemia and reperfusion, traumatic brain injury, and multiple sclerosis.

Probiotics and Disease: A Comprehensive Summary-Part 2, Commercially Produced Cultured and Fermented Foods Commonly Available in the United States.

This article series provides a literature review of the disease-specific probiotic strains studied in published clinical trials in humans and animals. The goal of the series is to provide clinically useful tools. The table design allows for quick access to supportive data and will be helpful as a guide for both researchers and clinicians. The first article (part 1) focused on mental health and neurological conditions. This second article (part 2) explores cultured and fermented foods that are commonly available in the United States. Future articles will review conditions related to cardiometabolic and fatigue syndromes; ear, nose, throat, respiratory, and infectious diseases; immune and dermatological conditions; cancer; gastrointestinal and genitourinary; followed by an article focused on probiotic supplements. This literature review is specific to disease conditions, probiotic classification, and individual strains. In part 1, we explored foods, brands, bacterial strains, and the number of organisms at end of production (in colony-forming units). In part 2, we investigate many of the commercially available cultured and fermented probiotic rich foods that are currently available in the United States. This summary can serve as a quick reference guide for recommending probiotic rich foods to patients.