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NCCIH Clinical Digest

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The Common Cold and Complementary Health Approaches:
What the Science Says

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August 2017
A child sneezing into a handkerchief

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Clinical Guidelines, Scientific Literature, Info for Patients: 

Zinc

Oral zinc lozenges may reduce the duration of the common cold, when started within 24 hours and taken for a time period of less than 2 weeks. Intranasal zinc has been linked to a severe and permanent loss of smell and should not be used.

What Does the Research Show?

Several randomized controlled trials and systematic reviews and meta-analyses have been conducted to examine the effects of zinc for the common cold.

  • A 2015 meta-analysis of three randomized trials on zinc acetate lozenges for the common cold (dosages of 80-92 mg/day) found that zinc acetate lozenges shortened the duration of many common cold symptoms such as nasal discharge, nasal congestion, sneezing, sore throat, cough, and muscle ache. However, no differences in duration of headache and fever were seen. The authors concluded that zinc acetate lozenges (at doses of about 80 mg/day) may be a useful treatment for the common cold, started within 24 hours, for a time period of less than 2 weeks.
  • A 2013 review found that use of oral zinc reduces the duration of colds when taken within 24 hours of symptom onset and that prophylactic use of oral zinc reduces the incidence of cold, school and work absences, and antibiotic prescriptions. A 2012 systematic review and meta-analysis of 17 randomized controlled trials involving a total of 2,121 participants found similar results.
  • A 2012 review of the treatment of the common cold in pediatric patients concluded that evidence supports the use of oral zinc as a possible treatment and prevention of the common cold in children, although its use may be limited by the need for frequent administration and potential side effects, including bad taste, throat irritation, nausea, and diarrhea.

Safety

  • Oral zinc can cause nausea and other gastrointestinal symptoms.
  • Long-term use of zinc, especially in high doses, can cause copper deficiency and may increase the risk of urinary tract problems, reduce immune function, and cause other side effects.
  • Zinc may interact with drugs, including antibiotics and penicillamine.
  • The intranasal use of zinc can cause anosmia (i.e., loss of the sense of smell), which may be long-lasting or permanent. In 2009, the U.S. Food and Drug Administration warned consumers to stop using several intranasal zinc products marketed as cold remedies because they had been linked to cases of anosmia.

Vitamin C

For most people, vitamin C does not prevent colds and only slightly reduces their length and severity. Vitamin C is generally considered safe except when taken in high doses.

What Does the Research Show?

Several randomized controlled trials and a few reviews, including a Cochrane review, have examined the effects of vitamin C for treating or preventing the common cold.

  • A 2013 Cochrane review of results from 29 clinical trials involving more than 11,000 people found that taking vitamin C regularly (at least 0.2 grams per day) did not reduce the incidence of colds in the general population but may be useful for people exposed to brief periods of severe physical exercise (e.g., marathon runners, skiers, and soldiers training in subarctic conditions). Some studies have shown that vitamin C is associated with modest reductions in the length and severity of cold symptoms; however, these results were not replicated in the few therapeutic trials that have been conducted.
  • A 2012 review of treatment of the common cold in children and adults found that prophylactic vitamin C modestly reduces the duration of cold symptoms, but not the incidence of colds, in both children and adults.

Safety

  • Vitamin C is generally considered safe; however, high doses can cause digestive disturbances such as diarrhea, nausea, and abdominal cramps.

Echinacea

Although there is the potential that some preparations of echinacea are more effective than placebo for treating colds, the overall evidence for clinically relevant treatment effects is weak. Results of individual prophylaxis trials consistently show positive (though not significant) trends, although potential effects are of questionable clinical relevance.

Echinacea products vary widely, containing different echinacea species, plant parts, and preparations. The many clinical trials of echinacea for colds have also varied widely, in terms of products studied, research methods, and study results.

What Does the Research Show?

Several reviews, including a Cochrane review, of many randomized controlled trials mostly in adults have examined the effects of echinacea for preventing or treating colds.

  • A 2014 Cochrane review of 24 double-blind randomized controlled trials involving 4,631 participants concluded that echinacea products have not been shown to provide benefits for treating colds. Although there is the potential that some preparations are more effective than placebo for treating colds, the overall evidence for clinically relevant treatment effects is weak. This same review also concluded that the results of individual prophylaxis trials consistently show positive (though not significant) trends, although potential effects are of questionable clinical relevance.
  • A 2013 review concluded that therapeutic use of Echinacea purpurea may improve cold symptoms in adults, but the evidence is inconsistent. The review also concluded that prophylactic use of echinacea preparations is ineffective for preventing the common cold. The effects of echinacea in children are uncertain; only a small amount of research has been done in children, and the results of that research are inconsistent.

Safety

  • Few side effects have been reported in clinical trials of echinacea; however, some people may have allergic reactions.
  • In a 2003 randomized controlled trial conducted in children, use of Echinacea purpurea was associated with an increased risk of rash.

Probiotics

Currently, not enough research has been conducted to determine whether probiotics may prevent colds, and little is known about their long-term safety.

What Does the Research Show?

Several randomized controlled trials on a variety of strains and doses, as well as reviews and meta-analyses, have been conducted to examine the effects of probiotics on the common cold.

  • A 2015 Cochrane review of 13 randomized controlled trials involving 3,720 participants including children, adults, and older adults found that probiotics (any specified strain or dose) were better than placebo in reducing the number of participants experiencing episodes of acute upper respiratory tract infections (URTI), the mean duration of an episode of acute URTI, antibiotic use, and cold-related school absences. These findings suggest that probiotics may be more beneficial than placebo for preventing URTIs; however, the quality of the evidence was low or very low.
  • A 2014 systematic review and meta-analysis examined the effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infections and found evidence from “good-quality” randomized controlled trials that probiotics reduce the duration of illness in otherwise healthy children and adults.

Safety

  • As pointed out in a 2011 Agency for Healthcare Research and Quality assessment of the safety of probiotics, little is known about the long-term effects of probiotics.
  • It appears that most people can use probiotics without experiencing any side effects—or with only mild gastrointestinal side effects such as gas—but there have been some case reports of serious adverse effects, and the risk of serious side effects may be greater in people with underlying health conditions. Probiotics should not be used by people with serious underlying health problems except with close monitoring by a health care provider.

Saline Nasal Irrigation

Saline nasal irrigation may have benefits for relieving symptoms of the common cold in children and adults, and may have potential benefits for relieving some symptoms of acute upper respiratory infection.

What Does the Research Show?

Several randomized controlled trials in both children and adults, as well as a recent Cochrane review, have been conducted to examine the effects of saline nasal irrigation on the common cold.

  • A 2015 Cochrane review of five randomized controlled trials involving 544 children and 205 adults found that nasal saline irrigation possibly has benefits for relieving the symptoms of acute upper respiratory tract infections; however, the trials included in the review were generally too small and had a high risk of bias.
  • A 2012 review in children concluded that during acute illness, saline nasal irrigation can help alleviate sore throat, thin nasal secretions, and improve nasal breathing, and can reduce the need for nasal decongestants and mucolytics.

Safety

  • Nasal irrigation is generally safe; however, neti pots and other rinsing devices must be used and cleaned properly.
  • Most important is the source of water that is used with nasal rinsing devices. According to the U.S. Food and Drug Administration, tap water that is not filtered, treated, or processed in specific ways is not safe for use as a nasal rinse. Some tap water contains low levels of bacteria and protozoa, including amoebas, which can stay alive in nasal passages and cause potentially serious infections.
  • Improper use of neti pots may have caused two deaths in 2011 in Louisiana from a rare brain infection that the state health department linked to tap water contaminated with an amoeba called Naegleria fowleri.

Honey (Buckwheat)

Research suggests that buckwheat honey is superior to placebo for reducing frequency of cough, reducing cough, and improving quality of sleep for children with the common cold. Honey should not be used in children younger than 1 year of age because of the risk of botulism.

What Does the Research Show?

There have only been a couple of small studies in children that have examined the effects of honey for symptoms of the common cold.

  • A 2010 study, involving 139 children aged 2 to 5 years, compared the effect of honey, dextromethorphan, and diphenhydramine on nighttime cough and sleep quality and found that receiving a 2.5-mL dose of honey before sleep has a more alleviating effect on upper respiratory infection-induced cough compared with dextromethorphan and diphenhydramine doses.
  • A 2007 study of 105 children aged 2 to 18 with upper respiratory infections compared honey to similar pharmacologic agents and found that parents rated honey most favorably for symptomatic relief of their child’s nighttime cough and sleep difficulty due to upper respiratory tract infection.

Safety

  • Honey should not be used in children younger than 1 year of age because of the risk of botulism.

Geranium extract (Pelargonium sidoides)

Geranium extract (Pelargonium sidoides) may be helpful in relieving symptoms of acute bronchitis, acute sinusitis, and the common cold in children and adults, but the quality of evidence is low.

What Does the Research Show?

Several randomized controlled trials in adults and in children, and a recent Cochrane review, have been conducted to examine the effects of geranium extract on the common cold.

  • A 2013 Cochrane review of eight randomized controlled trials involving adults and children concluded that Pelargonium sidoides may be effective in relieving symptoms in acute bronchitis in adults and children, and sinusitis in adults. Also, Pelargonium sidoides may be effective in alleviating symptoms of acute rhinosinusitis and the common cold in adults, but there is some doubt. The overall quality of the evidence was considered low for main outcomes in acute bronchitis in children and adults, and very low for acute sinusitis and the common cold.
  • A 2007 double blind, randomized controlled trial in 103 adults with common colds found that Pelargonium sidoides (administered in liquid drops three times a day) significantly reduced the severity of symptoms and shortened the duration of the cold compared with placebo.

Safety

  • Research suggests that Pelargonium sidoides is generally well tolerated in most people.

Garlic

A recent Cochrane review concluded that there is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold.

What Does the Research Show?

Only a few clinical trials have been conducted to examine the effects of garlic supplements on the common cold.

  • A 2014 Cochrane review of a single randomized controlled trial, involving 146 participants who received either a garlic supplement or a placebo for 12 weeks, concluded that there is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. The single trial suggested that garlic may prevent occurrences of the common cold but more studies are needed to validate this finding.

Safety

  • Garlic is probably safe for most people in the amounts usually eaten in foods.
  • Taking garlic supplements may increase the risk of bleeding. Patients on anticoagulants should use caution before considering garlic supplements.
  • Garlic has been found to interfere with the effectiveness of some drugs, including saquinavir, a drug used to treat HIV infection.

References

  • Fashner J, Ericson K, Werner S. Treatment of the common cold in children and adults. Am Fam Physician. 2012;86(2):153–159.
  • Hao Q, Dong BR, Wu T. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. 2015;2:CD006895.
  • Hemilä H, Chalker E. The effectiveness of high dose zinc acetate lozenges on various common cold symptoms: a meta–analysis. BMC Fam Practice. 2015;16:24.
  • Karsch-Volk M, Barrett B, Kiefer D, et al. Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev. 2014;2:CD000530.
  • King D, Mitchell B, Williams CP, et al. Saline nasal irrigation for acute upper respiratory tract infections. Cochrane Database Syst Rev. 2015;4:CD006821.
  • King S, Glanville J, Sanders ME, et al. Effectiveness of probiotics on the duration of illness in healthy children and adults who develop common acute respiratory infectious conditions: a systematic review and meta-analysis. Br J Nutr. 2014;112(1):41–54.
  • Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database Syst Rev. 2014;11:CD006206.
  • Livingston C, Cozzens J, Hamilton A. FPIN’s clinical inquiries. Treatments for symptoms of the common cold. Am Fam Physician. 2013;88(12).
  • Lizogub VG, Riley DS, Heger M. Efficacy of a Pelargonium sidoides preparation in patients with the common cold: a randomized, double blind, placebo-controlled clinical trial. Explore (NY). 2007;3(6):573–584.
  • Paul IM, Beiler J, McMonagle A, et al. Effect of honey, dextromethorphan, and no treatment on nocturnal cough and sleep quality for coughing children and their parents. Arch Pediatr Adolesc Med. 2007;161(12):1140–1146.
  • Robohm C, Ruff C. Diagnosis and treatment of the common cold in pediatric patients. JAPPA. 2012;25(12):43–47.
  • Science M, Johnstone J, Roth DE, et al. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. CMAJ. 2012;184(10):E551–561.
  • Shadkam MN, Mozaffari-Khosravi H, Mozayan MR. A comparison of the effect of honey, dextromethorphan, and diphenhydramine on nightly cough and sleep quality in children and their parents. J Altern Complement Med. 2010;16(7):787–793.
  • Taylor JA, Weber W, Standish L, et al. Efficacy and safety of Echinacea in treating upper respiratory tract infections in children: a randomized controlled trial. JAMA. 2003;290(21):2824–2830.
  • Timmer A, Günther J, Motschall E, et al. Pelargonium sidoides extract for treating acute respiratory tract infections. Cochrane Database Syst Rev. 2013;10:CD006323.
  • U.S. Food and Drug Administration. “Is Rinsing Your Sinuses Safe?” Accessed at www.fda.gov/ForConsumers/ConsumerUpdates/ucm316375.htm on September 21, 2016.

NCCIH Clinical Digest is a service of the National Center for Complementary and Integrative Health, NIH, DHHS. NCCIH Clinical Digest, a monthly e-newsletter, offers evidence-based information on complementary health approaches, including scientific literature searches, summaries of NCCIH-funded research, fact sheets for patients, and more.

The National Center for Complementary and Integrative Health is dedicated to exploring complementary health products and practices in the context of rigorous science, training complementary health researchers, and disseminating authoritative information to the public and professionals. For additional information, call NCCIH's Clearinghouse toll-free at 1-888-644-6226, or visit the NCCIH Web site at nccih.nih.gov. NCCIH is 1 of 27 institutes and centers at the National Institutes of Health, the Federal focal point for medical research in the United States.

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This page last modified August 18, 2017