Will Zinc Prevent or Reduce a Cold?
Some studies have found a benefit to zinc-containing lozenges in reducing the duration of cold symptoms; other studies have not.
With the school year approaching, parents may wonder if they should start their children on zinc to prevent colds. Indeed, a few years ago a friend with school-aged kids asked me about using various zinc products to reduce the length of or prevent the common cold.
Years ago, I tried the nasal swab version of one of these products (Zicam) and was amazed at how painful they were. This prompted me to research the use of high concentrations of zinc as an immune-boosting supplement. What I found made me throw out the zinc swabs and never use a zinc-supplemented cold product again.
Zinc is a divalent positively, charged metal ion important for the function of various cellular proteins and cellular processes. All cells require this metal ion, which we get from food. However, too much zinc is toxic to cells. Ingestion or exposure to too much zinc causes zinc poisoning, which can require hospitalization. Because cells need just the right amount of zinc, cells have multiple mechanisms to control the concentration of intracellular zinc and the body eliminates excess zinc in urine. Systemic zinc poisoning arises when the body cannot eliminate this ion fast enough to prevent excess zinc from damaging cells.
In zinc-containing lozenges or nasal swabs, the amount of zinc is not high enough to cause systemic toxicity. However, the amount of zinc that the cells in contact with the swab could be enough to cause damage to those cells. Indeed, the Zicam nasal swab product has been discontinued because of the possibility of causing permanent damage to the cells in the nose that mediate smell.
Some studies have found a benefit to zinc-containing lozenges in reducing the duration of cold symptoms; other studies have not. The studies that showed effectiveness required using the lozenges every 2 hours while awake within 24 hours of onset of cold symptoms and side effects included nausea and bad taste. Ingredients other than zinc in the lozenges may alter their effectiveness in ways that have not been studied adequately. The 2013 study that reported a beneficial effect was retracted in 2016.
Zinc also interacts with other medicines and can have bad effects in people with other nutrient deficiencies. Thus, there isn’t strong evidence supporting the use of zinc supplements to prevent or treat colds. Depending on other health issues and medications, zinc supplementation can have unintended consequences.
Colds are caused by viruses. They cannot be treated with antibiotics. Some symptoms are caused directly by the virus in the infected cells, but most of the symptoms of a cold arise because of the body’s natural immune response to the infection. Even though the cells of the immune system need zinc, unless a person is deficient in zinc or eats less zinc than is needed for optimal cellular function, ingesting zinc or using a locally applied zinc product is unlikely to have a beneficial effect and could be harmful.
So what is the best way to treat a cold? The only real option is to take medicines that will reduce the symptoms of the immune response to the virus. Most cold medicines, not natural cold products, have 3 common ingredients: antihistamines, decongestants, and a nonsteroidal anti-inflammatory drug (NSAID). All of these drugs limit the immune response or reduce the symptoms arising from that response.
Antihistamines reduce the effect of histamine, a molecule released by mast cells of the immune system. Antihistamines reduce itchiness and sneezing, and block histamine from increasing the release of fluid from cells. Most antihistamines interact with the histamine receptor and with another class of receptors called the muscarinic acetylcholine receptor, which is why these often cause dry mouth and dry eyes. Antihistamines that cross the blood-brain barrier (like diphenhydramine, the active ingredient in Benadryl) also cause drowsiness. People with heart arrhythmias should consult their doctor before taking antihistamines because muscarinic acetylcholine receptors also control heart rate.
Decongestants act on receptors on arterial blood vessels and trigger constriction of the blood vessels, which reduces the amount of fluid that can move into the tissues from the circulation. Decongestants do not cross the blood-brain barrier. However, because they constrict arteries, these drugs can increase blood pressure and are typically contraindicated in people with high blood pressure.
NSAIDs (aspirin, ibuprofen, naproxen) reduce the production of prostaglandins and thereby reduce fever, swelling, and pain. NSAIDs reduce blood clotting and thus are not recommended for people taking any type of “blood thinner” or medication to reduce clotting. Cold medicines containing acetaminophen, instead of an NSAID, will be effective in reducing fever and discomfort, but will not reduce swelling of the nasal passages as NSAIDs will.
Although none of these types of medicines have zinc as an active ingredient, this trio of ingredients (antihistamine, decongestant, NSAID or acetaminophen) will help with the symptoms of a cold. Indeed, many cold medicines include combinations of these ingredients. They will not prevent an infected person from infecting others (other than by reducing the amount of sneezing and nasal secretions). They will not cure a cold, but they will bring symptomatic relief.
If you have reason to think your child is deficient in zinc or other nutrients, then you should talk with your pediatrician. Otherwise, eat a healthy diverse diet rich in plant-based foods, use proper hygiene, and deal with the occasional rhinovirus. Be sure to check the labels of medicines so that you don’t inadvertently take more than the recommended amount by taking multiple medicines together.
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Zinc poisoning, MedlinePlus. U. S. National Library of Medicine. https://medlineplus.gov/ency/article/002570.htm (accessed 5 August 2019)
Information on Zicam Cold Remedy Nasal Gel, Zicam Cold Remedy Nasal Swabs, and Zicam Cold Remedy Swabs, Kids Size. U. S. Food & Drug Administration. U. S. Department of Health and Human Services. https://wayback.archive-it.org/7993/20170111235859/http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm166834.htm (accessed 5 August 2019)
S. Marshall, Zinc gluconate and the common cold. Review of randomized controlled trials. Can. Fam. Physician. 44, 1037–1042 (1998). PubMed
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An earlier version of this article can be found at BioSerendipity:
N. R. Gough, Will zinc prevent or reduce a cold? BioSerendipity (13 September 2017) https://www.bioserendipity.com/2017/09/13/will-zinc-prevent-or-reduce-a-cold/.
Cite as: N. R. Gough Will zinc prevent or reduce a cold? Medium (5 August 2019).