A friend with kids who just went back to school 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 (Zn2+) is a 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 Zn2+ 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 Zn2+ (Figure 1), cells have multiple mechanisms to control the concentration of intracellular Zn2+. The body eliminates excess Zn2+ in urine. Systemic zinc poisoning arises when the body cannot eliminate this ion fast enough to prevent excess zinc from damaging cells.
On a local level, for example dissolvable zinc cold remedies or the 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 lozenge or dissolving tablet could be enough to cause damage to those cells. Indeed, I suspect that damage to the pain-sensing nerves is partially how the throat lozenges work. The Zicam nasal swab product has been discontinued because of permanent damage to the cells in the nose that mediate smell. My instinct for myself and my recommendation to my friends and family are to avoid any product touting zinc as the active ingredient especially if that product is intended to be given in such a way that it maintains contact with a particular part of the body for a prolonged period.
Colds are caused by viruses. They cannot be treated with antibiotics. Most of the symptoms of a cold arise because of the body’s natural immune response to the infection. The cells of the immune system need zinc, but there is no unequivocal evidence that exposing the nose or throat to a high concentration of zinc or taking zinc supplements will reduce the duration of a cold or make anyone less infectious. The 2013 study that reported a beneficial effect was retracted in 2016.
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 (Figure 2), 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. 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 of they constrict arteries, they 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. None of these have zinc as an active ingredient.
This trio of ingredients (antihistamine, decongestant, NSAID) will help with the symptoms of a cold. 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. 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.
Zinc poisoning, MedlinePlus. U. S. National Library of Medicine. https://medlineplus.gov/ency/article/002570.htm (accessed 13 September 2017)
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://www.fda.gov/Drugs/DrugSafety/ucm166834.htm (access 13 September 2017)
Das, R. R., Singh, M., Notice of Retraction: Das RR, Singh M. Oral Zinc for the Common Cold. JAMA. 2014;311(14):1440-1441. JAMA 316, 2678 (2016). PubMed
Cite as: 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/.