It’s been a few months since I blogged about hydroxychloroquine and COVID-19, and I’m still getting emails defending its use, even as more and more evidence has emerged to show that it is not effective to prevent or treat the disease, regardless of setting. It seems, according to some disgruntled readers, that I didn’t properly account for the magical healing powers of zinc in my analysis. I regularly receive apparent statements of fact like “The hydroxychloroquine helps zinc to enter cells and stop the virus,” backed not by references, but by ALL CAPS telling me just how ignorant I am to even write about the topic. So today’s post is a closer look at zinc.
Zinc as an antiviral is nothing new. It’s one of the first “alternative” medicines I remember researching way back in the 1990s, when claims circulated that zinc lozenges could shorten the duration of a cold. And the studies into zinc lozenges go way back into the 1980s. Working often in community pharmacy settings, there were regular requests for zinc lozenges during cold and flu seasons, usually followed by complaints from consumers about their (lack of) palatability. It’s been a topic of this blog over the years, most notably when a “homeopathic” zinc spray was identified that (1) actually contained zinc and (2) caused a loss of the ability to smell.
Do we need zinc at all?
In short, yes. Zinc is a trace mineral with functions throughout the body. Zinc deficiency is a significant issue worldwide where access to a healthy diet and adequate calories is a problem. In diets where foods that contain zinc (e.g., meat, shellfish, chicken, nuts, lentils) are consumed regularly, zinc deficiency is less common, but still possible. Depending on where you live, some foods may be fortified with zinc, such as breakfast cereals. Severe deficiencies when food access is not a problem are more common where there are chronic diseases that cause reduced absorption (e.g., inflammatory bowel diseases) or as a consequence of gastrointestinal tract surgery. Some medications can increase the body’s loss of zinc as well (e.g., diuretics).
A severe zinc deficiency is most commonly associated with impaired growth, but the effects include immune system dysfunction. So being deficient in zinc could conceivably affect your susceptibility or response to a COVID-19 infection, but there is no evidence to suggest that supplementing with zinc has any meaningful effects. Absence of evidence is not evidence of absence, and the signals of benefit that have appeared in research studying zinc supplementation and the common cold (which can be caused by coronaviruses, among other viruses) has led to questions about whether or not zinc is a reasonable preventative option to try, considering overall risks and benefits.
The evidence for zinc to prevent or treat the common cold
There is no evidence to suggest that zinc-containing nasal sprays are safe or effective and they should be avoided. The same can be said for anything labelled as “homeopathic”. The preparations that have been the most studied are lozenges and tablets. One systematic review, published in 2011, identified 13 placebo-controlled trials with wide variation in doses. Low doses (<75mg/day) were found to be ineffective and trials with higher doses were founds to reduce the duration of colds (by 42%), but not their incidence. Another systematic review included 17 trials that compared zinc to placebo or no treatment. This analysis found that zinc reduced the duration of cold symptoms (by an average of 1.65 days) but the results varied widely across the trials. This review noted that adverse events (taste, nausea) were more common in the zinc group. Finally a Cochrane review from 2013 was withdrawn in 2015, citing concerns with the data analysis. It remains withdrawn as of the last update in 2016.
So should you take zinc to prevent or treat COVID-19?
Malnutrition in general is associated with reduced immunity, so situations where zinc deficiency is known, or highly likely, should be addressed, just as they should be for other vitamin deficiencies. There is some evidence that lower zinc levels may be associated with poorer outcomes from COVID-19 infections. Whether it’s the zinc, or zinc is just a surrogate for another factor, is not established.
Supplementing with zinc, in the absence of a known deficiency, is trickier. One approach for those interested in minimizing any risk, even theoretical, could include looking at your diet and then evaluating whether it is providing you with adequate zinc. For most of you without major medical conditions or restrictive diets, it probably is. Regular supplementation in the absence of a deficiency has some risks, however, as long-term high doses can interfere with copper absorption. Moreover, zinc is not easy to take as a supplement, especially in lozenge form, and can cause nausea and stomach upset. If you are feeling sick and decide to start supplementing with zinc lozenges, there is no persuasive evidence to suggest that it will be harmful, but neither is there good evidence to suggest it will offer you much benefit. And if in spite of the lack of evidence, you want to take a zinc supplement routinely, it will likely be safe as long as you keep the daily dose low (stay under 40mg/day, if you’re an adult). Just keep distancing, masking, and avoiding crowded indoor spaces.