In fact, taking zinc lozenges at the first signs of a cold may actually lengthen the number of days that symptoms persist, the study reports.
The study’s Finnish authors stress, however, that these findings shouldn’t be construed as the final word on whether zinc lozenges are effective against the common cold — even if they do come from a randomized controlled clinical trial (considered the gold standard of medical research).
“Our study does not confirm the usefulness of zinc lozenges for treating the common cold, but neither does it refute the previous studies where zinc lozenges were found to be effective,” says Dr. Harri Hemila of the University of Helsinki, in a released statement.
Under different conditions than those in the study — at higher doses, for example — zinc lozenges may shorten the length of a cold, he points out.
Still, the study underscores how little we really know about zinc and other popular “remedies” for illnesses like the common cold — and why we should be exceedingly cautious before using them (to protect our health as well as our pocketbooks).
As Hemila and his co-authors explain in their paper, previous research on zinc’s usefulness in treating the common cold has had conflicting results. Eight studies found zinc lozenges to be beneficial in fighting off cold symptoms, while 12 others did not.
Those differences might be due to variations in the types of the lozenges used in the studies. The researchers note that certain substances, such as citric acid, bind strongly to zinc ions, hampering the mineral’s ability to be released in the body.
For the current study, the Finnish researchers used zinc acetate lozenges. Acetate binds to zinc ions very weakly. The researchers also prescribed the zinc in daily doses of 78 milligrams, which is the amount that several previous studies with positive findings had used.
The study was conducted from Dec. 1, 2017, through April 30, 2018. Its 253 participants were employees of the city of Helsinki. All were aged 18 or older, and all said they usually had at least one cold per winter.
A package of lozenges was mailed to the participants at the start of the study. Half received zinc acetate lozenges. The others received placebo lozenges. Neither the participants nor the researchers knew which lozenges they had been given.
The participants were instructed to report back to the researchers at the first signs of a cold. They were then to immediately start taking the lozenges by dissolving six per day in their mouth and then to continue that dosage schedule for five days. During each day they were ill, the participants also filled out online questionnaires regarding their symptoms, which, of course, included sneezing, coughing, sore throat, nasal congestion, aching muscles and headache.
Eighty-eight of the participants ended up catching a cold during the study: 46 in the zinc group and 42 in the placebo group. (A woman in the zinc group had to drop out of the study after one day, however, due to a severe reaction to the zinc.)
The study found no difference between the zinc and placebo groups in how quickly they recovered from their sneezing, coughing and other symptoms during the five days of treatment. Unexpectedly, however, people in the zinc group were more likely than those in the placebo group to have their symptoms linger for another two days.
In other words, their colds tended to last longer. The researchers say that finding needs to be confirmed or refuted in future studies.
Twice as many people in the zinc group than in the placebo group (63 percent versus 31 percent) reported side effects from the lozenges. The zinc users most commonly complained about the lozenges tasting terrible, although the taste was not bad enough, apparently, to reduce their average use of the lozenges compared to the placebo group.
Limitations and implications
The study comes with caveats. Most notably, the participants self-reported their cold symptoms. Those reports may not have accurately reflected when the symptoms started and finished. Also, the participants were not asked to return their lozenge packages, so there was no objective way of knowing whether they complied with the instructions and actually took all the pills prescribed.
Still, this was a well-designed study. At a minimum, it suggests that zinc lozenges should not be recommended for treating the common cold until more research is done.
“We found that common cold symptoms were not shortened by a commercially available zinc acetate lozenges with an instruction of 78mg/day for 5 days,” the researchers conclude.
“In future trials of the benefits and harms of commercially available zinc lozenges for common cold treatment, the lozenges should be more slowly dissolving in mouth, the dose should be over 92mg/day and the treatment should last longer than 5 days,” they add.
Of course, there’s no guarantee that even then the lozenges would work. Stay tuned.
FMI: You can read the study in full on the BMJ Open website.