No proof yet that zinc lozenges will ‘knock days off your cold’

    19 July 2016

    Zinc lozenges can reduce the time it takes to recover from the common cold from seven days to four, research at the University of Helsinki has claimed.

    The study, published in the British Journal of Clinical Pharmacology, reviewed previous clinical trials in which patients consumed at least 75mg of zinc daily.

    The 199 participants, who were mostly female and between the ages of 20 and 50, were given a zinc lozenge every two to three hours. The researchers found that those who took the lozenges no longer had cold symptoms after an average of four days, whereas those on a placebo pill were still ill after seven days.

    The benefits of zinc were not altered by other factors such as allergies, age or sex.

    Dr Harri Hemila, the study’s lead author, said: ‘Ordinary tablets that enter directly into the stomach, without releasing zinc in the pharyngeal [throat] region, are not effective.’

    He also advised against taking lozenges with citric acid in them, saying these can prevent the release of zinc into the body.

    ‘Common cold patients should try zinc lozenges with doses of about 80 to 100mg per day very soon after the onset of the common cold,’ he said.

    Interest in the effect of zinc on colds began in the 1980s, when a three-year-old girl suffering from leukaemia was given zinc tablets and, struggling to swallow them, dissolved them in her mouth instead. This seemed to shorten the duration of her colds.

    Instant analysis
    This study aggregates three randomised controlled trials, each of which is very small. The total number of patients is only 199. I do not, therefore, think the conclusions are very robust.

    The people involved in this area of research are very keen to prove their hypothesis, which makes me more sceptical. The references in the study repeat the same small group of names.

    The paper notes that previous studies into the effect of zinc on colds have had variable results, but puts this entirely down to variable dosing and formulation.

    The author has had a long-running disagreement with the authors of a Cochrane Collaboration meta-analysis. That review has now been retracted. (The authors of the review have defended their approach here.) Up until present, no new guidance has been published, but question marks remain about data quality, standardisation and selective reporting in the studies and analysis. 

    From a practical point of view the zinc lozenges seem like quite a faff. You have to take high-dose lozenges every one and a half hours for the first day and every two hours on following days. The lozenges have to be dissolved in your mouth — they cannot be swallowed. And they taste awful.

    I hope some independent research arrives soon to clarify the subject, as the water looks muddy from where I stand. 
    Research score: 1/5