Should you take zinc for the common cold?
A new review suggests that taking zinc supplements can shorten the length of a cold. But many people who take zinc experience side effects, and we need more research to be sure it's worthwhile.
BMJ Group News
What do we know already?
The common cold is caused by a virus, which means it can't be treated with antibiotics. Often the best thing to do is rest, as colds usually go away on their own after a few days.
You can also take remedies from a pharmacy to help you feel better while your body fights off the cold. Painkillers may ease aches and pains, cold remedies may help clear a blocked nose or a cough, and there's a suggestion that certain vitamins and minerals, such as zinc, might help you recover from a cold faster.
But there hasn't been enough research to know if taking zinc improves the symptoms of a cold or makes a cold shorter, or if it could cause side effects.
Researchers reviewed all the evidence from studies where people were randomly assigned to take either zinc tablets or a dummy treatment (a placebo). They looked at 17 studies involving more than 2,000 people, and compared the two groups to see if people who took zinc recovered from their colds more quickly than people who took a placebo, or if their symptoms were more bearable.
What does the new study say?
People who took zinc had shorter colds than people who took a placebo. Taking zinc reduced the length of a cold by an average of just over a day and a half compared with taking a placebo.
People who took higher doses of zinc gained the most benefit. Taking the highest dose of zinc reduced the length of a cold by nearly three days compared with taking a placebo. Only one form of zinc supplement - zinc acetate - significantly reduced the length of colds. Other types of zinc supplement, including zinc gluconate and zinc sulphate, did not reduce the length of colds.
But the effect of zinc could only be seen in adults. When the researchers looked at adults and children separately, they found that taking zinc reduced the length of a cold by two and a half days in adults compared with taking a placebo. But there was no effect among children who took zinc.
Zinc did not have any effect on how severe people's cold symptoms were.
Taking zinc was also more likely to cause side effects than taking a placebo. The most common side effects were a bad taste in the mouth and nausea.
How reliable is the research?
There have been lots of small studies of zinc for the treatment of colds, and it can sometimes be difficult to know how reliable these small studies are, individually. Reviews like this, which pool the results of lots of studies - particularly studies that randomly assign people to zinc or a dummy treatment - are more reliable and provide a better source of evidence.
But there was a lot of variety between the different studies, and the researchers had to make some assumptions when doing their calculations to allow for this. This means we have to be cautious when making conclusions about the effect of zinc on colds.
What does this mean for me?
The researchers say that while their findings show that taking zinc supplements can shorten the length of a cold by around a day or two for adults, it's likely that the benefit may be outweighed by side effects, which were more common among people taking zinc than those taking a placebo.
Most colds do get better on their own, and you may find it more helpful to take painkillers, rest, and drink lots of fluids while your body recovers.