Taking a zinc supplement may cut how long respiratory infections last, while also easing symptoms, a review of limited evidence suggests.
The new study of 28 existing studies involving almost 5,500 people found that taking zinc by mouth or as a nasal spray could ward off infection and may make people feel better more quickly.
Respiratory tract infections (RTIs) can affect the sinuses, throat, airways or lungs, but most get better without treatment.
Symptoms of an RTI include cough, sneezing, stuffy or runny nose, sore throat, headache and a high temperature.
The new research, in the journal BMJ Open and from experts including from Western Sydney University, did not include data specifically related to Covid-19 cases.
It found that, compared with placebo, taking zinc could prevent five RTIs in 100 people per month, while on average symptoms resolved two days earlier if zinc was taken as a spray or under-the-tongue formula.
Overall, 19 more adults per 100 were likely to still have symptoms seven days into their illness if they had not taken zinc.
Meanwhile, there were “clinically significant” reductions in how people graded their symptoms three days into their illness.
The authors concluded: “In adult populations unlikely to be zinc deficient, there was some evidence suggesting zinc might prevent RTIs symptoms and shorten duration.
“The comparative efficacy/effectiveness of different zinc formulations and doses were unclear.”
Zinc is important for the immune system to function properly and is also vital for wound healing.
It is found in foods including oysters, crab, meat, chickpeas, mushrooms, spinach, broccoli, and kale.
The authors said more research was needed into zinc and pointed to the low-quality evidence in some of the studies.
Some people taking zinc in the research also said they felt sick or suffered mouth or nose irritation.
The most common zinc formulations used in the study were lozenges followed by nasal sprays and gels containing either zinc acetate or gluconate salts.
The researchers concluded that zinc is “a viable ‘natural’ alternative” for managing RTI symptoms at home, though they could not glean an ideal dose from the data.
“(Zinc) also provides clinicians with a management option for patients who are desperate for faster recovery times and might be seeking an unnecessary antibiotic prescription,” they added.
“However, clinicians and consumers need to be aware that considerable uncertainty remains regarding the clinical efficacy of different zinc formulations, doses and administration routes, and the extent to which efficacy might be influenced by the ever changing epidemiology of the viruses that cause (respiratory tract infections).”