found that taking zinc may prevent five RTIs in 100 people per month, and on average, symptoms resolved two days earlier if zinc was taken through an under-the-tongue method or as a spray.
In the group that did not take zinc, it was found that 19 more adults per 100 were still likely to have RTI symptoms seven days into their illness.
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, found in foods like meat, mushrooms, chickpeas, spinach, broccoli, kale, oysters and crab, is important for wound healing as it helps the immune system to function properly.
Some participants did mention feeling sick or suffered from mouth or nose irritation.
The authors said more research was needed into zinc, as there was some low-quality research in some of the studies.
In the study, the most common zinc formulas were lozenges, followed by nasal sprays and gels containing either zinc acetate or gluconate salts.
The researchers said zinc is "a viable 'natural' alternative" to manage RTI symptoms at home, although an ideal dose was not mentioned.
“(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).”