Since 1984, researchers have debated whether zinc helps people to fight off colds. In that time, five studies have found that it helps, while five others established no such benefit.
A report in the Aug. 15 Annals of Internal Medicine now tilts the balance in favor of zinc, finding that lozenges taken every few hours at the start of a cold slash its average duration nearly in half.
Researchers gave 25 people zinc acetate dihydrate lozenges within 24 hours of the onset of a cold; 23 others received an inert substitute. Both lozenges tasted of peppermint. Neither researchers nor participants were told who was receiving zinc until afterward. Participants took a lozenge every 2 to 3 hours for 4 or 5 days.
People getting 80 milligrams of zinc a day reported their overall cold symptoms abated in less than 5 days, compared with 8 days on average for the group getting placebos, says study coauthor Pranatharthl H. Chandrasekar, a physician at Wayne State University School of Medicine in Detroit. In particular, participants getting zinc reported significantly less coughing and nasal discharge than the people receiving the placebo did.
In one of the earlier studies, people taking zinc complained of nausea and diarrhea. Those problems didn’t turn up in this trial, but zinc did cause some constipation and mouth dryness.
Some doubt lingers as to whether these people were truly in the dark about whether they were getting zinc. “It has a very disagreeable taste that’s hard to mimic with a placebo,” Chandrasekar says. Thus, the belief that they were getting the real medicine might have influenced how the zinc recipients assessed their recovery, he says.
Although the mechanism by which zinc might fight cold symptoms isn’t known, Chandrasekar suspects that the element represses the formation of cytokines. These proteins gush forth from immune cells in response to the cold virus and spawn.