With zinc sales climbing during the pandemic and in vitro studies showing the mineral fights respiratory viruses, including coronavirus, scientists from Australia published their results in the BMJ Open on zinc's ability to work against these viruses in vivo.
After a meta-analysis of 28 randomized controlled trials with more than 5000 participants included, researchers found that zinc reduces the severity of symptoms associated with respiratory viruses. Taken orally, sublingually, or intranasally, zinc was associated with a 28% lower risk of developing mild symptoms, a 32% lower risk of developing mild to moderate symptoms, and an 87% lower risk of developing moderately severe symptoms.
Zinc was also found to shorten symptom duration of respiratory infections. Compared with a placebo, groups administered zinc saw symptoms resolve 2 days earlier. Of note, groups that took zinc earlier on in the course of illness were more likely to recover sooner compared to controls.
Zinc has also been found to be effective against and is recommended by the World Health Organization for treating diarrhea in children. It works by regenerating the epithelium of the digestive tract and improving cell-mediated immunity. Zinc is also thought to be beneficial in slowing the progression of age-related macular degeneration.
Supplementation with zinc can include side effects of metallic taste, nausea, gastrointestinal discomfort, mouth irritation, loss of smell, and copper deficiency, although serious side effects such as permanent loss of smell from nasal sprays is considered rare. The tolerable upper intake level is 40 mg per day in adults.
The study's lead author Jennifer Hunter, PhD, BMed, states zinc's use in respiratory infections is mostly recommended for those who have reduced zinc absorption – people using PPIs, older adults, or those with chronic diseases that make it harder to ward off respiratory infections. In such cases, zinc is recommended at moderate doses in the long term or at relatively higher doses for short periods, such as 1 to 2 weeks.