7.3. Zinc Supplementation in Preventing Viral Infections
From the early 2000s, various studies were conducted, mainly in children from lower socio-economic settings, to establish whether daily or weekly zinc supplementation could help in preventing respiratory tract infections (Table 9) [269,270,271,272,273,274,275,276,277,278,279,280,281].
Different studies reported a reduced incidence of respiratory infections in the zinc receiving group [269,271,272,273,280]. In 2007, Sazawal et al. reported a slight reduction in the relative risk of all-cause mortality in children supplemented with zinc in Zanzibar [277]. Other studies found instead that zinc supplementation had no significant effect on the frequency of respiratory infections [274,275,276,278,279,281]. Some of these trials used a lower daily dose of zinc, which might be one of the reasons why the supplementation was less effective; however, both negative and positive results were reported with different zinc dosages, from 5 up to 30 mg/day.
Overall, different reviews and meta-analysis confirmed the efficacy of zinc supplementation in preventing respiratory illnesses: Aggarwal et al. reported that zinc supplementation for more than 3 months significantly reduced the frequency and severity of diarrhea and respiratory illnesses [282]; in 2010, Roth et al. found that routine zinc supplementation reduced the incidence of childhood ALRI [283]; in 2011, Yakoob and colleagues described a reduction in diarrhea and pneumonia mortality in children from developing countries who received zinc supplementation for over 3 months [284]; a 2016 systematic review also reported a statistically significant lower incidence of pneumonia (−13%) in children receiving zinc supplementation [285].