Acute lower respiratory infections, particularly pneumonia, are responsible for approximately one third of all childhood deaths in developing countries. Malnutrition increases both the severity and the incidence of these infections. Malnourished children have a decreased immunologic capacity, a problem attributable to zinc deficiency. Sazawal and colleagues conducted a double-blind, randomized trial to evaluate the effectiveness of zinc supplementation in improving immune status and reducing the incidence of lower respiratory infections in children.
Children enrolled in the study were between six and 35 months of age, were of low socioeconomic background and presented to a clinic in India for treatment of acute diarrhea. The children were assigned to receive either a 5-mL multivitamin preparation daily or 5 mL of zinc daily for six months. During episodes of acute diarrhea, children in the zinc group received 10 mL per day. Anthropometric assessments were conducted at baseline and at monthly intervals. Plasma zinc levels were measured at baseline and also after 120 days of supplementation. Zinc deficiency was defined as a plasma level less than 60 μg per dL (9.2 μmol per L). Information about the presence of fever, cough, difficulty in breathing and feeding was recorded every fifth day. Acute lower respiratory infection was defined as cough plus one or more of the following: tachypnea, temperature of 101°F (38.3°C) or lower chest wall retractions.
Of the 609 children enrolled in the study, 311 were assigned to the control group, and 298 were assigned to the zinc group. Plasma zinc levels were similar between the two groups at baseline. However, after 120 days of supplementation, zinc levels were significantly higher in the group receiving the zinc supplement. The number of episodes of acute lower respiratory infection was lower in the zinc group (0.19 episodes per child per year) when compared with the control group (0.35 episodes per child per year). In a corrected analysis using the World Health Organization's criteria for respiratory disease, zinc supplementation resulted in an 11 percent decrease in these infections. The reductions tended to be greater in children older than 11 months and in boys, but the differences were not statistically significant.
The authors conclude that zinc supplementation is effective in reducing the morbidity associated with acute lower respiratory infections in infants and children, possibly by improving immune status. Further research is needed to determine whether dietary supplements of zinc and other micronutrients, along with additional dietary modifications or fortification of staple foods, are a means of improving health in children.