A Cochrane review [Abstract] 1 included 10 studies with a total of 33 979 subjects. Most studies found no significant effect of vitamin A on the incidence of acute lower respiratory tract infection (LRTI), or prevalence of symptoms of acute LRTI. Vitamin A caused an increased incidence of acute LRTI in one study; an increase in cough and fever; and increased symptoms of cough and rapid breathing in two others. Three reported no differences and no protective effect of vitamin A. Two studies reported that vitamin A significantly reduced the incidence of acute LRTI with children with poor nutritional status or weight, but increased it in normal children.
Comment: The quality of evidence is downgraded by inconsistency (variability in results across studies and heterogeneity in interventions and outcomes).
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