A Cochrane review [Abstract] 1 included 3 prophylactic trials with a total of 2 335 subjects, recording 37 cases of community-acquired pneumonia, 2 therapeutic trials involving 197 community-acquired pneumonia patients, and one prophylactic trial recording 13 cases of hospital-acquired pneumonia in 37 patients. Only one prophylactic and one therapeutic trial on community-acquired pneumonia was satisfactorily randomised, double-blind and placebo-controlled. Prophylactic studies: Two studies examined military recruits, and one studied boys from "lower wage-earning classes" attending a boarding school in the UK during World War II. All these prophylactic trials found a statistically significant (80% or greater) reduction in pneumonia incidence in the vitamin C group. One prophylactic study included 37 severely burned hospitalized patients; one-day administration of vitamin C had no effect on pneumonia incidence. Therapeutic studies: A therapeutic study among elderly patients in the UK found lower mortality and reduced respiratory symptom scores in the vitamin C group; however, the benefit was restricted to the most ill patients. The other therapeutic study among adults (with a wide age range) in the former Soviet Union found a dose-dependent reduction in the time to recovery with two vitamin C doses.
Comment: The quality of evidence is downgraded by limitations in study quality and by imprecise results (limited study size for each comparison).
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