Pneumonia is an infection of the lungs usually caused by bacteria and viruses. Its clinical diagnosis is sometimes difficult. Pneumonia is more common in young children and in the aged. In low-income countries it causes two million deaths annually among young children. In the USA it is the most common cause of death from infection.
Vitamin C was identified in the early 1900s and suggestions that one of its biological roles may be to resist infections are supported by numerous animal studies. We looked for studies in humans and found three trials with a total of 2335 participants that looked at whether vitamin C prevents pneumonia in the community. Two of these preventive trials studied soldiers while the third studied boys in a UK boarding school in the 1940s. Two therapeutic trials with a total of 197 pneumonia patients looked at whether vitamin C might be beneficial for pneumonia patients. One studied patients aged 66 to 94 years in the UK with pneumonia. The other therapeutic trial was conducted in the former Soviet Union but the social and nutritional backgrounds of the patients were not described. One study with 37 burns patients examined the effect of vitamin C on hospital-acquired pneumonia. Our searches were up-date-as of April 2013.
Five of the identified trials found preventive or therapeutic benefits of vitamin C against pneumonia but the study on hospital-acquired pneumonia found no effect. The overall quality of the studies was good. However, the five trials with positive findings were carried out in such extraordinary conditions that the results should not be extrapolated to the general population. Therefore, more research is needed. In the meantime, supplementing pneumonia patients who have low plasma vitamin C levels may be reasonable because of its safety and low cost. None of the five trials reported noteworthy adverse effects of vitamin C.