Vitamin C for preventing and treating pneumonia

Hemilä H, Louhiala P

Published Online:

July 6, 2011

Pneumonia is an infection of the lungs caused by bacteria, viruses or other infectious agents. 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. Two of the preventive trials studied soldiers while the third studied boys in a UK boarding school in the 1940s. Two other trials with a total of 197 pneumonia patients looked at whether vitamin C might help to cure pneumonia. One studied patients aged 66 to 94 years in the UK with pneumonia and benefit was restricted to those who were most ill and had low vitamin C levels. The other trial was conducted in the former Soviet Union but the social and nutritional backgrounds of the patients were not described. None of the five trials reported noteworthy adverse effects of vitamin C.

Overall, the results of the five identified trials suggested vitamin C is beneficial in both preventing and treating pneumonia. However, these trials were carried out in such extraordinary conditions that the results may not apply 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.

Abstract (click to read)

Background:

Pneumonia is one of the most common, serious infections, causing two million deaths annually among young children in low-income countries. In high-income countries pneumonia is most significantly a problem of the elderly.

Objectives:

To assess the prophylactic and therapeutic effects of vitamin C on pneumonia.

Search strategy:

We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2011, Issue 1) which contains the Acute Respiratory Infections Group’s Specialised Register, MEDLINE (1950 to January week 4, 2011), EMBASE (1974 to February 2011) and Web of Science (1945 to February 2011).

Selection criteria:

To assess the therapeutic effects of vitamin C, we selected placebo-controlled trials. To assess prophylactic effects, we selected controlled trials with or without a placebo.

Data collection and analysis:

Two review authors independently read the trial reports and extracted data.

Main results:

We identified three prophylactic trials which recorded 37 cases of pneumonia in 2335 people. Only one was satisfactorily randomised, double-blind and placebo-controlled. Two trials examined military recruits and the third studied boys from "lower wage-earning classes" attending a boarding school in the UK during World War II. Each of these trials found a statistically significant (80% or greater) reduction in pneumonia incidence in the vitamin C group. We identified two therapeutic trials involving 197 pneumonia patients. Only one was satisfactorily randomised, double-blind and placebo-controlled. That trial studied elderly patients in the UK and 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 trial studied adults with a wide age range in the former Soviet Union and found a dose-dependent reduction in the time to recovery with two vitamin C doses.

Authors' conclusions:

The prophylactic use of vitamin C to prevent pneumonia should be further investigated in populations who have high incidence of pneumonia, especially if dietary vitamin C intake is low. Similarly, the therapeutic effects of vitamin C should be studied, especially in patients with low plasma vitamin C levels. The current evidence is too weak to advocate widespread prophylactic use of vitamin C to prevent pneumonia in the general population. However, therapeutic vitamin C supplementation may be reasonable for pneumonia patients who have low vitamin C plasma levels because its cost and risks are low.

This record should be cited as:

Hemilä H, Louhiala P. Vitamin C for preventing and treating pneumonia. Cochrane Database of Systematic Reviews 2007, Issue 1. Art. No.: CD005532. DOI: 10.1002/14651858.CD005532.pub2

Assessed as up to date:

April 19, 2011

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Primary Review Group:

Acute Respiratory Infections Group

PEARLS - Practical Evidence About Real Life Situations (click to read)

Clinical question:

Does vitamin C have a prophylactic or therapeutic effect in patients with/ at risk of pneumonia?

Bottom line:

There is no evidence to support widespread prophylactic use of vitamin C to prevent pneumonia in the general population. However, therapeutic vitamin C supplementation may be reasonable for pneumonia patients who have low plasma vitamin C levels because its costs and risks are low.

Caveat:

Several of the studies reviewed date from many years ago and were conducted in such extraordinary conditions e.g extreme cold that the results may not apply to the general population. There were 37 cases of pneumonia out of 2335 participants.

Context:

Pneumonia is relatively common, particularly in young children and the aged. It is the most common cause of admission to hospital for adults in some developed countries

Cochrane Systematic Review:

Hemilia H et al. Vitamin C for preventing and treating pneumonia. Cochrane Reviews, 2007, Issue 1. This review had 5 trials which contributed data to the review. The studies ranged from 226 to 1435 participants.

Authored by:

Brian R McAvoy

Cochrane Primary Health Care Field

Health topics:

Infectious disease > Respiratory infections > Pneumonia

Lungs & airways > Respiratory infections > Pneumonia

Complementary & alternative medicine > Infectious disease > Respiratory infections

Complementary & alternative medicine > Lungs & airways > Respiratory infections

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Vitamin C for preventing and treating pneumonia

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