Sir,

Recently, a new coronavirus was identified as the cause of the severe acute respiratory syndrome (SARS).1 In the absence of a specific treatment for SARS, the possibility that vitamin C may show non-specific effects on severe viral respiratory tract infections should be considered. There are numerous reports indicating that vitamin C may affect the immune system,2,3 for example the function of phagocytes, transformation of T lymphocytes and production of interferon. In particular, vitamin C increased the resistance of chick embryo tracheal organ cultures to infection caused by an avian coronavirus.4 Studies in animals found that vitamin C modifies susceptibility to various bacterial and viral infections,3 for example protecting broiler chicks against an avian coronavirus.5 Placebo-controlled trials have shown quite consistently that the duration and severity of common cold episodes are reduced in the vitamin C groups,3 indicating that viral respiratory infections in humans are affected by vitamin C levels. There is also evidence indicating that vitamin C may affect pneumonia.3 In particular, three controlled trials with human subjects reported a significantly lower incidence of pneumonia in vitamin C-supplemented groups,6 suggesting that vitamin C may affect susceptibility to lower respiratory tract infections under certain conditions. The possibility that vitamin C affects severe viral respiratory tract infections would seem to warrant further study, especially in light of the recent SARS epidemic.

*

Tel: +359-0-191-27573; Fax: +358-0-191-27570; E-mail: harri.hemila@helsinki.fi

References

1.

Holmes, K. V. (

2003
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2.

Leibovitz, B. & Siegel, B. V. (

1981
). Ascorbic acid and the immune response.
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135
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1
–25.

3.

Hemilä, H. & Douglas, R. M. (

1999
). Vitamin C and acute respiratory infections.
International Journal of Tuberculosis and Lung Diseases
3
,
756
–61.

4.

Atherton, J. G., Kratzing, C. C. & Fisher, A. (

1978
). The effect of ascorbic acid on infection of chick-embryo ciliated tracheal organ cultures by coronavirus.
Archives of Virology
56
,
195
–9.

5.

Davelaar, F. G. & Bos, J. (

1992
). Ascorbic acid and infectious bronchitis infections in broilers.
Avian Pathology
21
,
581
–9.

6.

Hemilä, H. (

1997
). Vitamin C intake and susceptibility to pneumonia.
Pediatric Infectious Diseases Journal
16
,
836
–7.