Two strains of the SARS virus sequenced

EDITOR-Recently, the coronavirus was implicated as the cause of the
severe acute respiratory syndrome (SARS) (May 10, p 999) (1). In the
absence of a specific treatment for SARS, the possibility that vitamin C
may show nonspecific beneficial effects on respiratory infections should
be considered. The mechanisms whereby vitamin C affects the immune system
are not well understood, but there are numerous reports indicating that it
may affect the functions of phagocytes, the proliferation of T-
lymphocytes, the production of interferon, and the replication of viruses
(2). In particular, vitamin C has been shown to increase resistance of
chick embryo tracheal organ cultures to infection caused by the avian
coronavirus (3). Studies with animals have found that vitamin C modifies
susceptibility to various bacterial and viral infections (2). Murphy et
al. (4) inoculated marmosets with the parainfluenza virus, after which all
control animals (n=7) became infected in three days; only 7 animals in the
vitamin C group (n=14), however, became infected (P=0.03; Fisher's exact
test, 1-tail).

Studies on human subjects have reported decreased levels of vitamin C
in plasma, leukocytes, and in urine during various infections, including
pneumonia, which suggests that infections affect vitamin C metabolism (2).
Placebo-controlled trials have shown quite consistently that the duration
and severity of colds are reduced in the vitamin C group (2). Several
authors have suggested that vitamin C may hasten convalescence from
pneumonia (2), although I am aware of only one randomized trial pertinent
to this issue; it was carried out in the UK with elderly patients
suffering from pneumonia or bronchitis (5). Therapeutic vitamin C (0.2
g/day) caused a statistically significant decrease in a score of
respiratory symptoms in the patients who were most severely ill when
admitted to hospital, and a decrease bordering on statistical significance
in all patients (5). Furthermore, there were 6 deaths during the trial,
all due to respiratory infections: 5 of them in the placebo group (n=29),
but only 1 in the vitamin C group (n=28) (P=0.09; Fisher's exact test, 1-
tail). The possibility that therapeutic vitamin C supplementation may
reduce the severity of respiratory infections seems to warrant further
controlled trials, especially in the light of the SARS epidemic.

1 Dyer, O. Two strains of the SARS virus sequenced (news). BMJ
2003;326:999.

2 Hemilä H, Douglas RM. Vitamin C and acute respiratory infections.
Int J Tuberc Lung Dis 1999;3:756-61.

3 Atherton JG, Kratzing CC, Fisher A. The effect of ascorbic acid on
infection of chick-embryo ciliated tracheal organ cultures by coronavirus.
Arch Virol 1978;56:195-9.

4 Murphy BL, Krushak DH, Maynard JE, Bradley DW. Ascorbic acid and
its effects on parainfluenza type 3 virus infection in cotton-topped
marmosets. Lab Anim Sci 1974;24:229-32.

5 Hunt C, Chakravorty NK, Annan G, Habibzadeh N, Schorah CJ. The
clinical effects of vitamin C supplementation in elderly hospitalised
patients with acute respiratory infections. Int J Vitam Nutr Res
1994;64:212-19.

Competing interests:  
None declared