which decreased 1 h after a marathon, were
restored next morning to baseline levels in the
glutamine group, compared with the placebo
group (Castell et al.1997). In another of these
studies, white blood cells and neutrophils were
elevated after a marathon, but were closer to
baseline levels (P<0.05 and <0.001, respectively)
the next morning in the glutamine group com-
pared with the placebo group. For future studies,
it would be of interest to take samples at daily
intervals after a marathon in order to monitor
immune cell function, since the effect of a viral
attack should be manifest within 2–3 days of
running a marathon.
No increase in the plasma concentration of
glutamine was observed in samples from those
marathon runners who received glutamine
drinks after the race. However, for logistical
reasons, blood samples were not taken until
an hour after glutamine feeding, whereas the
peak concentration of plasma glutamine after a
bolus dose at rest occurred at 30 min (Castell &
Newsholme 1997). Glutamine supplementa-
tion in the doses used, and at the times ingested
after this series of marathon studies, appeared
to modify the incidence of URTI and to effect
two or three changes in concentrations of acute
phase response markers or in circulating cell
populations.
An important issue is whether measurements
of the numbers and activities of leucocytes in the
blood properly reflect the performance of the
immune system in the whole body. In human
studies, it is the only measurable link we have
with the much larger number of cells in the
whole immune system but the authors are
aware of the dangers of overinterpretation of
these data. The safety and efficacy of glutamine
feeding have been discussed by Ziegler et al.
(1990).There are now more than 120 published
reports on glutamine feeding studies: no prob-
lems of toxicity have been reported. It is
suggested that, in situations where plasma gluta-
mine levels in individuals are low, provision of
exogenous glutamine is a safe and simple
method of restoring physiological levels. This
might enhance the functional ability of cells of
166 nutrition and exercise
the immune system, as well as improving the
digestive and defence mechanisms of the intes-
tine, both for the patient and the athlete.Conclusion
In summary, the picture which emerges from
these studies is that infection levels are higher in
athletes undergoing exhaustive exercise of long
duration than in those undertaking shorter or
more moderate exercise. Glutamine concentra-
tion in the blood is decreased more by prolonged,
exhaustive exercise than by anaerobic/aerobic or
moderate exercise. More marked leucocytosis
and subsequent decrease in lymphocytes occurs
as a result of prolonged, exhaustive exercise
than anaerobic/aerobic or moderate exercise.
The decreases tend to occur at similar times and
within 3–4 h after prolonged, exhaustive exer-
cise: this creates an opportunity for apparent
immunosuppression to occur, which may coin-
cide with exposure to viral or bacterial agents.
The net result is an increase in the number of
infections, which appears to be modified by
glutamine feeding.
Much more work needs to be done, preferably
in well-controlled field studies, to obtain a more
accurate picture of precisely how glutamine
might be affecting the levels of infection per-
ceived in athletes after prolonged, exhaustive
exercise.Acknowledgements
The authors are indebted to the subjects for their
willing participation in the studies, and to Pro-
fessor Jacques Poortmans for his helpful com-
ments on this chapter.References
Altland, P.D. & Highman, B. (1961) Effects of exercise
on serum enzyme values and tissues of rats.
American Journal of Physiology 201 , 393–395.
Appell, H.J., Soares, J.M.C. & Duarte, J.A.R. (1992)
Exercise, muscle damage and fatigue.Sports Medicine
13 , 108–115.
Ardawi, M.S.M. & Newsholme, E.A. (1983) Glutamine