et al. 1990), a vitamin C restricted diet was fol-
lowed by reduced whole blood ascorbic acid con-
centration. The marginal vitamin C supply did
not produce any significant effects on maximal
aerobic capacity or lactate threshold in healthy
volunteers. Carnitine, or any other metabolites
related to vitamin C status, was not measured.
Vitamin C supplementation has been associ-
ated with increased maximal aerobic capacity
(Buzinaet al. 1982; Suboticanec-Buzina et al. 1984)
and work efficiency (Powers et al. 1985) in mal-
nourished children. However, the above positive
effects were seen simultaneously with supple-
mentation of one or more vitamins of the B-
complex group. Hence, the independent role of
ascorbic acid was not shown. The majority of
other studies have not shown any measurable
effects of vitamin C supplementation on maxi-
mal oxygen uptake, lactate threshold or exercise-
induced heart-rate in well-nourished subjects
(Gerster 1989).
Due to its function as an antioxidant in phago-
cytic leucocytes, supplementary vitamin C may
slightly decrease the duration of common cold
episodes (Hemilä 1992). The study of Peters et al.
(1993) provided evidence that 600 mg vitamin C
daily reduced the incidence (33% vs. 68%) and
duration (4.2 vs. 5.6 days) of upper-respiratory-
tract infection in runners after a 90-km ultra-
marathon race. It is not known, however,
whether the potential effect of vitamin C supple-
mentation on the common cold in athletes has
any significant long-term effects on performance.
In a large epidemiological survey in the US,
dietary vitamin C intake was weakly but
positively associated with pulmonary function
(forced expiratory volume in 1 s) in healthy sub-
jects, but a stronger relationship was found in
asthmatic patients (Schwartz & Weiss 1994). The
authors postulated that the antioxidant effects of
vitamin C have a protective role on pulmonary
function. Finally, earlier results suggest that
vitamin C supplementation (≥250 mg daily)
might reduce heat strain in unacclimatized indi-
viduals (Kotze et al. 1977) which could theoreti-
cally enhance physical performance in certain
circumstances.
safety of elevated
vitamin c intake
There are reports suggesting that very high (>1g
daily), chronic doses of vitamin C might lead to
formation of oxalate stones, increased uric acid
excretion, diarrhoea, vitamin B 12 destruction and
iron overload, and induce a dependency state
(Alhadeff et al. 1984). However, excluding diar-
rhoea, the risk for the above toxic effects is likely
to be very low in healthy individuals, even with
intake of several grams daily (Marks 1989; Rivers
1989).Fat-soluble vitamins
Vitamin Echemistry and
biochemical functions
Vitamin E consists of a trimethylhydroquinone
head and a diterpenoid side chain (Jenkins 1993).
The most active biological form of vitamin E is a-
tocopherol. It is stored in many tissues, with the
largest amount in the liver. Vitamin E is trans-
ported mainly in very low density lipoproteins.
Vitamin E is one of the most important antioxi-
dants in cellular membranes (see Chapter 22),
and it stabilizes the structural integrity of mem-
branes by breaking the chain reaction of lipid
peroxidation (Jenkins 1993). Vitamin E is also
essential for normal function of the immune
system (Meydani 1995).supply and metabolic functions
It has been hypothesized that free radical
damage to mitochondrial membranes in vitamin
E depletion would impair the reactions of oxida-
tive phosphorylation, and hence physical work
capacity. Vitamin E deficiency is, however, very
rare, and the relationship between decreased
vitamin E supply and physical capacity has not
been investigated (Jenkins 1993).
Supplementation of vitamin E has well-
established and rather consistent effects on some