61 1
ClinicalScience (1991)80,611-618
Increased blood antioxidant systems of runners in response to
training load
J. D. ROBERTSON, R. J. MAUGHAN*, G. G. DUTHIE
AND
P. C. MORRICE
The Rowett Research Institute, Bucksburn, Aberdeen and *University Medical School, Foresterhill, Aberdeen, U.K.
(Received 23 November 1990; accepted 14 January 1991)
SUMMARY
1. Blood antioxidants were measured in venous blood
samples from 20 runners and six sedentary individuals.
All subjects were male, between 20 and 40 years old, and
in steady state with respect to body weight and physical
activity patterns. Dietary analysis was undertaken using a
7-day weighed food intake. Correlations were sought
between antioxidants in blood and (1)weekly training
distance and (2)maximum oxygen uptake. In addition, 12
runners could be classified into two groups undertaking
either low (range 16-43 km, n = 6 ) or high (80-147 km,
n = 6) weekly training.
2. Body weight (range 55.3-90.0 kg) and percentage
body fat (range 7-19%) both showed negative correlations with the weekly training distance (both P< 0.001).
Energy intake and maximum oxygen uptake were both
correlated with the weekly training distance (both
P<O.OOl).
3. Plasma creatine kinase activity, an indicator of
muscle damage, was si@cantly correlated with the
weekly training distance (P<0.01), whereas the plasma
concentration of thiobarbituric acid-reactive substances,
an indicator of free-radical-mediated lipid peroxidation,
decreased with increased maximum oxygen uptake
( P< 0.01).
4. Erythrocyte a-tocopherol content was greater in
the two running groups (P<0.05) compared with the
sedentary group, and lymphocyte ascorbic acid concentration was significantly elevated in the high-training
group (P<0.0 1)compared with the low-training group.
5. Erythrocyte activities of the antioxidant enzymes,
glutathione peroxidase and catalase, were significantly
and positively correlated with the weekly training distance
(P<0.01 and P < 0.05, respectively). Total erythrocyte
glutathione content was higher in the two training groups,
and was accounted for by an increase in reduced glutathione content.
Correspondence: Dr J. D. Robertson, Department of Environmental and Occupational Medicine, University Medical
School, Aberdeen AB9 2ZD, U.K.
6. These results indicate that there is an increase in
blood antioxidant defence mechanisms associated with
endurance training or the related l i e style, but despite this
there is a degree of muscle damage in the training
individuals.
Key words: antioxidants, exertion, vitamins.
Abbreviations: CAT, catalase (EC 1.11.1.6); CK, creatine
kinase (EC 2.7.3.2); GSH, reduced glutathione; GSHPx,
glutathione peroxidase (EC 1.11.1.9); GSSG, oxidized
glutathione; SOD, superoxide dismutase (EC 1.15.1.1);
TBARS, thiobarbituric acid-reactive substances;
Vo2max.,maximum oxygen uptake.
INTRODUCTION
Oxygen utilization may increase tenfold during endurance
exercise in association with an increase in the mitochondrial generation, or the metabolic 'leak', of superoxide and hydrogen peroxide [l-41. Therefore prolonged
physical exercise may result in an oxidative stress [5],
which could lead to tissue damage caused by alterations in
protein function [6] or free-radical-mediated lipid peroxidation [7,8].
Damage to muscle cells after acute physical exercise is
most severe when the individual is unaccustomed to the
exercise task and generally results in the appearance of
muscle-derived proteins in the plasma; the plasma activities of creatine kinase (CK), pyruvate kinase and lactate
dehydrogenase are generally taken as indicators of the
extent of muscle damage [9]. A free-radical-mediated
mechanism, involving lipid peroxidation and loss of
membrane integrity, has been postulated as the cause of
delayed-onset muscle soreness after exercise [lo].
An elaborate antioxidant system has evolved to protect
living organisms from oxidative damage [ 113. However,
under conditions of chronic oxidative stress, such as
prolonged exhaustive exercise [7], or in certain nutritional
deficiencies [12, 131 the protective capacity of the antioxidant defence system may be exceeded.
612
J. D. Robertson et al.
While acute exercise may induce oxidative damage
(and muscle soreness) in untrained individuals, there is
evidence that the antioxidant system can adapt to chronic
oxidative stress [ll],such as physical training [14]. In
addition, the magnitude of the increase in the serum
activity of muscle-specific enzymes after exercise depends
on physical conditioning [ 15-1 71.
In this study, we have investigated the relationship
between regular physical training and antioxidant defence
mechanisms in male subjects.
METHODS
Subjects
Twenty-six male volunteers, aged 20-40 years, who
were in approximately steady state with respect to body
weight and physical activity patterns were recruited. Six of
the subjects were classified as sedentary; although not
completely inactive, none was engaged in regular exercise
or had a physically demanding occupation. Subjects who
were overweight were excluded from the study. The entry
criteria for the active group were regular running habits
and energy balance; only subjects who had been running
an approximately constant weekly distance for at least 10
weeks were accepted, and all subjects had been running
regularly for at least 2 years. All subjects were nonsmokers, had no history of medical disorders and were
not taking vitamin supplements.
Subjects recorded their food intake for 7 consecutive
days using scales accurate to 2 g. During this period, they
visited the laboratory between 07.00 and 09.00 hours
after an overnight fast. They sat at rest for 10 min before
blood pressure was measured by auscultation and a
venous blood sample was taken from an antecubital vein
with minimal stasis by using a syringe and needle. The
height and nude body weight of the subjects were then
measured and body fat content was estimated by the skinfold thickness method [18].Data on diet, general health,
normal exercise habits and exercise taken the day before
blood sampling were obtained by using a questionnaire.
Maximum oxygen uptake (Vo,max.) was measured
during an incremental treadmill test, which involved
subjects running on the level at a fixed speed of 10 or 12
km/h for 2 min. The gradient was then increased by 2%
every 2 min until the subject could no longer continue.
Expired air volume, oxygen consumption and carbon
dioxide output were measured by a Gould 9000 IV
automated gas analysis system (Gould Electronics Ltd,
Coventry, U.K.).
Approval for the study was obtained from the Joint
Ethical Committee of the Grampian Health Board and
the University of Aberdeen.
anticoagulant, and (3) 10 ml into a plain glass tube. The
first portion was used for general haematological analysis,
including haemoglobin concentration, measured by the
cyanomethaemoglobin method, and packed cell volume,
determined by using a microhaematocrit centrifuge
(Hawkesley, Lancing, West Sussex, U.K.). The second
portion was centrifuged (3000 g, 10 min) immediately
after collection; the plasma was separated into portions,
one of which (400 111) was mixed with an equal volume of
ice-cold 0.3 mol/l perchloric acid for ascorbic acid
analysis. All samples were stored at -70°C until
analysed. Blood cells were resuspended to the original
volume (20 ml) with phosphate-buffered saline, pH 7.4; 7
ml of this suspension was used in a lymphocyte separation
procedure, and the remainder was stored at - 70°C until
enzyme analysis. Lymphocytes were separated on a
Ficoll-Hypaque gradient (Histopaque-1077; Sigma,
Poole, Dorset, U.K.) by methods described elsewhere
1191. Serum was collected after centrifugation and the
sample was stored at - 70°C until analysis.
Dietary analysis
The composition of foods was estimated from an
expanded version of the tables of McCance & Widdowson [20]. Calculated values of micronutrient intakes have
not been reported, since the food tables may not be
sufficiently reliable for these components.
Vitamin analysis
Plasma and erythrocyte a-tocopherol concentrations
were measured by h.p.1.c. after organic extraction [21].
Ascorbic acid and uric acid concentrations in perchloric
acid-treated plasma or lymphocyte extracts were
measured by h.p.1.c. [ 191.
Plasma analysis
Lipid peroxide concentration was determined as thiobarbituric acid-reactive substances (TBARS) by a
modified fluorometric malondialdehyde assay [22].
Measurement of conjugated dienes was by a first-derivative scan on an organic extract [23]. Cholesterol was
assayed enzymically with the BCL Cholesterol C-System
diagnostic kit (BCL, Lewes, East Sussex, U.K.).
CK ( E C 2.7.3.2) activity at 37°C was determined by an
enzymic method using a commercial kit (Roche Diagnostics, Welwyn Garden City, Herts, U.K.). Caeruloplasmin
( E C 1.16.3.1) activity was assayed using p-phenylenediamine dihydrochloride as substrate [24].
Serum total protein and albumin concentrations were
determined on an SMAC autoanalyser (Technicon,
Chertsey, Surrey, U.K.).
Blood processing
The venous blood samples were dispensed into
portions: (1)2.5 ml of whole blood into a vial containing
EDTA (potassium salt 1 mg/ml) as an anticoagulant, (2)
20 ml into vials containing lithium heparin as an
Erythrocyte indices
Total erythrocyte glutathione (reported as GSH equivalents) content was measured by a modified glutathione
reductase recycling procedure [25]. Oxidized glutathione
613
Blood antioxidants and exercise
(GSSG)was quantified by measuring the total glutathione
present after the derivatization of reduced glutathione
(GSH) with 2-vinylpyridine [26]. GSH content was calculated by difference.
The activities of the following enzymes were measured
by standard methods: glutathione peroxidase (GSHPx;
EC 1.11.1.9) [27], superoxide dismutase (SOD; EC
1.15.1.1) [28] and catalase (CAT EC 1.11.1.6) [29].
Whole-blood selenium content was measured after acid
extraction by fluorescence of a selenium-diaminonaphthalene complex [30]. Erythrocyte creatine content was
measured by the diacetyl-1-naphthol reaction [311, and
reticulocytes were counted on a film pre-stained with
New Methylene Blue [32] and were expressed in absolute
numbers using the erythrocyte count obtained using an
electronic cell counter (Coulter S Plus W, Coulter
Electronic, Luton, Beds, U.K.).
Statistical analysis
Data were analysed using methods for non-parametric
data [33]. The Kendall's coefficients of rank correlation
( rk)were calculated between the blood indices and (1)the
weekly training distance undertaken (taken as zero for the
sedentary subjects),and (2)physical fitness, as assessed by
Vo,max. using data from all 26 subjects. Eighteen subjects
fitted into one of three groups: sedentary ( n = 6 ) , and
those undertaking low (16-43 km/week, n = 6) or high
(80-147 km/week, n = 6 ) weekly training distances [all
the remaining individuals ( n = 8) ran intermediate weekly
training distances]. A Mann-Whitney U-test was used for
the comparison of the running groups with the sedentary
group. Data are expressed as medians with the range in
parentheses.
RESULTS
Anthropometric characteristics
The physical characteristics of the subjects are given in
Table 1. The individuals in the low- and high-training
groups had higher values of Vo'max. than the subjects in
the sedentary group (P<0.05 and P< 0.01, respectively).
Body weight was sigmficantly lower ( P < 0.05) in the hightraining group than in the sedentary group. The percentage body fat values were lower in high-training group
than in both the sedentary group ( P < O . O l ) and the lowtraining group ( P <0.05).
Nutrition
The daily energy intake (Table 1) significantly correlated with the weekly training distance (rk=0.415,
P<O.OOl). The absolute amounts of fat and carbohydrate, but not of protein, consumed increased with the
weekly training distance ( W O . 0 5 and P < O . O l , respectively). The proportion (as the percentage of total energy)
of protein in the diet significantly decreased with the
weekly training distance ( P <0.01). The proportions of
energy intake as carbohydrate were 39.7 (38.5-62.5)% in
the sedentary group, 51.5 (40.4-55.7)% in the lowtraining group and 50.4 (44.4-56.4)% in the high-training
group; a more detailed analysis is given elsewhere [34].
Muscle damage and free-radical involvement
Both groups of runners had higher plasma CK activities than the sedentary group (Table 2). However, aLl three
groups had similar plasma concentrations of TBARS,
although there was a significant negative correlation
Table 1. Physical characteristics, training and daily energy intake for three groups of subjects:
sedentary subjects (n= 6), low-training runners (16-43 km/week, n = 6) and high-training
runners (80-147 kmlweek, n = 6)
A Mann-Whitney U-test was used for comparison of (1)the running groups with the sedentary
group: *P<0.05, **P<O.Ol, (2) the high-training group with the low-training group: aP<0.05,
bP< 0.01. The data are expressed as medians with the range in parentheses.
Age (years)
Height (cm)
Weight (kg)
Body fat (%)
Vo, max.(mi m h - ' kg-I)
Training (km/week)
Energy intake (MJ/day)
Sedentary
subjects
Lowtraining
runners
Hightraining
runners
30
(21-39)
181
(165- 182)
73.5
(60.0-81.2)
17
(12-19)
53.1
(47.2-6 1.0)
0
36
(32-37)
179
(163-194)
71.5
(61.0-90.0)
14
(9-20)
59.9*
(54.2-66.1)
22
(16-43)
13.5
(10.6-14.0)
32
(25-39)
172
(167-179)
58.4*b
(55.3-68.8)
12.4
(9.3-14.7)
(7-11)
74.4**b
(69.0-8 1.7)
123
(80- 147)
13.8
(11.9-17.1)
614
J. D. Robertson et al.
Table 2. Concentrations of antioxidant in blood from the three groups of subjects: sedentary
subjects (n= 6), low-training runners (16-43 km/week, n = 6) and high-training runners
(80-147 km/week, n = 6)
A Mann-Whitney U-test was used for comparison of ( 1 ) the running groups with the sedentary
group: *P< 0.05, **P<O.O1, (2) the high-training group with the low-training group: aP<O.O1.
The data are expressed as medians with the range in parentheses.
training
Hightraining
runners
runners
111
(67- 162)
1.39
(1.06-1.63)
119
(94- 124)
25.7
(5.4-40.9)
206*
(105-338)
1.36
(1.02-1.45)
86
(68-1 82)
13.6
(7.1-36.0)
240**
(110- 1 164)
1.20
(1.00-1.35)
105
(92- 138)
21.0
(10.9-39.6)
7.8
(6.1-8.7)
1.7
( 14.-1.8)
292
(243-339)
35
(27-44)
70
(65-74)
47
(42-48)
7.5
(3.5-8.9)
1.7
(1.4-1.9)
28 1
(274-288)
37
(28-41)
69
(67-70)
46
(44-47)
8.5
(6.4-1 1.9)
1.6
(1.2-2.1)
247*"
(197-263)
36
(31-44)
69
(68-70)
46
(45-47)
Sedentary
subjects
Plasma CK activity (units/l)
Plasma TBARS concn. (pmol/l)
Plasma conjugated diene concn. (arbitraryunits/])
Plasma ascorbic acid concn. (pmol/l)
Low-
Plasma a-tocopherol content
mg/l
g/mol of cholesterol
Plasma uric acid concn. (pmol/l)
Plasma caeruloplasmin activity (units/l)
Serum protein concn. (g/l)
Serum albumin concn. (g/l)
between plasma TBARS concentration and Vo,max.
( r k = -0.340,
P<o.o5). There was no significant difference in the plasma concentration of conjugated dienes
in the three groups or any relationship of this with the
weekly training distance (rk= 0.048) or Vo,max. ( r k =
- 0.009).
Ascorbic acid and vitamin E status
The plasma ascorbic acid concentration was not
related to the weekly training distance, but the lymphocyte ascorbic acid concentration was higher in the hightraining group than the low-training group ( P <0.05).
Erythrocyte a-tocopherol content was significantly
higher in both groups of runners (P<O.O5) than in the
sedentary subjects (Table 3), but there was no correlation
between erythrocyte a-tocopherol content and the
weekly training distance ( r , =0.168, Table 3) or Vo,max.
( r k = 0.058).
Plasma antioxidants
Plasma caeruloplasmin activities and serum protein
and albumin concentrations were similar in the runners
and the sedentary control subjects (Table 2). Plasma uric
acid concentrations showed significant negative correlation with the weekly training distance ( r k = - 0.360,
P<O.O1) and Vo,max. ( r k = -0.290, P<0.05) and was
lower in the high-training group than in the sedentary
group ( P <0.05).
Erythrocyte indices
Mean weekly training was significantly correlated with
the erythrocyte GSHPx ( rk= 0.302, P< 0.05) and CAT
(rk= 0.309, P< 0.05) activities but not with erythrocyte
SOD activity ( r , = - 0.040). Erythrocyte selenium
content (which was correlated with GSHPx, r k = 0.464,
P< 0.00 1) was significantly higher in the high-training
group than in the sedentary group (P<O.O5), and was
correlated with the weekly training distance ( r , = 0.382,
P< 0.01) and Vo,max. ( r , = 0.340, P < 0.01).
Total erythrocyte glutathione content (GSH + 2GSSG)
was significantly, but weakly, correlated with the weekly
training distance ( r , = 0.270, P< 0.05) and was higher in
the two exercise groups than in the sedentary subjects
(Table 3); the increase could be accounted for by an
elevation in the GSH content. Erythrocyte a-tocopherol
content was significantly correlated with total erythrocyte
glutathione content ( r k = 0.525, P< 0.01).
Circulating haemoglobin concentration, reticulocyte
numbers (counts/l) and erythrocyte creatine concentrations showed no significant relationships with the weekly
training distance or Vo,max. In addition, reticulocyte
numbers and erythrocyte creatine concentrations were
not related to the erythrocyte activities of GSHPx or
SOD. Erythrocyte CAT activity was inversely related to
Blood antioxidants and exercise
615
Table 3. Concentrationsof intermediates and activities of antioxidant enzymes in blood cells from
the three groups of subjects: sedentary subjects ( n = 6), low-training runners (16-43 km/week,
n = 6) and high-training runners (80-147 km /week, n = 6)
A Mann-Whitney U-test was used for comparison of (1)the groups of runners with the sedentary
group: *P<O.O5, **P<O.Ol; (2) the high-training group with the low-training group: aP<O.O1.
The data are expressed as medians with the range in parentheses.
Sedentary
subjects
Lowtraining
runners
Hightraining
runners
0.86
(0.38-1.1 8)
0.57
(0.16-0.84)
0.14
(0.10-0.1 8)
1.24*
(0.97-1.68)
0.92**
(0.71-1.22)
0.15
(0.09-0.23)
1.20*
(0.91-1.49)
0.82*
(0.55-0.99)
0.21*
(0.16-0.26)
77.1
(60.7-1 10.8)
817
(346-2017)
1.63
( 1.15-2.21)
0.27
(0.22-0.42)
4.4
(1.2-15.2)
24.6
(16.7-66.3)
93.9
(64.9-100.9)
1009
(894-1574)
1.47
(0.96-1.89)
0.37
(0.26-0.67)
15.2*
(12.8-29.8)
24.3
(16.3-28.3)
98.5*
(80.3-126.5)
1122
(581-2971)
1.65
(1.08-2.53)
0.45*
(0.35-0.69)
14.3*
(9.7-27.0)
38.2"
(13.2-79.5)
Erythrocyte glutathione content (mg/g of Hb)
Total
GSH
GSSG
Erythrocyte GSHPx activity (units/g of Hb)
Erythrocyte CAT activity (arbitrary units/g of Hb)
SOD activity (units/g of Hb)
Erythrocyte Se content (pg/g of Hb)
Erythrocyte vitamin E content (pg/g of Hb)
Lymphocyte ascorbic acid concn. (pmol/g of protein)
reticulocyte count ( r k = -0.40, P<O.O5) and to erythrocyte creatine concentration ( r ,= - 0.380, P < 0.05).
DISCUSSION
The antioxidant defence systems in humans involve a
series of inter-relating components [ 5 , 35, 361, and it is
evident that a number of these are different in runners
compared with sedentary subjects.
When plasma is exposed to oxidative stress in vitro, the
thiol groups, especially those of albumin, caeruloplasmin
and uric acid, are preferentially oxidized [37]. The concentrations of albumin and caeruloplasmin were not
related to the extent of physical training but that of uric
acid was reduced with training, which may be a consequence of an alteration in the metabolism of purines [38].
Ascorbic acid and the tocopherols provide complementary antioxidant protection, in that the former is
present in the aqueous phase and the latter are lipidsoluble. This study indicates that the erythrocyte atocopherol content is increased in trained individuals,
although this appears to be independent of the extent of
training load. The vitamin E content of muscle and liver
from endurance-trained rats is lower than that of tissues
from sedentary rats when the animals are fed a vitamin
E-deficient diet, suggesting increased oxidation of vitamin
E during exercise [39] and a possible reduction in antioxidant protection [40]. The over-compensation for this
increase in vitamin E turnover in our athletes may be due
to an increase in dietary intake of this vitamin and/or an
increase in vitamin E recycling. A similar increase in
erythrocyte vitamin E content was observed in the days
after acute exercise [41]. The increase in the total glutathione and GSH contents in erythrocytes may contribute
to the vitamin E recycling [42]. In addition, glutathione
has been implicated in the restoration of the activity of
thiol-dependent enzymes after exercise-induced inactivation [6].
Ascorbic acid status, as assessed by the ascorbic acid
concentration in lymphocytes, appears to be increased by
prolonged physical training, and this is consistent with the
finding that acute exercise increases lymphocyte ascorbic
acid concentration in the days after exercise [19].
Although we found that plasma ascorbic acid concentration was not related to the extent of physical training,
Fishbaine & Butterfield [43] reported that serum ascorbic
acid concentration reflected activity levels. It seems likely
that stress-related changes in secretion of ascorbic acid
from the adrenal gland greatly reduces the usefulness of
the plasma concentration as an indicator of ascorbic acid
status.
The erythrocyte is extremely well protected from
reactive oxygen species by antioxidant enzymic mechanisms. The activity of two of these, GSHPx and CAT, was
increased in proportion to the weekly training distance,
but the activity of SOD was unaltered. The erythrocyte
population tends to be younger in elite runners [44],
which may account for some increase in the mean GSHPx
activity as erythrocyte GSHPx activity is dependent on
the age of the cell. However, we were unable to demonstrate a relationship between erythrocyte creatine content,
a sensitive indicator of cell age 1451, and the extent of
physical training. Physical training in rats causes proportionate increases in muscle mitochondrial and cyto-
616
J. D. Robertson et al.
solic GSHPx activity [ 141, whereas CAT activity increases
in human erythrocytes [46] and in human skeletal muscle
[47] after training. Indeed, the activities of SOD, CAT and
GSHPx in aerobic cells can be related to the metabolic
rate and the production of oxygen radicals 1111
The validity of using the measurement of antioxidants
in blood as the measure of either overall nutritional status
or general antioxidant potential is different for each
antioxidant. Plasma ascorbic acid concentration may be a
suitable indicator 1481, whereas blood tocopherol content
may not be as reliable 149, 501. Blood selenium content
and the activity of erythrocyte GSHPx may be good
indicators of selenium nutritional status 1511. There is
little information on the sensitivity of other blood antioxidants to changes in their concentrations in other
tissues, except for gross nutritional deficiencies. In addition, there may be tissue-specific changes in antioxidants
due to endurance training. In the rat, endurance training
may result in an increase in muscle activity of CAT but
not of SOD [52], although in a separate study training led
to a reduction in CAT, SOD and vitamin E in cardiac
muscle with GSHPx remaining unchanged 1531.This may
be countered by an increase in the antioxidant potential of
the erythrocyte, which has been shown to cause a
decrease in the reperfusion injury of isolated, ischaemic
rat hearts [54].
One of the consequences of the altered antioxidant
status with physical training could be a reduction in the
muscle soreness and damage that has been found to
follow endurance running [55,561, since a free-radical
mechanism may be involved 110, 571. In this present study
plasma activities of CK were proportional to the extent of
physical training, which suggests a continual degree of
muscle damage. Despite this evidence of muscle damage,
there must still be a significant degree of adaptation to
training, since the plasma CK activity values from
sedentary individuals undertaking the high (running)training load would be expected to be many times higher
~31.
The significant negative correlation between fitness, as
assessed by Vo,max., and plasma TBARS concentration
in this study is consistent with an improvement in the
antioxidant defence mechanism. In rats, exhausting
exercise has been reported to be a factor in decreasing
total thiol groups in hepatic or skeletal muscle mitochondria but these free-radical-mediated protein alterations were not seen after training 161. Similarly, lipid
peroxidation is enhanced in vitro in exhausted control
mice but not in exhausted endurance-trained mice, and
fibre necrosis and inflammation are not observed in
trained mice after exhausting exercise 159, 601. Indeed,
adaptative changes to endurance training in rats have
been shown to abolish the rise in plasma products of lipid
peroxidation seen in untrained animals after acute
exercise 1521, which may account for the lack of change in
plasma TBARS concentration after acute exercise in
trained athletes 141, 611. Thus, endurance training can
induce protection against exercise myopathy.
The observed adaptive changes in the blood antioxidant system may be associated with physical training, but
could also be attributed to an alteration in nutritional
status. The daily energy intake of our subjects was found
to be directly related to the amount of physical training
undertaken [34], and it is therefore possible and indeed
probable that the intake of antioxidants such as vitamin E
and ascorbic acid was also higher. In addition, the
increase in the activity of GSHPx could be a result of an
increased intake of its cofactor, selenium [511, although
nutrient intake, of especially vitamin C, may not show a
simple relationship to energy intake [62].
In conclusion, our results indicate that the protective
antioxidant capacity of blood is enhanced in endurance
runners but, despite these changes, habitual physical
activity may still result in some degree of muscle damage.
Apart from erythrocyte a-tocopherol content, which
increased irrespective of the amount of training, the
improvements in blood antioxidants were related to the
amount of training undertaken. The improvement in the
blood antioxidant potential may be related both to the
physical activity and the dietary intakes of antioxidant
vitamins and trace-element cofactors of antioxidant
enzymes.
ACKNOWLEDGMENTS
We thank Dr P. H. Whiting, Department of Clinical
Biochemistry, University of Aberdeen, for carrying out
determinations of serum total protein and albumin
concentrations, Dr E. R. Skinner, Department of Biochemistry, University of Aberdeen, for performing the
total cholesterol measurements, and A. C. Milne, Rowett
Research Institute, for her help with the dietary analysis.
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