© 2000 American Heart Association, Inc.
Atherosclerosis and Lipoproteins |
Long-Term Effects of Vitamin E, Vitamin C, and Combined Supplementation on Urinary 7-Hydro-8-Oxo-2'-Deoxyguanosine, Serum Cholesterol Oxidation Products, and Oxidation Resistance of Lipids in Nondepleted Men
From the Research Institute of Public Health (E.P.-S., J.T.S., K.N., J.K., R.S., U.R.), University of Kuopio, Kuopio, Finland; Karolinska Institutet (U.D.), Department of Medical Laboratory Sciences and Technology, Division of Clinical Chemistry, Huddinge University Hospital, Huddinge, Sweden; the German Institute of Human Nutrition (R.B.-F.), Potsdam-Rehbrucke; the Department of Clinical Pharmacology (H.E.P.), Rigshospitalet, University Hospital Copenhagen, Copenhagen, Denmark; and the Institute of Public Health (S.L.), Panum Institute, Copenhagen, Denmark.
Correspondence to Prof Jukka T. Salonen, Research Institute of Public Health, University of Kuopio, PO Box 1627, 70211 Kuopio, Finland. E-mail jukka.salonen{at}uku.fi
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Abstract |
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Abstract—We studied the long-term effects of vitamins E and C and their combination on lipid peroxidation in vivo and in vitro. The Antioxidant Supplementation in Atherosclerosis Prevention (ASAP) trial is a double-masked placebo-controlled randomized clinical trial to study the effects of vitamin C (500 mg of slow release ascorbate per day), vitamin E (182 mg of RRR-
-tocopherol acetate per day),
and the combination of both antioxidants. Lipid peroxidation
measurements were carried out for 48 male participants at entry and at
12 and 36 months. Compared with placebo, vitamin E and the vitamin
combination increased plasma lipid–standardized
-tocopherol during the first 12 months by 68.2% and
65.2% (P<0.001 for both), respectively, and reduced
serum 7ß-hydroxycholesterol by 50.4%
(P=0.013) and 44.0% (P=0.041),
respectively. The net change of lipid standardized
-tocopherol was 63.8% after 36 months of vitamin E
supplementation and 43.3% for the combination. Vitamin C
supplementation elevated plasma total ascorbate level by 30.1%
(P=0.043) in 12 months and by 91.1%
(P=0.001) in 36 months. Neither vitamin E, vitamin C,
nor the combination influenced the urinary excretion rate of
7-hydro-8-oxo-2'-deoxyguanosine or the antioxidative capacity of
plasma. Vitamin E and the combination of vitamins E and C enhanced the
oxidation resistance of isolated lipoproteins and total serum lipids.
Our data indicate that long-term supplementation of nondepleted men
with a reasonable dose of vitamin E alone or in combination with slow
release vitamin C reduces lipid peroxidation in vitro and in vivo,
whereas a relatively high dose of vitamin C alone does not.
Key Words: antioxidants • lipid peroxidation • oxidation resistance • 7-hydro-8-oxo-2'-deoxyguanosine • oxysterols
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Introduction |
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Vitamins E1 2 3 4 and C5 6 are widely regarded as important dietary antioxidants. However, this concept is based on in vitro studies and on supplementation trials in which only measurements of lipid peroxidation ex vivo have been performed.3 The evidence of the lipid peroxidation–inhibiting effects of vitamins E and C in vitro is plentiful.1 2 3 4 5 6 7 In addition, oral vitamin E supplementation has consistently increased the oxidation resistance of isolated lipoproteins in vitro.8 9 10 11 12 13 Vitamin C has had been shown to have a similar effect in a few14 15 16 but not in all17 studies. Vitamin C can also act as a pro-oxidant in certain conditions.17 18 In theory, vitamin E could function as a mediator of lipid peroxidation if sufficient coantioxidants are not present.19 20 However, this theory has not been tested in oral supplementation studies with in vivo measurements. There are no previous long-term placebo-controlled oral supplementation trials concerning the effects of these vitamins on lipid peroxidation in nonsmoking clinically healthy subjects.
The assessment of oxidative stress and lipid peroxidation in vivo in humans is problematic. 7-Hydro-8-oxo-2'-deoxyguanosine (8-oxodG), a repair product of oxidative damage to DNA, has been used as an indicator of intracellular oxidative stress.21 22 Some of the preferred measures of lipid peroxidation in vivo are the cholesterol oxidation products.23 24 25 26 27 28 29 In 1994, we started a randomized-factorial, double-masked, placebo-controlled, long-term trial to study the effect of supplementation with vitamins E and C on atherosclerotic progression and the hypothesized pathways of the expected preventive effects. Measurements of in vitro and in vivo lipid peroxidation were carried out at entry and at 12 and 36 months in a subset of 48 male participants. The purpose of the present study was to present results concerning the effects of vitamin E and C supplementation on these measurements.
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Methods |
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Study Design and Supplements
The Antioxidant Supplementation in Atherosclerosis Prevention (ASAP) study was designed to test the main study hypothesis that the supplementation of 45- to 69-year-old smoking and nonsmoking men and postmenopausal women (520 subjects) with either 182 mg of RRR-
-tocopherol or 500
mg of slow-release ascorbic acid daily or both will retard the
progression of common carotid atherosclerosis. ASAP is
a clinical placebo-controlled double-masked trial with 2x2 factorial
design with randomization in 4 balanced strata. Approximately half of
the subjects were regular smokers (
5 cigarettes per day) at
screening. All subjects had
hypercholesterolemia, defined as serum
cholesterol of at least 5.0 mmol/L at screening. The
study consisted of an 8-week placebo lead-in phase and a 3-year
double-masked phase, for which the subjects were randomly allocated to
either (1) 91 mg of RRR--tocopherol (Corresponding to
136 IU of vitamin E and 100 mg of RRR--tocopheryl acetate) twice
daily, (2) 250 mg slow-release ascorbic acid twice daily, (3) both
RRR--tocopherol and ascorbic acid in a single tablet
(CellaVie, Ferrosan A/S), or (4) placebo only. The doses were chosen on
the basis of pilot and kinetic studies.17 22 30 31 The
subjects were randomized separately in 4 strata of approximately equal
size: (1) smoking men, (2) nonsmoking men, (3) smoking postmenopausal
women, and (4) nonsmoking postmenopausal women. All subjects gave a
written informed consent. The study protocol was approved by the
Research Ethics Committee of the University of Kuopio. The subjects came to baseline visits and were randomized between October 1994 and October 1995. The follow-up visits were exactly 12 and 36 months later to avoid the effects of seasonal changes. For the present study, extensive measurements were performed in a subset of 48 consecutive men at the baseline visit between July and October 1995 and at the 12-month and 36-month follow-up visits. Supplements were given, and returned tablets were counted at all these visits. The proportion of tablets used was 92.3%, 94.6%, 94.3%, and 92.3% at 12 months in the vitamin E group, vitamin C group, combination group, and placebo group, respectively. The respective proportions of tablets used at 36 months were 91.9%, 94.4%, 93,8%, and 94.6%.
Subjects were not entered into the trial if they had the following: premenopause or regular oral estrogen substitution therapy (women), regular intake of antioxidants, acetylsalicylic acid, or any other drug with antioxidative properties, severe obesity (body mass index >32 kg/m2), type 1 diabetes, cataracts extracted bilaterally (making opacity assessment impossible), uncontrolled hypertension (sitting diastolic blood pressure >105 mm Hg), any condition-limiting mobility making study visits impossible, severe disease (shortening life expectancy), or other disease or condition worsening the adherence to the measurements or treatment.
Blood Sampling and Urine Collection
Subjects were instructed to abstain from eating for 12 hours and
from ingesting alcohol for a week before blood sampling. After the
subject had rested in a sitting position for 5 minutes, blood was drawn
with Venoject vacuum tubes (Terumo). No tourniquet was used. Blood for
lipoprotein fractionation and plasma total peroxyl radical–trapping
antioxidant parameter (plasma TRAP) was collected in tubes
containing EDTA and handled and measured immediately. Serum lipid
oxidation measurement was performed immediately, and
cholesterol, LDL cholesterol, HDL
cholesterol, and triacylglycerol
measurements were performed in batches every other day. Butylated
hydroxytoluene serum samples for measurements of
cholesterol oxidation products were immediately frozen
to -70°C. Blood for -tocopherol and ascorbic acid
measurements was collected in tubes containing lithium and heparin, and
plasma was stabilized with metaphosphoric acid for ascorbic acid
determination and stored at -70° until used. A 24-hour urine sample
was collected during the 24 hours preceding the visit to the laboratory
for drawing blood.
Measurement of 8-OxodG
Urinary excretion of 8-oxodG was measured by 3D
high-performance liquid chromatography (HPLC)
and electrochemical detection in deep-frozen samples as previously
described in detail for 24-hour urine samples.22 The
baseline and the 12-month samples for each person were measured in
duplicate from the same batch.
Measurement of Cholesterol Oxidation Products
Measurements were performed in deep-frozen baseline and 12-month
butylated hydroxytoluene serum samples. Concentrations of 9
cholesterol oxidation products were determined at the
Karolinska Institute by isotope dilution mass spectrometry and the use
of a deuterated internal standards.23 These were
7-hydroxycholesterol (7OH),
7ß-hydroxycholesterol (7ßOH),
24-hydroxycholesterol, 25-hydroxycholesterol,
27-hydroxycholesterol, 7-oxocholesterol (7K),
cholesterol -epoxide (-EPOX), cholesterol
ß-epoxide (ß-EPOX), and cholestan-3ß,5,6ß-triol
(-TRIOL).
Measurement of Oxidation Resistance of Isolated VLDL+LDL
VLDL and LDL were isolated in a combined fraction from fresh
EDTA plasma by ultracentrifugation at baseline and at
12 and 36 months. Immediately after VLDL+LDL fraction separation, the
EDTA and gradient salts were removed by gel permeation columns, and
VLDL+LDL was exposed to copper-induced oxidation as previously
described.32 Time to maximal oxidation rate (lag time) and
maximum reaction velocity (Vmax) were
determined.
Measurement of Serum Lipid Resistance to Oxidation
Lipoprotein resistance to oxidation in fresh serum at baseline
and at 12 and 36 months was measured with a modification of the method
described by Regnström et al.33 Serum was diluted to
a concentration of 0.67% in 0.02 mol/L PBS, pH 7.4. Oxidation was
initiated by the addition of 100 µL of 1 mmol/L
CuCl2 into 2 mL of diluted prewarmed (30°C)
serum. The formation of conjugated dienes was followed by monitoring
the change in the 234-nm absorbance at 30°C on a Beckman Du 640I
spectrophotometer equipped with a 6-position automatic sample
changer.
Measurement of Plasma TRAP
Plasma TRAP was determined with a modification of the method of
Metsä-Ketelä34 as previously
described35 at baseline and at 12 and 36 months.
Measurement of Vitamins C and E and -CEHC
Ascorbic acid and dehydroascorbic acid were determined in
batches by HPLC.36 The sum of ascorbic acid and
dehydroascorbic acid (total ascorbic acid [TAA]) concentration in
plasma was used for statistical analysis. Heparin plasma for
-tocopherol was extracted with ethanol and hexane and
measured by reversed-phase HPLC.32 The 24-hour urinary
excretion of 1,5,7,8-tetramethyl-2(2'-carboxyethyl)-6-hydroxychroman
(-CEHC) was assessed by gas
chromatography.37
Other Measurements
Serum total cholesterol and
triacylglycerol concentrations were determined
enzymatically (Konelab) with an autoanalyzer (Kone Specific,
Konelab). Serum LDL cholesterol was precipitated by using
polyvinyl sulfate (Boehringer-Mannheim) and calculated as the
difference between total and supernatant cholesterol. Serum
HDL cholesterol was measured after precipitation with
magnesium chloride. All the measurements were performed at baseline and
at 12 and 36 months. Dietary intake of foods and nutrients was assessed
at baseline and at the 36-month study visit by using a 4-day food
recording, which was completed in an interview by a
dietitian.
Statistical Methods
Statistical analyses were carried out by using a
statistical program software system (SPSS 9.0.1 for Windows). To
separate the effect of -tocopherol from that of serum
lipids, lipid-standardized -tocopherol was used in the
statistical analysis.38 The net change was
calculated as the mean change in the supplemented group minus the mean
change in the placebo group. Nonparametric Kruskal-Wallis
1-way ANOVA was used to compare the heterogeneity
between the groups at baseline. Differences in changes between groups
at 12 months and at 36 months were tested by the Mann-Whitney
U test. The 95% CIs were calculated on the basis of
t distribution. Differences in selected baseline
characteristics of the study subjects between smokers and nonsmokers
were tested by parametric Student t test or
nonparametric Mann-Whitney U test. Normality of
distributions was confirmed by the Kolmogorov-Smirnov test.
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Results |
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Baseline Distributions
The main baseline characteristics of the study subjects are presented in Table 1
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There were neither statistically significant nor biologically
meaningful differences between the randomized groups. Serum total
cholesterol and LDL cholesterol were higher
than usual among Finnish men because of the criterion of
hypercholesterolemia (serum
cholesterol 5 mmol/L) at entry. The mean fiber
intake (22.2 g/d) did not reach the Nordic Nutrition
Recommendations39 (25 to 35 g/d) but was precisely the
same as reported earlier among adults in Finland.40 The
official saturated fatty acid recommendation (
10 energy %)
was not reached, with the average intake being 16.7 energy %.
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The study subjects consisted of 26 nonsmokers and 22 smokers
distributed between groups, as shown in Table 1
. Smokers had
30.5% (95% CI 10.9% to 42.0%) lower mean plasma TAA levels and
significantly (P=0.039) shorter serum lipid oxidation lag
times. Serum -TRIOL was nearly significantly (P=0.051)
lower in nonsmokers than in smokers. Other in vivo lipid peroxidation
indicators tended to be nonsignificantly elevated in smokers. There was
no difference between smokers and nonsmokers in either
lipid-standardized plasma -tocopherol, plasma
-tocopherol, oxidation resistance of VLDL+LDL,
antioxidative capacity of plasma, or mean intakes of vitamin E, vitamin
C, or fiber.
Effects of Supplementation on Plasma Total Vitamin C and E
Concentrations
The mean plasma TAA and lipid standardized
-tocopherol concentrations declined significantly during
the first 12 study months in groups that did not get proper
supplementation. The mean plasma TAA was reduced by 28% in the placebo
group and by 41% in the vitamin E group (Table 2). The respective decline in the
lipid-standardized plasma -tocopherol was 31% in the
placebo group and 30% in the vitamin C group (Table 2).
However, plasma -tocopherol was increased slightly (by
1%) in the placebo group and reduced by only 0.6% in the vitamin C
group. After 36 months of supplementation, the mean plasma TAA was
reduced by only 5% in the placebo group and 2% in the vitamin E group
(Table 2). Lipid-standardized plasma -tocopherol
declined by 26% in the placebo group and by 27% in the vitamin C
group (Table 2), whereas plasma -tocopherol was
increased by 12% and by 6%, respectively.
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During the first 12 study months, the net changes of lipid standardized
-tocopherol in vitamin E and combination groups were
68.2% and 65.2%, respectively. During 36 months of supplementation,
the net change was 63.8% in the vitamin E group and 43.3% in the
combination group (Table 2). The mean increase of
lipid-standardized -tocopherol was greater in nonsmokers
than in smokers after 12- and 36-month supplementation periods.
The mean plasma TAA concentration increased from 60.3 to 61.8
µmol/L (by 2%, P=0.043) in the vitamin C group and from
68.9 to 77.2 µmol/L (by 12%, P=0.071) in the vitamin
E+C group during first 12 months. The net changes were 30.1% and
39.6%, respectively. The respective net changes after 36 months of
supplementation were 91.1% and 49.9% (Table 2).
After 12 months of supplementation, the mean decrease of plasma TAA was nonsignificantly greater in nonsmokers than in smokers, whereas after 36 months, the mean increase of plasma vitamin C was greater in smokers (from 59.3 to 86.7 µmol/L) than in nonsmokers (from 80.6 to 97.3 µmol/L).
The 24-hour urinary excretion of the major metabolite of
-tocopherol, -CEHC, was 1.9-fold (P=0.001)
among men who received vitamin E (5.87±0.2.41 mg/d) compared with
placebo (2.04±1.00 mg/d) and 2.4-fold (P=0.000) among men
who received vitamin E+C (7.02±4.18 mg/d) compared with placebo. Among
men who received vitamin E at 12 months, -CEHC was significantly
(P=0.03) greater in nonsmokers than in smokers. The
correlation between lipid-standardized plasma
-tocopherol concentration and urinary -CEHC excretion
at 12 months was 0.62 (P<0.001).
Effects on DNA Oxidation Marker
Neither vitamin C, vitamin E, nor combined supplements had any
statistically significant effect on the urinary excretion rate of
8-oxodG (Table 2).
Effects on In Vivo Lipid Peroxidation Markers
Supplementation with vitamin E reduced (net change) serum
concentration of the principal cholesterol oxidation
product, 7ßOH, by 50% (Table 2) and 7OH by 35%.
Compared with placebo, 12 months of vitamin C supplementation
significantly reduced -EPOX (P=0.049) and ß-EPOX
(P=0.034). The significant net change of 7ßOH was 44% in
the vitamin combination group.
Effects of Ex Vivo Lipid Peroxidation Markers
After 12 months of supplementation, the total serum lipid
resistance to oxidation, measured as lag time, was statistically
significantly decreased in the combination group compared with the
placebo group, whereas decreases in the other groups were not
statistically significant. After 36 months of supplementation, vitamin
E and the combination of vitamins E and C resulted in a significant
increase in lag time. In the vitamin E group, lag time was increased by
8.5%, and in the vitamin E+C group, it was increased by 12.5%.
Neither vitamin E nor vitamin C had any effect on
Vmax. However, after a 12-month supplementation
of vitamin E+C, the decrease of Vmax was
statistically significant compared with the placebo value.
Oxidation resistance of VLDL+LDL increased significantly after the 12- and 36-month supplementation periods in the vitamin E and combination groups compared with the placebo group. During first 12 months, the mean lag time increased by 27.7% in the vitamin E group and by 15.6% in the vitamin E+C group. The respective changes of lag time after 36 months were 27.2% and 21.4%. Vitamin C had no effect on lag time after either 12 or 36 months. Vmax decreased significantly (by 26.5%) after 12 months of supplementation of vitamin E and by 22.0% after 36 months. Compared with placebo, vitamin C and combination supplementation had no statistically significant effect on Vmax.
Neither vitamin E, vitamin C, nor combination supplementation had any
significant effect on the antioxidative capacity of plasma (Table 2).
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Discussion |
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The present study is the first randomized placebo-controlled oral supplementation trial showing an in vivo lipid peroxidation–reducing effect of vitamin E and a combination of vitamins E and C in clinically healthy humans.
During the first 12 months, the mean plasma TAA and lipid standardized
-tocopherol concentrations declined significantly:
plasma TAA in placebo and vitamin E groups and lipid-standardized
-tocopherol in placebo and vitamin C groups. Serum
oxidation resistance, defined as lag time, and plasma TRAP changed
accordingly in the first study year, even though the seasonal changes
were avoided by arranging the follow-up visit exactly 12 months later
than the baseline visit. These changes were probably due to changes in
diet, which we did not assess at the 12-month study visit. After 36
months of supplementation, changes in placebo group were not
statistically significant, and plasma concentrations of
-tocopherol and TAA increased significantly in the
groups that got the respective vitamin supplements. The mean dietary
intake of vitamins E and C, saturated fatty acids, and fiber did not
change significantly in 36 months.
Even though there was no significant difference between smokers and
nonsmokers in plasma -tocopherol, at 12 months the
-CEHC excretion was significantly greater in nonsmokers than in
smokers in the vitamin E group. Generally, smokers suffer from
continuous oxidative stress. They may excrete less -CEHC because
their -tocopherol is used in antioxidative defense and
is not degraded for excretion.
Vitamin E but not vitamin C increased the oxidation resistance of isolated atherogenic lipoproteins (VLDL+LDL). This difference is plausible on the basis of the lipoprotein separation process that eliminates vitamin C from the measurement. However, there are only a few oral supplementation studies concerning the effect of supplementation with ascorbic acid on lipid peroxidation, and the results are not congruent.14 15 16 17 Discrepancy in the results might be due to the difference in the lipoprotein separation procedure or further handling of the samples or may be simply due the difference in the methods used to measure lipid peroxidation.
The difference in change in lag time (VLDL+LDL oxidation) between vitamin E and the combination group was not significant after 12 and 36 months. Also, the 3-year supplementation of vitamin E did not result in longer lag times or lower Vmax than 1-year supplementation; therefore, the maximum effect of vitamin E was achieved during the first year.
A surprising finding was that vitamin C did not improve the antioxidative capacity of plasma in either the 12-month or the 36-month follow-up. In a cross-sectional regression analysis of baseline data of the ASAP study, vitamin C and urate were the strongest determinants of plasma TRAP.35 This is in accordance with a previous supplementation study of 5 men41 and could be due to the nondeficient baseline plasma vitamin C levels of the present subjects.
The combined supplementation of vitamin E+C increased the oxidation resistance of total serum lipids more efficiently than supplementation of vitamin E or vitamin C alone in the 36-month follow-up. During the first 12 months, lag time decreased considerably in each group, except in the combined group. After 36 months of supplementation, the lag time increased in each supplemented group, as was expected. There seemed to be a synergistic interaction between vitamins C and E. Combined supplementation also decreased Vmax significantly at the 12-month follow-up, whereas Vmax increased among the other groups.
The lack of effect of both vitamins on the repair product of DNA oxidative damage is consistent with our previous finding from the shorter-term Multiple Anhoxidane Supplementation Intervention Study (MASI) study.22 Supplementation with exogenous antioxidants does not appear to influence the intracellular oxidative stress, as indicated by the urinary excretion of 8-oxodG.
All previously published placebo-controlled human supplementation
trials with vitamin E have been based mainly on in vitro measurements
of oxidation resistance or susceptibility of isolated lipoproteins.
Vitamin E supplements have, without exception, increased the oxidation
resistance of LDL by 5% to 64% dose-dependently.12 13 In
a study of Reilly et al,42 vitamin E supplementation at
either 100 or 800 U/d failed to reduce the levels of an in vivo
measurement of lipid peroxidation. In another uncontrolled study in 16
women and 6 men who were hypercholesterolemic, Davi et
al43 observed a 34% reduction in 12-hour urinary
8-epiprostaglandin F2 excretion
after 2 weeks of supplementation with 100 mg of
d,l--tocopherol acetate and a 36% reduction after 2
weeks of supplementation with 600 mg.
According to a theory, -tocopherol can promote lipid
peroxidation in human LDL unless coantioxidants are present that
eliminate the chain-carrying -tocopheroxyl
radical.19 The only empirical support has come from in
vitro experiments in which -tocopherol depletion of LDL
made it more resistant to oxidation during "low radical flux
conditions" in the absence of other physiological
antioxidants.44 Our present findings are equivocal in
this respect. Although vitamin E alone reduced the main
cholesterol oxidation product equally to the vitamin
combination, the oxidation resistance of total serum lipids was
enhanced more by the vitamin combination than by either vitamin
alone.
Cholesterol oxidation products have been demonstrated
to be markers for cholesterol autoxidation in
vivo.23 24 25 26 27 28 29 Moreover, the major products of
cholesterol autoxidation are the most commonly detected
oxysterols in foods (7K, 7OH, 7ßOH, -EPOX, and
ß-EPOX).29 Various oxysterols have been detected in
extensive amounts in human tissues and fluids, including human plasma,
atherogenic lipoproteins, and atherosclerotic plaque.29
Among the different oxysterols assayed, 7OH,
24-hydroxycholesterol, and
27-hydroxycholesterol are formed enzymatically as
products of cholesterol catabolism, whereas 7K and
7ßOH are not formed enzymatically in mammals. In the present
randomized, double-masked, placebo-controlled, long-term trial, vitamin
E and the combination supplement consistently reduced 7ßOH.
On the basis of a cell culture study, Colles et al45
concluded that 7ß-hydroperoxy-cholesterol, the labile
precursor of 7ßOH, is the compound predominantly responsible for
oxidized LDL–induced cytotoxicity. In our previous follow-up study,
butylated hydroxytoluene serum 7ßOH concentration was a very strong
predictor of atherosclerotic progression.26 Also,
Carpenter et al46 found high concentrations of 7ßOH
in early atherosclerotic lesions. Lizard et al25
and Deckert et al27 observed that 7ßOH inhibited
arterial relaxation and had the greatest ability to induce
apoptosis in endothelial cells of all
cholesterol oxides measured. Recently, Zieden et
al28 reported that elevated plasma 7ßOH concentration is
an indication of an increased in vivo lipid peroxidation. For these
reasons, we regarded 7ßOH as the most important
cholesterol oxidation measure. Vitamin C supplementation
significantly reduced -EPOX and ß-EPOX. However, the result might
be artifactual, because this oxysterol is easily formed during sample
processing and may be of dietary origin. There are no previous vitamin
E supplementation studies in clinically healthy humans concerning its
effects of oxysterols. Mol et al47 supplemented diabetic
persons and smokers with vitamin E (600 mg/d for 4 weeks) and found
that -TRIOL, 7K, and 7ßOH decreased in diabetic subjects and that
-EPOX decreased in smokers but not in the control subjects.
In conclusion, our present data show that in men who have usual
plasma vitamin C and E levels, long-term oral supplementation with a
reasonable dose of the natural isomer of -tocopherol or
with combined -tocopherol and slow release vitamin C
reduces lipid peroxidation in vivo and in vitro. Our findings further
suggest that a relatively high dose of vitamin C alone does not have
this effect.
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Acknowledgments |
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This work was supported by grants from the Academy of Finland and Henkel Fine Chemicals Division (to J.T.S.), from the Swedish Medical Research Council (to U.D.), and from the Yrjö Jahnsson Foundation, Helsinki, and The Finnish Cultural Foundation of Northern Savo (E.P.-S.). Ferrosan A/S, Denmark, provided the vitamin supplements. We thank public health nurses Hannele Kastarinen and Annikki Konttinen for subject management.
Received February 29, 2000; accepted April 5, 2000.
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