(Circulation. 2001;103:651.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Department of Nephrology, Aalborg Hospital (J.H.C.), Aalborg, Denmark; Department of Medicine, Hjørring/Brønderslev Hospital (H.A.S., V.E.H., E.B.S.), Hjørring, Denmark; Department of Cardiology, Aalborg Hospital (L.F., T.V., E.T.), Aalborg, Denmark; and Medi-Lab (J.D.), Copenhagen, Denmark.
Correspondence to Jeppe Hagstrup Christensen, Department of Nephrology, Aalborg Hospital, PO Box 365, 9100 Aalborg, Denmark. E-mail jhc{at}dadlnet.dk
| Abstract |
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Methods and ResultsWe included 291 patients referred for coronary angiography in whom ischemic heart disease was suspected and all of whom completed a food questionnaire regarding fish and wine intake. The n-3 PUFA composition of granulocyte membranes and of adipose tissue was measured. In addition, 24-hour heart rate variability (HRV) was analyzed. Fish intake was positively associated with the level of n-3 PUFAs in adipose tissue. Significant positive correlation coefficients were found between HRV indices and the levels of n-3 PUFAs in granulocytes. Wine intake was also significantly positively related to HRV, but the patients with the highest wine intake also had the highest intake of fish, as documented by a high n-3 PUFA content in adipose tissue. Multiple linear regression analysis revealed that traditional factors such as treatment with ß-blockers, smoking, age, and previous myocardial infarction were independently related to HRV, and furthermore that n-3 PUFAs (but not wine intake) were significantly independently associated with HRV.
ConclusionsThe close positive association between n-3 PUFAs and HRV in patients suspected of having ischemic heart disease may indicate a protective effect of n-3 PUFAs against SCD. This may partly explain the reduction in SCD observed in humans with a modest intake of n-3 PUFA. Wine intake was also positively correlated with HRV, but this correlation was no longer significant after controlling for the cellular level of n-3 PUFA.
Key Words: fatty acids death, sudden arrhythmia nutrition alcohol
| Introduction |
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The reduced incidence of SCD in relation to dietary n-3 PUFAs has been explained by an antiarrhythmic effect of n-3 PUFAs demonstrated in animal and in vitro studies.4 5 6 In addition, findings that heart rate variability (HRV), an independent predictor of mortality7 8 9 and arrhythmic events,10 is increased by n-3 PUFAs in humans11 12 13 14 may support an antiarrhythmic effect of n-3 PUFAs.
Another dietary approach suggesting a protective effect against cardiovascular death is wine drinking.15 The explanation for this effect is largely unknown, but among other factors, antioxidants present in wine may be beneficial.16 However, recent data also suggest that persons who drink wine may simply eat a healthier diet than abstainers and beer drinkers.17
The aim of the present study was to examine dietary habits concerning fish consumption and wine intake in patients referred for coronary angiography because of suspected ischemic heart disease (IHD) and to relate these findings to biomarkers of fish intake and to 24-hour HRV.
| Methods |
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At least 2 weeks before coronary angiography, the patients were examined at our outpatient clinic, where they completed a food questionnaire and where blood samples were taken, an adipose tissue biopsy sample was obtained, and an ambulatory 24-hour Holter recording was performed. The procedures followed in the study were approved by a regional ethics committee, and signed informed consent was obtained from all the patients.
Food Questionnaire
Patients were asked about their fish consumption at
lunch and at dinner. A score was given according to the following:
never eat fish=1; eat fish once a month=2; eat fish 2 to 3 times a
month=3; eat fish once weekly=4; eat fish 2 to 3 times a week=5; and
eat fish at least once daily=6. Thus, the accumulated fish score for
both lunch and dinner could range from 2 to 12.
Patients were also asked about their drinking habits. The questions were similar to those for fish consumption, ie, never drink wine=1, drink wine once a month=2, etc.
Blood Samples
Blood samples were drawn after
10 hours of fasting.
Granulocytes were isolated from whole blood, and lipids were extracted
and fatty acids esterified as described
previously.18 The content of
n-3 PUFAs in granulocytes and in adipose tissue was measured by gas
chromatography with a Chrompack CP-9002 gas chromatograph (Chrompack
International) and expressed as percent of total fatty
acids.
Adipose Tissue Biopsy
A subcutaneous adipose tissue biopsy sample was
obtained in each patient by a previously described
method,19 with the content
of n-3 PUFAs determined after the fatty acids had been esterified and
extracted as described above.
HRV Analyses
A 24-hour Holter recording was obtained in each
patient on a flash card with a 3-channel digital monitor. The
recordings were analyzed with commercially available software from
Diagnostic Monitoring, which also provided the flash cards and
monitors. The following time-domain HRV variables were
analyzed:
50 ms. QRS complexes with abnormal morphology were excluded from the HRV analysis, and the recordings were processed without knowledge of other patient variables. Owing to the use of digital technology, there were no speed errors in the recordings.
Coronary Angiography
Angiography was obtained from the right femoral
approach. Stenoses of
50% lumen reduction were considered
significant. The patients were divided into 4 groups, those with 0-,
1-, 2-, or 3-vessel disease.
Statistical Analysis
Comparisons of differences between 2 groups were
tested by nonpaired t test for
continuous variables (expressed as mean values and SD), whereas
comparisons between more than 2 groups were analyzed by Kruskal-Wallis
test. The
2 test or Fishers exact test
was used for discrete variables and frequencies. Nonparametric
correlation coefficients (univariate) were calculated between HRV
indices and parameters related to fish consumption and wine intake. To
determine independent correlates of HRV, multivariate linear backward
regression analysis was performed. A
P value <0.05 (2-tailed) was
considered statistically
significant.
| Results |
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Fish Consumption and n-3 PUFA
In
Table 2
, patients fish scores are given, as well as the
content of marine n-3 PUFA (total n-3 PUFA, eicosapentaenoic acid, and
docosahexaenoic acid [DHA]) in cell membranes in granulocytes and in
adipose tissue. Increases in fish intake were reflected in increasing
levels of n-3 PUFAs in both granulocyte membranes and adipose tissue
(correlation coefficients ranging from 0.38 to 0.44,
P<0.001).
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HRV and n-3 PUFA
n-3 PUFAs are incorporated into the bilayer of cell
membranes in the body. Significant positive correlations were found
between n-3 PUFArelated parameters and HRV indices, and as shown in
Table 3
, these correlations were most profound between DHA
levels in granulocytes and HRV.
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In
Table 4
, the 291 patients have been characterized according
to the content of DHA in granulocytes. When the patients were divided
into DHA quartiles, the groups were comparable with respect to age,
body mass index, left ventricular ejection fraction, cardiovascular
medications used, number of smokers, number of patients with a
previous MI, and degree of coronary artery disease. There was a trend
toward greater HRV among those with the highest DHA content with
significantly higher RR and SDNNindex
(Table 4
).
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HRV, Wine Intake, and Fish Consumption
The HRV indices SDNN, SDNNindex, and SDANNindex
increased with increasing intake of wine
(r=0.157,
P=0.01;
r=0.184,
P<0.01; and
r=0.132,
P<0.05, respectively), but
patients with a high wine intake also had higher fish consumption,
reflected by a higher concentration of DHA in adipose tissue
(Figure
).
The linear correlation between SDNN, SDNNindex, and SDANNindex and wine
intake became insignificant after controlling for the cellular level of
DHA (data not shown). However, the positive correlation between DHA in
granulocytes and the HRV indices SDNN, SDNNindex, and SDANNindex
remained significant after controlling for wine intake
(r=0.128,
P<0.05;
r=0.155,
P=0.01; and
r=0.120,
P<0.05,
respectively).
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When patients with no wine intake were compared with those with daily wine intake, the 2 groups were comparable with respect to age, body mass index, ventricular ejection fraction, smoking habits, cardiovascular medications used, degree of coronary artery disease, and number of patients with a previous MI (data not shown). With regard to beer intake, no association was found with either HRV or fish intake.
Independent Correlates of HRV
In a multiple linear regression analysis, traditional
modifiable and nonmodifiable parameters were included as independent
factors along with factors related to fish intake. The dependent
parameters in the analysis were HRV indices. From
Table 5
, it is seen that treatment with ß-blockers, fish
score, and the content of n-3 PUFAs in adipose tissue and in
granulocytes were each independently correlated with HRV indices; in
addition, smoking, age, and previous MI independently had an impact on
HRV.
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| Discussion |
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HRV was also positively related to wine intake. This could in and of itself be an explanation for the better survival among wine drinkers compared with abstainers, but a more likely explanation may be that fish and wine intake are associated.17 Thus, patients with the highest wine intake also had the highest consumption of fish, as documented by the high n-3 PUFA content in adipose tissue, and the positive association between SDNN and wine intake was dependent of the cellular level of DHA. Thus, wine intake was not independently correlated with any of the HRV indices.
SCD is often the first manifestation of IHD and is
responsible for
50% of the mortality from IHD in Western
countries.22 The magnitude
of the problem is illustrated by a recent British study reporting that
74% of fatal events among patients with heart disease happened outside
the hospital.23 Because of
their low cost and small number of side effects, n-3 PUFAs may thus
play a role in the secondary prevention of SCD, not only for high-risk
patients but for all patients suspected of having IHD.
In our patients, n-3 PUFAs were derived from fish, as
demonstrated by the close positive association between fish intake and
the level of n-3 PUFA in adipose tissue. Thus, adipose tissue DHA
content is the biomarker of choice for the assessment of long-term
habitual dietary intake of n-3 PUFAs from
fish.24 The cell membrane
phospholipid fatty acid composition of n-3 PUFAs, on the other hand,
probably reflects the effect of dietary n-3 PUFA intake on changes
responsible for the reduction in
SCD25 and is merely a
physiological marker of dietary n-3 PUFAs. This is in accordance with
the significant positive correlations observed particularly between
cellular DHA levels and HRV indices in our study. We previously
reported a beneficial effect of n-3 PUFA on HRV in patients at high
risk for SCD. In an intervention trial comprising 55 post-MI patients
with a ventricular ejection fraction
0.40, 24-hour HRV significantly
increased in the n-3 fatty acid group compared with the placebo
group.11 Also, in these
patients, a positive significant correlation was found between baseline
levels of n-3 PUFAs in cell membranes and
HRV.12 In addition, we found
a positive association between cellular levels of n-3 PUFAs and HRV in
patients with chronic renal
failure13 and in healthy
subjects in whom HRV increased in a dose-dependent way after
dietary supplementation with n-3
PUFA.14
The mechanism by which increased levels of n-3 PUFA affect HRV indices is not fully understood but may be explained in part by the antiarrhythmic properties of n-3 PUFAs observed in animal and in vitro studies.4 5 6 26 Considerable evidence exists that a change in the lipid composition of biological membranes is closely associated with alterations in their function, and in almost all studies with dietary supplementation with n-3 PUFAs, an increase in phospholipid eicosapentaenoic acid and DHA in cell membranes has been observed. Often, these alterations in the fatty acid composition of the cell membrane change the membrane fluidity, which may be crucial because the fluidity of the cell membrane may provide a dynamic basis for enzyme and receptor functions that secondarily leads to changes in Ca2+ fluxes across the cell membranes and may change the affinity of ß-receptor complexes.27 Other mechanisms could also be involved in the antiarrhythmic actions of n-3 PUFAs27 (and actions on HRV), and further research in this area is needed.
Our results are in line with large human trials with hard end points that indicated an antiarrhythmic effect of n-3 PUFAs. In the recently published GISSI-Prevenzione trial, 11 324 patients with a previous MI were randomized to 0.85 g daily of fish oil or control for up to 3.5 years.1 A reduction in cardiovascular mortality by 15% to 20% and a 45% reduction in SCD was observed in the n-3 PUFA group. This trial thus confirmed the results from the landmark Diet And Reinfarction Trial (DART)20 comprising >2000 men with a previous MI, in which men advised to eat fatty fish at least twice a week had a 29% reduction in total mortality after 2 years, which was thought to be due to an antiarrhythmic effect of n-3 PUFAs.
Two studies have related fish intake to the risk of SCD in patients without prior MI. A population-based case-control study2 with 334 cases of primary cardiac arrest and 493 controls concluded that dietary intake of n-3 PUFA equal to 1 fatty fish meal per week was associated with a 50% reduction in the risk of primary cardiac arrest compared with no intake of fish. In the US Physicians Health Study,3 20 551 male physicians were followed for up to 11 years, and consumption of fish at least once a week was associated with a 52% reduction in the risk of SCD compared with men who consumed fish less than monthly. In these 2 studies, increasing the fish intake further to more than once a week seemed not to influence the risk of SCD, although in the case-control study, the risk of SCD decreased linearly with increasing levels of n-3 PUFAs in cell membranes.2 The authors stated that the effect of dietary fatty acids on the risk of SCD was mediated through changes in cell membrane fatty acid composition.
Epidemiological data suggest that drinking wine is associated with decreased cardiovascular mortality.15 In a prospective population study,28 mortality decreased with increasing intake of wine, whereas this was not observed for intake of beer or spirits. However, a recent cross-sectional study including 48 763 men and women found that wine drinking was associated with a healthy diet, including a high fish intake.17 In our patients, we did not find any association of beer intake with either HRV, fish intake, or levels of n-3 PUFAs in adipose tissue. However, our findings of an association between n-3 PUFAs, wine intake, and HRV may have implications for the interpretation of previous reports on the relation between alcoholic beverage intake and cardiovascular mortality, especially reports that do not control for fish intake.
In conclusion, our study demonstrates a significant positive association between n-3 PUFAs and HRV indices in a well-characterized group of patients suspected of having IHD. The results may indicate a protective effect of n-3 PUFAs against SCD that may partly explain the substantial reduction in SCD observed in other trials among humans with a modest intake of n-3 PUFAs. Finally, the study adds to our knowledge of the potential beneficial effect of wine consumption on cardiovascular events by highlighting the increased fish intake among wine drinkers as a mutually beneficial factor. Further studies are needed, although an intervention trial with alcohol is not realistic.
| Acknowledgments |
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Received June 12, 2000; revision received September 27, 2000; accepted September 27, 2000.
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